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rust / rust-lang / rust / refs/heads/lcnr/rustc-dev-guide / . / compiler / rustc_lint_defs / src / builtin.rs
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//! Some lints that are built in to the compiler.
//!
//! These are the built-in lints that are emitted direct in the main
//! compiler code, rather than using their own custom pass. Those
//! lints are all available in `rustc_lint::builtin`.
//!
//! When removing a lint, make sure to also add a call to `register_removed` in
//! compiler/rustc_lint/src/lib.rs.
use rustc_span::edition::Edition;
use crate::{FutureIncompatibilityReason, declare_lint, declare_lint_pass};
declare_lint_pass! {
/// Does nothing as a lint pass, but registers some `Lint`s
/// that are used by other parts of the compiler.
HardwiredLints => [
// tidy-alphabetical-start
AARCH64_SOFTFLOAT_NEON,
ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
AMBIGUOUS_ASSOCIATED_ITEMS,
AMBIGUOUS_GLOB_IMPORTS,
AMBIGUOUS_GLOB_REEXPORTS,
ARITHMETIC_OVERFLOW,
ASM_SUB_REGISTER,
BAD_ASM_STYLE,
BARE_TRAIT_OBJECTS,
BINDINGS_WITH_VARIANT_NAME,
BREAK_WITH_LABEL_AND_LOOP,
COHERENCE_LEAK_CHECK,
CONFLICTING_REPR_HINTS,
CONST_EVALUATABLE_UNCHECKED,
CONST_ITEM_MUTATION,
DEAD_CODE,
DEPENDENCY_ON_UNIT_NEVER_TYPE_FALLBACK,
DEPRECATED,
DEPRECATED_IN_FUTURE,
DEPRECATED_SAFE_2024,
DEPRECATED_WHERE_CLAUSE_LOCATION,
DUPLICATE_MACRO_ATTRIBUTES,
ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
ELIDED_LIFETIMES_IN_PATHS,
EXPLICIT_BUILTIN_CFGS_IN_FLAGS,
EXPORTED_PRIVATE_DEPENDENCIES,
FFI_UNWIND_CALLS,
FORBIDDEN_LINT_GROUPS,
FUNCTION_ITEM_REFERENCES,
FUZZY_PROVENANCE_CASTS,
HIDDEN_GLOB_REEXPORTS,
ILL_FORMED_ATTRIBUTE_INPUT,
INCOMPLETE_INCLUDE,
INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
INLINE_NO_SANITIZE,
INVALID_DOC_ATTRIBUTES,
INVALID_MACRO_EXPORT_ARGUMENTS,
INVALID_TYPE_PARAM_DEFAULT,
IRREFUTABLE_LET_PATTERNS,
LARGE_ASSIGNMENTS,
LATE_BOUND_LIFETIME_ARGUMENTS,
LEGACY_DERIVE_HELPERS,
LINKER_MESSAGES,
LONG_RUNNING_CONST_EVAL,
LOSSY_PROVENANCE_CASTS,
MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
MACRO_USE_EXTERN_CRATE,
MALFORMED_DIAGNOSTIC_ATTRIBUTES,
MALFORMED_DIAGNOSTIC_FORMAT_LITERALS,
META_VARIABLE_MISUSE,
MISPLACED_DIAGNOSTIC_ATTRIBUTES,
MISSING_ABI,
MISSING_UNSAFE_ON_EXTERN,
MUST_NOT_SUSPEND,
NAMED_ARGUMENTS_USED_POSITIONALLY,
NEVER_TYPE_FALLBACK_FLOWING_INTO_UNSAFE,
NON_CONTIGUOUS_RANGE_ENDPOINTS,
NON_EXHAUSTIVE_OMITTED_PATTERNS,
OUT_OF_SCOPE_MACRO_CALLS,
OVERLAPPING_RANGE_ENDPOINTS,
PATTERNS_IN_FNS_WITHOUT_BODY,
PRIVATE_BOUNDS,
PRIVATE_INTERFACES,
PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
PUB_USE_OF_PRIVATE_EXTERN_CRATE,
REDUNDANT_IMPORTS,
REDUNDANT_LIFETIMES,
REFINING_IMPL_TRAIT_INTERNAL,
REFINING_IMPL_TRAIT_REACHABLE,
RENAMED_AND_REMOVED_LINTS,
REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS,
RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
RUST_2021_INCOMPATIBLE_OR_PATTERNS,
RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
RUST_2021_PRELUDE_COLLISIONS,
RUST_2024_GUARDED_STRING_INCOMPATIBLE_SYNTAX,
RUST_2024_INCOMPATIBLE_PAT,
RUST_2024_PRELUDE_COLLISIONS,
SELF_CONSTRUCTOR_FROM_OUTER_ITEM,
SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
SINGLE_USE_LIFETIMES,
SOFT_UNSTABLE,
STABLE_FEATURES,
SUPERTRAIT_ITEM_SHADOWING_DEFINITION,
SUPERTRAIT_ITEM_SHADOWING_USAGE,
TAIL_EXPR_DROP_ORDER,
TEST_UNSTABLE_LINT,
TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
TEXT_DIRECTION_CODEPOINT_IN_LITERAL,
TRIVIAL_CASTS,
TRIVIAL_NUMERIC_CASTS,
TYVAR_BEHIND_RAW_POINTER,
UNCONDITIONAL_PANIC,
UNCONDITIONAL_RECURSION,
UNCOVERED_PARAM_IN_PROJECTION,
UNEXPECTED_CFGS,
UNFULFILLED_LINT_EXPECTATIONS,
UNINHABITED_STATIC,
UNKNOWN_CRATE_TYPES,
UNKNOWN_DIAGNOSTIC_ATTRIBUTES,
UNKNOWN_LINTS,
UNNAMEABLE_TEST_ITEMS,
UNNAMEABLE_TYPES,
UNREACHABLE_CODE,
UNREACHABLE_PATTERNS,
UNSAFE_ATTR_OUTSIDE_UNSAFE,
UNSAFE_OP_IN_UNSAFE_FN,
UNSTABLE_NAME_COLLISIONS,
UNSTABLE_SYNTAX_PRE_EXPANSION,
UNSUPPORTED_CALLING_CONVENTIONS,
UNUSED_ASSIGNMENTS,
UNUSED_ASSOCIATED_TYPE_BOUNDS,
UNUSED_ATTRIBUTES,
UNUSED_CRATE_DEPENDENCIES,
UNUSED_EXTERN_CRATES,
UNUSED_FEATURES,
UNUSED_IMPORTS,
UNUSED_LABELS,
UNUSED_LIFETIMES,
UNUSED_MACROS,
UNUSED_MACRO_RULES,
UNUSED_MUT,
UNUSED_QUALIFICATIONS,
UNUSED_UNSAFE,
UNUSED_VARIABLES,
USELESS_DEPRECATED,
WARNINGS,
// tidy-alphabetical-end
]
}
declare_lint! {
/// The `forbidden_lint_groups` lint detects violations of
/// `forbid` applied to a lint group. Due to a bug in the compiler,
/// these used to be overlooked entirely. They now generate a warning.
///
/// ### Example
///
/// ```rust
/// #![forbid(warnings)]
/// #![warn(bad_style)]
///
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Recommended fix
///
/// If your crate is using `#![forbid(warnings)]`,
/// we recommend that you change to `#![deny(warnings)]`.
///
/// ### Explanation
///
/// Due to a compiler bug, applying `forbid` to lint groups
/// previously had no effect. The bug is now fixed but instead of
/// enforcing `forbid` we issue this future-compatibility warning
/// to avoid breaking existing crates.
pub FORBIDDEN_LINT_GROUPS,
Warn,
"applying forbid to lint-groups",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #81670 <https://github.com/rust-lang/rust/issues/81670>",
report_in_deps: true,
};
}
declare_lint! {
/// The `ill_formed_attribute_input` lint detects ill-formed attribute
/// inputs that were previously accepted and used in practice.
///
/// ### Example
///
/// ```rust,compile_fail
/// #[inline = "this is not valid"]
/// fn foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previously, inputs for many built-in attributes weren't validated and
/// nonsensical attribute inputs were accepted. After validation was
/// added, it was determined that some existing projects made use of these
/// invalid forms. This is a [future-incompatible] lint to transition this
/// to a hard error in the future. See [issue #57571] for more details.
///
/// Check the [attribute reference] for details on the valid inputs for
/// attributes.
///
/// [issue #57571]: https://github.com/rust-lang/rust/issues/57571
/// [attribute reference]: https://doc.rust-lang.org/nightly/reference/attributes.html
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub ILL_FORMED_ATTRIBUTE_INPUT,
Deny,
"ill-formed attribute inputs that were previously accepted and used in practice",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #57571 <https://github.com/rust-lang/rust/issues/57571>",
report_in_deps: true,
};
crate_level_only
}
declare_lint! {
/// The `conflicting_repr_hints` lint detects [`repr` attributes] with
/// conflicting hints.
///
/// [`repr` attributes]: https://doc.rust-lang.org/reference/type-layout.html#representations
///
/// ### Example
///
/// ```rust,compile_fail
/// #[repr(u32, u64)]
/// enum Foo {
/// Variant1,
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The compiler incorrectly accepted these conflicting representations in
/// the past. This is a [future-incompatible] lint to transition this to a
/// hard error in the future. See [issue #68585] for more details.
///
/// To correct the issue, remove one of the conflicting hints.
///
/// [issue #68585]: https://github.com/rust-lang/rust/issues/68585
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub CONFLICTING_REPR_HINTS,
Deny,
"conflicts between `#[repr(..)]` hints that were previously accepted and used in practice",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #68585 <https://github.com/rust-lang/rust/issues/68585>",
report_in_deps: true,
};
}
declare_lint! {
/// The `meta_variable_misuse` lint detects possible meta-variable misuse
/// in macro definitions.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(meta_variable_misuse)]
///
/// macro_rules! foo {
/// () => {};
/// ($( $i:ident = $($j:ident),+ );*) => { $( $( $i = $k; )+ )* };
/// }
///
/// fn main() {
/// foo!();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// There are quite a few different ways a [`macro_rules`] macro can be
/// improperly defined. Many of these errors were previously only detected
/// when the macro was expanded or not at all. This lint is an attempt to
/// catch some of these problems when the macro is *defined*.
///
/// This lint is "allow" by default because it may have false positives
/// and other issues. See [issue #61053] for more details.
///
/// [`macro_rules`]: https://doc.rust-lang.org/reference/macros-by-example.html
/// [issue #61053]: https://github.com/rust-lang/rust/issues/61053
pub META_VARIABLE_MISUSE,
Allow,
"possible meta-variable misuse at macro definition"
}
declare_lint! {
/// The `incomplete_include` lint detects the use of the [`include!`]
/// macro with a file that contains more than one expression.
///
/// [`include!`]: https://doc.rust-lang.org/std/macro.include.html
///
/// ### Example
///
/// ```rust,ignore (needs separate file)
/// fn main() {
/// include!("foo.txt");
/// }
/// ```
///
/// where the file `foo.txt` contains:
///
/// ```text
/// println!("hi!");
/// ```
///
/// produces:
///
/// ```text
/// error: include macro expected single expression in source
/// --> foo.txt:1:14
/// |
/// 1 | println!("1");
/// | ^
/// |
/// = note: `#[deny(incomplete_include)]` on by default
/// ```
///
/// ### Explanation
///
/// The [`include!`] macro is currently only intended to be used to
/// include a single [expression] or multiple [items]. Historically it
/// would ignore any contents after the first expression, but that can be
/// confusing. In the example above, the `println!` expression ends just
/// before the semicolon, making the semicolon "extra" information that is
/// ignored. Perhaps even more surprising, if the included file had
/// multiple print statements, the subsequent ones would be ignored!
///
/// One workaround is to place the contents in braces to create a [block
/// expression]. Also consider alternatives, like using functions to
/// encapsulate the expressions, or use [proc-macros].
///
/// This is a lint instead of a hard error because existing projects were
/// found to hit this error. To be cautious, it is a lint for now. The
/// future semantics of the `include!` macro are also uncertain, see
/// [issue #35560].
///
/// [items]: https://doc.rust-lang.org/reference/items.html
/// [expression]: https://doc.rust-lang.org/reference/expressions.html
/// [block expression]: https://doc.rust-lang.org/reference/expressions/block-expr.html
/// [proc-macros]: https://doc.rust-lang.org/reference/procedural-macros.html
/// [issue #35560]: https://github.com/rust-lang/rust/issues/35560
pub INCOMPLETE_INCLUDE,
Deny,
"trailing content in included file"
}
declare_lint! {
/// The `arithmetic_overflow` lint detects that an arithmetic operation
/// will [overflow].
///
/// [overflow]: https://doc.rust-lang.org/reference/expressions/operator-expr.html#overflow
///
/// ### Example
///
/// ```rust,compile_fail
/// 1_i32 << 32;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is very likely a mistake to perform an arithmetic operation that
/// overflows its value. If the compiler is able to detect these kinds of
/// overflows at compile-time, it will trigger this lint. Consider
/// adjusting the expression to avoid overflow, or use a data type that
/// will not overflow.
pub ARITHMETIC_OVERFLOW,
Deny,
"arithmetic operation overflows",
@eval_always = true
}
declare_lint! {
/// The `unconditional_panic` lint detects an operation that will cause a
/// panic at runtime.
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![allow(unused)]
/// let x = 1 / 0;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This lint detects code that is very likely incorrect because it will
/// always panic, such as division by zero and out-of-bounds array
/// accesses. Consider adjusting your code if this is a bug, or using the
/// `panic!` or `unreachable!` macro instead in case the panic is intended.
pub UNCONDITIONAL_PANIC,
Deny,
"operation will cause a panic at runtime",
@eval_always = true
}
declare_lint! {
/// The `unused_imports` lint detects imports that are never used.
///
/// ### Example
///
/// ```rust
/// use std::collections::HashMap;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused imports may signal a mistake or unfinished code, and clutter
/// the code, and should be removed. If you intended to re-export the item
/// to make it available outside of the module, add a visibility modifier
/// like `pub`.
pub UNUSED_IMPORTS,
Warn,
"imports that are never used"
}
declare_lint! {
/// The `redundant_imports` lint detects imports that are redundant due to being
/// imported already; either through a previous import, or being present in
/// the prelude.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(redundant_imports)]
/// use std::option::Option::None;
/// fn foo() -> Option<i32> { None }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Redundant imports are unnecessary and can be removed to simplify code.
/// If you intended to re-export the item to make it available outside of the
/// module, add a visibility modifier like `pub`.
pub REDUNDANT_IMPORTS,
Allow,
"imports that are redundant due to being imported already"
}
declare_lint! {
/// The `must_not_suspend` lint guards against values that shouldn't be held across suspend points
/// (`.await`)
///
/// ### Example
///
/// ```rust
/// #![feature(must_not_suspend)]
/// #![warn(must_not_suspend)]
///
/// #[must_not_suspend]
/// struct SyncThing {}
///
/// async fn yield_now() {}
///
/// pub async fn uhoh() {
/// let guard = SyncThing {};
/// yield_now().await;
/// let _guard = guard;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The `must_not_suspend` lint detects values that are marked with the `#[must_not_suspend]`
/// attribute being held across suspend points. A "suspend" point is usually a `.await` in an async
/// function.
///
/// This attribute can be used to mark values that are semantically incorrect across suspends
/// (like certain types of timers), values that have async alternatives, and values that
/// regularly cause problems with the `Send`-ness of async fn's returned futures (like
/// `MutexGuard`'s)
///
pub MUST_NOT_SUSPEND,
Allow,
"use of a `#[must_not_suspend]` value across a yield point",
@feature_gate = must_not_suspend;
}
declare_lint! {
/// The `unused_extern_crates` lint guards against `extern crate` items
/// that are never used.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(unused_extern_crates)]
/// #![deny(warnings)]
/// extern crate proc_macro;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// `extern crate` items that are unused have no effect and should be
/// removed. Note that there are some cases where specifying an `extern
/// crate` is desired for the side effect of ensuring the given crate is
/// linked, even though it is not otherwise directly referenced. The lint
/// can be silenced by aliasing the crate to an underscore, such as
/// `extern crate foo as _`. Also note that it is no longer idiomatic to
/// use `extern crate` in the [2018 edition], as extern crates are now
/// automatically added in scope.
///
/// This lint is "allow" by default because it can be noisy, and produce
/// false-positives. If a dependency is being removed from a project, it
/// is recommended to remove it from the build configuration (such as
/// `Cargo.toml`) to ensure stale build entries aren't left behind.
///
/// [2018 edition]: https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-clarity.html#no-more-extern-crate
pub UNUSED_EXTERN_CRATES,
Allow,
"extern crates that are never used"
}
declare_lint! {
/// The `unused_crate_dependencies` lint detects crate dependencies that
/// are never used.
///
/// ### Example
///
/// ```rust,ignore (needs extern crate)
/// #![deny(unused_crate_dependencies)]
/// ```
///
/// This will produce:
///
/// ```text
/// error: extern crate `regex` is unused in crate `lint_example`
/// |
/// = help: remove the dependency or add `use regex as _;` to the crate root
/// note: the lint level is defined here
/// --> src/lib.rs:1:9
/// |
/// 1 | #![deny(unused_crate_dependencies)]
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^
/// ```
///
/// ### Explanation
///
/// After removing the code that uses a dependency, this usually also
/// requires removing the dependency from the build configuration.
/// However, sometimes that step can be missed, which leads to time wasted
/// building dependencies that are no longer used. This lint can be
/// enabled to detect dependencies that are never used (more specifically,
/// any dependency passed with the `--extern` command-line flag that is
/// never referenced via [`use`], [`extern crate`], or in any [path]).
///
/// This lint is "allow" by default because it can provide false positives
/// depending on how the build system is configured. For example, when
/// using Cargo, a "package" consists of multiple crates (such as a
/// library and a binary), but the dependencies are defined for the
/// package as a whole. If there is a dependency that is only used in the
/// binary, but not the library, then the lint will be incorrectly issued
/// in the library.
///
/// [path]: https://doc.rust-lang.org/reference/paths.html
/// [`use`]: https://doc.rust-lang.org/reference/items/use-declarations.html
/// [`extern crate`]: https://doc.rust-lang.org/reference/items/extern-crates.html
pub UNUSED_CRATE_DEPENDENCIES,
Allow,
"crate dependencies that are never used",
crate_level_only
}
declare_lint! {
/// The `unused_qualifications` lint detects unnecessarily qualified
/// names.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(unused_qualifications)]
/// mod foo {
/// pub fn bar() {}
/// }
///
/// fn main() {
/// use foo::bar;
/// foo::bar();
/// bar();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// If an item from another module is already brought into scope, then
/// there is no need to qualify it in this case. You can call `bar()`
/// directly, without the `foo::`.
///
/// This lint is "allow" by default because it is somewhat pedantic, and
/// doesn't indicate an actual problem, but rather a stylistic choice, and
/// can be noisy when refactoring or moving around code.
pub UNUSED_QUALIFICATIONS,
Allow,
"detects unnecessarily qualified names"
}
declare_lint! {
/// The `unknown_lints` lint detects unrecognized lint attributes.
///
/// ### Example
///
/// ```rust
/// #![allow(not_a_real_lint)]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is usually a mistake to specify a lint that does not exist. Check
/// the spelling, and check the lint listing for the correct name. Also
/// consider if you are using an old version of the compiler, and the lint
/// is only available in a newer version.
pub UNKNOWN_LINTS,
Warn,
"unrecognized lint attribute",
@eval_always = true
}
declare_lint! {
/// The `unfulfilled_lint_expectations` lint detects when a lint expectation is
/// unfulfilled.
///
/// ### Example
///
/// ```rust
/// #[expect(unused_variables)]
/// let x = 10;
/// println!("{}", x);
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The `#[expect]` attribute can be used to create a lint expectation. The
/// expectation is fulfilled, if a `#[warn]` attribute at the same location
/// would result in a lint emission. If the expectation is unfulfilled,
/// because no lint was emitted, this lint will be emitted on the attribute.
///
pub UNFULFILLED_LINT_EXPECTATIONS,
Warn,
"unfulfilled lint expectation"
}
declare_lint! {
/// The `unused_variables` lint detects variables which are not used in
/// any way.
///
/// ### Example
///
/// ```rust
/// let x = 5;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused variables may signal a mistake or unfinished code. To silence
/// the warning for the individual variable, prefix it with an underscore
/// such as `_x`.
pub UNUSED_VARIABLES,
Warn,
"detect variables which are not used in any way"
}
declare_lint! {
/// The `unused_assignments` lint detects assignments that will never be read.
///
/// ### Example
///
/// ```rust
/// let mut x = 5;
/// x = 6;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused assignments may signal a mistake or unfinished code. If the
/// variable is never used after being assigned, then the assignment can
/// be removed. Variables with an underscore prefix such as `_x` will not
/// trigger this lint.
pub UNUSED_ASSIGNMENTS,
Warn,
"detect assignments that will never be read"
}
declare_lint! {
/// The `dead_code` lint detects unused, unexported items.
///
/// ### Example
///
/// ```rust
/// fn foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Dead code may signal a mistake or unfinished code. To silence the
/// warning for individual items, prefix the name with an underscore such
/// as `_foo`. If it was intended to expose the item outside of the crate,
/// consider adding a visibility modifier like `pub`.
///
/// To preserve the numbering of tuple structs with unused fields,
/// change the unused fields to have unit type or use
/// `PhantomData`.
///
/// Otherwise consider removing the unused code.
///
/// ### Limitations
///
/// Removing fields that are only used for side-effects and never
/// read will result in behavioral changes. Examples of this
/// include:
///
/// - If a field's value performs an action when it is dropped.
/// - If a field's type does not implement an auto trait
/// (e.g. `Send`, `Sync`, `Unpin`).
///
/// For side-effects from dropping field values, this lint should
/// be allowed on those fields. For side-effects from containing
/// field types, `PhantomData` should be used.
pub DEAD_CODE,
Warn,
"detect unused, unexported items"
}
declare_lint! {
/// The `unused_attributes` lint detects attributes that were not used by
/// the compiler.
///
/// ### Example
///
/// ```rust
/// #![ignore]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused [attributes] may indicate the attribute is placed in the wrong
/// position. Consider removing it, or placing it in the correct position.
/// Also consider if you intended to use an _inner attribute_ (with a `!`
/// such as `#![allow(unused)]`) which applies to the item the attribute
/// is within, or an _outer attribute_ (without a `!` such as
/// `#[allow(unused)]`) which applies to the item *following* the
/// attribute.
///
/// [attributes]: https://doc.rust-lang.org/reference/attributes.html
pub UNUSED_ATTRIBUTES,
Warn,
"detects attributes that were not used by the compiler"
}
declare_lint! {
/// The `unreachable_code` lint detects unreachable code paths.
///
/// ### Example
///
/// ```rust,no_run
/// panic!("we never go past here!");
///
/// let x = 5;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unreachable code may signal a mistake or unfinished code. If the code
/// is no longer in use, consider removing it.
pub UNREACHABLE_CODE,
Warn,
"detects unreachable code paths",
report_in_external_macro
}
declare_lint! {
/// The `unreachable_patterns` lint detects unreachable patterns.
///
/// ### Example
///
/// ```rust
/// let x = 5;
/// match x {
/// y => (),
/// 5 => (),
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This usually indicates a mistake in how the patterns are specified or
/// ordered. In this example, the `y` pattern will always match, so the
/// five is impossible to reach. Remember, match arms match in order, you
/// probably wanted to put the `5` case above the `y` case.
pub UNREACHABLE_PATTERNS,
Warn,
"detects unreachable patterns"
}
declare_lint! {
/// The `overlapping_range_endpoints` lint detects `match` arms that have [range patterns] that
/// overlap on their endpoints.
///
/// [range patterns]: https://doc.rust-lang.org/nightly/reference/patterns.html#range-patterns
///
/// ### Example
///
/// ```rust
/// let x = 123u8;
/// match x {
/// 0..=100 => { println!("small"); }
/// 100..=255 => { println!("large"); }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is likely a mistake to have range patterns in a match expression that overlap in this
/// way. Check that the beginning and end values are what you expect, and keep in mind that
/// with `..=` the left and right bounds are inclusive.
pub OVERLAPPING_RANGE_ENDPOINTS,
Warn,
"detects range patterns with overlapping endpoints"
}
declare_lint! {
/// The `non_contiguous_range_endpoints` lint detects likely off-by-one errors when using
/// exclusive [range patterns].
///
/// [range patterns]: https://doc.rust-lang.org/nightly/reference/patterns.html#range-patterns
///
/// ### Example
///
/// ```rust
/// let x = 123u32;
/// match x {
/// 0..100 => { println!("small"); }
/// 101..1000 => { println!("large"); }
/// _ => { println!("larger"); }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is likely a mistake to have range patterns in a match expression that miss out a single
/// number. Check that the beginning and end values are what you expect, and keep in mind that
/// with `..=` the right bound is inclusive, and with `..` it is exclusive.
pub NON_CONTIGUOUS_RANGE_ENDPOINTS,
Warn,
"detects off-by-one errors with exclusive range patterns"
}
declare_lint! {
/// The `bindings_with_variant_name` lint detects pattern bindings with
/// the same name as one of the matched variants.
///
/// ### Example
///
/// ```rust,compile_fail
/// pub enum Enum {
/// Foo,
/// Bar,
/// }
///
/// pub fn foo(x: Enum) {
/// match x {
/// Foo => {}
/// Bar => {}
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is usually a mistake to specify an enum variant name as an
/// [identifier pattern]. In the example above, the `match` arms are
/// specifying a variable name to bind the value of `x` to. The second arm
/// is ignored because the first one matches *all* values. The likely
/// intent is that the arm was intended to match on the enum variant.
///
/// Two possible solutions are:
///
/// * Specify the enum variant using a [path pattern], such as
/// `Enum::Foo`.
/// * Bring the enum variants into local scope, such as adding `use
/// Enum::*;` to the beginning of the `foo` function in the example
/// above.
///
/// [identifier pattern]: https://doc.rust-lang.org/reference/patterns.html#identifier-patterns
/// [path pattern]: https://doc.rust-lang.org/reference/patterns.html#path-patterns
pub BINDINGS_WITH_VARIANT_NAME,
Deny,
"detects pattern bindings with the same name as one of the matched variants"
}
declare_lint! {
/// The `unused_macros` lint detects macros that were not used.
///
/// Note that this lint is distinct from the `unused_macro_rules` lint,
/// which checks for single rules that never match of an otherwise used
/// macro, and thus never expand.
///
/// ### Example
///
/// ```rust
/// macro_rules! unused {
/// () => {};
/// }
///
/// fn main() {
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused macros may signal a mistake or unfinished code. To silence the
/// warning for the individual macro, prefix the name with an underscore
/// such as `_my_macro`. If you intended to export the macro to make it
/// available outside of the crate, use the [`macro_export` attribute].
///
/// [`macro_export` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
pub UNUSED_MACROS,
Warn,
"detects macros that were not used"
}
declare_lint! {
/// The `unused_macro_rules` lint detects macro rules that were not used.
///
/// Note that the lint is distinct from the `unused_macros` lint, which
/// fires if the entire macro is never called, while this lint fires for
/// single unused rules of the macro that is otherwise used.
/// `unused_macro_rules` fires only if `unused_macros` wouldn't fire.
///
/// ### Example
///
/// ```rust
/// #[warn(unused_macro_rules)]
/// macro_rules! unused_empty {
/// (hello) => { println!("Hello, world!") }; // This rule is unused
/// () => { println!("empty") }; // This rule is used
/// }
///
/// fn main() {
/// unused_empty!(hello);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused macro rules may signal a mistake or unfinished code. Furthermore,
/// they slow down compilation. Right now, silencing the warning is not
/// supported on a single rule level, so you have to add an allow to the
/// entire macro definition.
///
/// If you intended to export the macro to make it
/// available outside of the crate, use the [`macro_export` attribute].
///
/// [`macro_export` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
pub UNUSED_MACRO_RULES,
Allow,
"detects macro rules that were not used"
}
declare_lint! {
/// The `warnings` lint allows you to change the level of other
/// lints which produce warnings.
///
/// ### Example
///
/// ```rust
/// #![deny(warnings)]
/// fn foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The `warnings` lint is a bit special; by changing its level, you
/// change every other warning that would produce a warning to whatever
/// value you'd like. As such, you won't ever trigger this lint in your
/// code directly.
pub WARNINGS,
Warn,
"mass-change the level for lints which produce warnings"
}
declare_lint! {
/// The `unused_features` lint detects unused or unknown features found in
/// crate-level [`feature` attributes].
///
/// [`feature` attributes]: https://doc.rust-lang.org/nightly/unstable-book/
///
/// Note: This lint is currently not functional, see [issue #44232] for
/// more details.
///
/// [issue #44232]: https://github.com/rust-lang/rust/issues/44232
pub UNUSED_FEATURES,
Warn,
"unused features found in crate-level `#[feature]` directives"
}
declare_lint! {
/// The `stable_features` lint detects a [`feature` attribute] that
/// has since been made stable.
///
/// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
///
/// ### Example
///
/// ```rust
/// #![feature(test_accepted_feature)]
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// When a feature is stabilized, it is no longer necessary to include a
/// `#![feature]` attribute for it. To fix, simply remove the
/// `#![feature]` attribute.
pub STABLE_FEATURES,
Warn,
"stable features found in `#[feature]` directive"
}
declare_lint! {
/// The `unknown_crate_types` lint detects an unknown crate type found in
/// a [`crate_type` attribute].
///
/// ### Example
///
/// ```rust,compile_fail
/// #![crate_type="lol"]
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// An unknown value give to the `crate_type` attribute is almost
/// certainly a mistake.
///
/// [`crate_type` attribute]: https://doc.rust-lang.org/reference/linkage.html
pub UNKNOWN_CRATE_TYPES,
Deny,
"unknown crate type found in `#[crate_type]` directive",
crate_level_only
}
declare_lint! {
/// The `trivial_casts` lint detects trivial casts which could be replaced
/// with coercion, which may require a temporary variable.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(trivial_casts)]
/// let x: &u32 = &42;
/// let y = x as *const u32;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// A trivial cast is a cast `e as T` where `e` has type `U` and `U` is a
/// subtype of `T`. This type of cast is usually unnecessary, as it can be
/// usually be inferred.
///
/// This lint is "allow" by default because there are situations, such as
/// with FFI interfaces or complex type aliases, where it triggers
/// incorrectly, or in situations where it will be more difficult to
/// clearly express the intent. It may be possible that this will become a
/// warning in the future, possibly with an explicit syntax for coercions
/// providing a convenient way to work around the current issues.
/// See [RFC 401 (coercions)][rfc-401], [RFC 803 (type ascription)][rfc-803] and
/// [RFC 3307 (remove type ascription)][rfc-3307] for historical context.
///
/// [rfc-401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md
/// [rfc-803]: https://github.com/rust-lang/rfcs/blob/master/text/0803-type-ascription.md
/// [rfc-3307]: https://github.com/rust-lang/rfcs/blob/master/text/3307-de-rfc-type-ascription.md
pub TRIVIAL_CASTS,
Allow,
"detects trivial casts which could be removed"
}
declare_lint! {
/// The `trivial_numeric_casts` lint detects trivial numeric casts of types
/// which could be removed.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(trivial_numeric_casts)]
/// let x = 42_i32 as i32;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// A trivial numeric cast is a cast of a numeric type to the same numeric
/// type. This type of cast is usually unnecessary.
///
/// This lint is "allow" by default because there are situations, such as
/// with FFI interfaces or complex type aliases, where it triggers
/// incorrectly, or in situations where it will be more difficult to
/// clearly express the intent. It may be possible that this will become a
/// warning in the future, possibly with an explicit syntax for coercions
/// providing a convenient way to work around the current issues.
/// See [RFC 401 (coercions)][rfc-401], [RFC 803 (type ascription)][rfc-803] and
/// [RFC 3307 (remove type ascription)][rfc-3307] for historical context.
///
/// [rfc-401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md
/// [rfc-803]: https://github.com/rust-lang/rfcs/blob/master/text/0803-type-ascription.md
/// [rfc-3307]: https://github.com/rust-lang/rfcs/blob/master/text/3307-de-rfc-type-ascription.md
pub TRIVIAL_NUMERIC_CASTS,
Allow,
"detects trivial casts of numeric types which could be removed"
}
declare_lint! {
/// The `exported_private_dependencies` lint detects private dependencies
/// that are exposed in a public interface.
///
/// ### Example
///
/// ```rust,ignore (needs-dependency)
/// pub fn foo() -> Option<some_private_dependency::Thing> {
/// None
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// warning: type `bar::Thing` from private dependency 'bar' in public interface
/// --> src/lib.rs:3:1
/// |
/// 3 | pub fn foo() -> Option<bar::Thing> {
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// |
/// = note: `#[warn(exported_private_dependencies)]` on by default
/// ```
///
/// ### Explanation
///
/// Dependencies can be marked as "private" to indicate that they are not
/// exposed in the public interface of a crate. This can be used by Cargo
/// to independently resolve those dependencies because it can assume it
/// does not need to unify them with other packages using that same
/// dependency. This lint is an indication of a violation of that
/// contract.
///
/// To fix this, avoid exposing the dependency in your public interface.
/// Or, switch the dependency to a public dependency.
///
/// Note that support for this is only available on the nightly channel.
/// See [RFC 1977] for more details, as well as the [Cargo documentation].
///
/// [RFC 1977]: https://github.com/rust-lang/rfcs/blob/master/text/1977-public-private-dependencies.md
/// [Cargo documentation]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#public-dependency
pub EXPORTED_PRIVATE_DEPENDENCIES,
Warn,
"public interface leaks type from a private dependency"
}
declare_lint! {
/// The `pub_use_of_private_extern_crate` lint detects a specific
/// situation of re-exporting a private `extern crate`.
///
/// ### Example
///
/// ```rust,compile_fail
/// extern crate core;
/// pub use core as reexported_core;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// A public `use` declaration should not be used to publically re-export a
/// private `extern crate`. `pub extern crate` should be used instead.
///
/// This was historically allowed, but is not the intended behavior
/// according to the visibility rules. This is a [future-incompatible]
/// lint to transition this to a hard error in the future. See [issue
/// #127909] for more details.
///
/// [issue #127909]: https://github.com/rust-lang/rust/issues/127909
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub PUB_USE_OF_PRIVATE_EXTERN_CRATE,
Deny,
"detect public re-exports of private extern crates",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #127909 <https://github.com/rust-lang/rust/issues/127909>",
report_in_deps: true,
};
}
declare_lint! {
/// The `invalid_type_param_default` lint detects type parameter defaults
/// erroneously allowed in an invalid location.
///
/// ### Example
///
/// ```rust,compile_fail
/// fn foo<T=i32>(t: T) {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Default type parameters were only intended to be allowed in certain
/// situations, but historically the compiler allowed them everywhere.
/// This is a [future-incompatible] lint to transition this to a hard
/// error in the future. See [issue #36887] for more details.
///
/// [issue #36887]: https://github.com/rust-lang/rust/issues/36887
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub INVALID_TYPE_PARAM_DEFAULT,
Deny,
"type parameter default erroneously allowed in invalid location",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #36887 <https://github.com/rust-lang/rust/issues/36887>",
report_in_deps: true,
};
}
declare_lint! {
/// The `renamed_and_removed_lints` lint detects lints that have been
/// renamed or removed.
///
/// ### Example
///
/// ```rust
/// #![deny(raw_pointer_derive)]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// To fix this, either remove the lint or use the new name. This can help
/// avoid confusion about lints that are no longer valid, and help
/// maintain consistency for renamed lints.
pub RENAMED_AND_REMOVED_LINTS,
Warn,
"lints that have been renamed or removed"
}
declare_lint! {
/// The `const_item_mutation` lint detects attempts to mutate a `const`
/// item.
///
/// ### Example
///
/// ```rust
/// const FOO: [i32; 1] = [0];
///
/// fn main() {
/// FOO[0] = 1;
/// // This will print "[0]".
/// println!("{:?}", FOO);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Trying to directly mutate a `const` item is almost always a mistake.
/// What is happening in the example above is that a temporary copy of the
/// `const` is mutated, but the original `const` is not. Each time you
/// refer to the `const` by name (such as `FOO` in the example above), a
/// separate copy of the value is inlined at that location.
///
/// This lint checks for writing directly to a field (`FOO.field =
/// some_value`) or array entry (`FOO[0] = val`), or taking a mutable
/// reference to the const item (`&mut FOO`), including through an
/// autoderef (`FOO.some_mut_self_method()`).
///
/// There are various alternatives depending on what you are trying to
/// accomplish:
///
/// * First, always reconsider using mutable globals, as they can be
/// difficult to use correctly, and can make the code more difficult to
/// use or understand.
/// * If you are trying to perform a one-time initialization of a global:
/// * If the value can be computed at compile-time, consider using
/// const-compatible values (see [Constant Evaluation]).
/// * For more complex single-initialization cases, consider using
/// [`std::sync::LazyLock`].
/// * If you truly need a mutable global, consider using a [`static`],
/// which has a variety of options:
/// * Simple data types can be directly defined and mutated with an
/// [`atomic`] type.
/// * More complex types can be placed in a synchronization primitive
/// like a [`Mutex`], which can be initialized with one of the options
/// listed above.
/// * A [mutable `static`] is a low-level primitive, requiring unsafe.
/// Typically This should be avoided in preference of something
/// higher-level like one of the above.
///
/// [Constant Evaluation]: https://doc.rust-lang.org/reference/const_eval.html
/// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
/// [mutable `static`]: https://doc.rust-lang.org/reference/items/static-items.html#mutable-statics
/// [`std::sync::LazyLock`]: https://doc.rust-lang.org/stable/std/sync/struct.LazyLock.html
/// [`atomic`]: https://doc.rust-lang.org/std/sync/atomic/index.html
/// [`Mutex`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html
pub CONST_ITEM_MUTATION,
Warn,
"detects attempts to mutate a `const` item",
}
declare_lint! {
/// The `patterns_in_fns_without_body` lint detects `mut` identifier
/// patterns as a parameter in functions without a body.
///
/// ### Example
///
/// ```rust,compile_fail
/// trait Trait {
/// fn foo(mut arg: u8);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// To fix this, remove `mut` from the parameter in the trait definition;
/// it can be used in the implementation. That is, the following is OK:
///
/// ```rust
/// trait Trait {
/// fn foo(arg: u8); // Removed `mut` here
/// }
///
/// impl Trait for i32 {
/// fn foo(mut arg: u8) { // `mut` here is OK
///
/// }
/// }
/// ```
///
/// Trait definitions can define functions without a body to specify a
/// function that implementors must define. The parameter names in the
/// body-less functions are only allowed to be `_` or an [identifier] for
/// documentation purposes (only the type is relevant). Previous versions
/// of the compiler erroneously allowed [identifier patterns] with the
/// `mut` keyword, but this was not intended to be allowed. This is a
/// [future-incompatible] lint to transition this to a hard error in the
/// future. See [issue #35203] for more details.
///
/// [identifier]: https://doc.rust-lang.org/reference/identifiers.html
/// [identifier patterns]: https://doc.rust-lang.org/reference/patterns.html#identifier-patterns
/// [issue #35203]: https://github.com/rust-lang/rust/issues/35203
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub PATTERNS_IN_FNS_WITHOUT_BODY,
Deny,
"patterns in functions without body were erroneously allowed",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #35203 <https://github.com/rust-lang/rust/issues/35203>",
};
}
declare_lint! {
/// The `late_bound_lifetime_arguments` lint detects generic lifetime
/// arguments in path segments with late bound lifetime parameters.
///
/// ### Example
///
/// ```rust
/// struct S;
///
/// impl S {
/// fn late(self, _: &u8, _: &u8) {}
/// }
///
/// fn main() {
/// S.late::<'static>(&0, &0);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is not clear how to provide arguments for early-bound lifetime
/// parameters if they are intermixed with late-bound parameters in the
/// same list. For now, providing any explicit arguments will trigger this
/// lint if late-bound parameters are present, so in the future a solution
/// can be adopted without hitting backward compatibility issues. This is
/// a [future-incompatible] lint to transition this to a hard error in the
/// future. See [issue #42868] for more details, along with a description
/// of the difference between early and late-bound parameters.
///
/// [issue #42868]: https://github.com/rust-lang/rust/issues/42868
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub LATE_BOUND_LIFETIME_ARGUMENTS,
Warn,
"detects generic lifetime arguments in path segments with late bound lifetime parameters",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #42868 <https://github.com/rust-lang/rust/issues/42868>",
};
}
declare_lint! {
/// The `coherence_leak_check` lint detects conflicting implementations of
/// a trait that are only distinguished by the old leak-check code.
///
/// ### Example
///
/// ```rust
/// trait SomeTrait { }
/// impl SomeTrait for for<'a> fn(&'a u8) { }
/// impl<'a> SomeTrait for fn(&'a u8) { }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In the past, the compiler would accept trait implementations for
/// identical functions that differed only in where the lifetime binder
/// appeared. Due to a change in the borrow checker implementation to fix
/// several bugs, this is no longer allowed. However, since this affects
/// existing code, this is a [future-incompatible] lint to transition this
/// to a hard error in the future.
///
/// Code relying on this pattern should introduce "[newtypes]",
/// like `struct Foo(for<'a> fn(&'a u8))`.
///
/// See [issue #56105] for more details.
///
/// [issue #56105]: https://github.com/rust-lang/rust/issues/56105
/// [newtypes]: https://doc.rust-lang.org/book/ch19-04-advanced-types.html#using-the-newtype-pattern-for-type-safety-and-abstraction
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub COHERENCE_LEAK_CHECK,
Warn,
"distinct impls distinguished only by the leak-check code",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::Custom("the behavior may change in a future release"),
reference: "issue #56105 <https://github.com/rust-lang/rust/issues/56105>",
};
}
declare_lint! {
/// The `deprecated` lint detects use of deprecated items.
///
/// ### Example
///
/// ```rust
/// #[deprecated]
/// fn foo() {}
///
/// fn bar() {
/// foo();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Items may be marked "deprecated" with the [`deprecated` attribute] to
/// indicate that they should no longer be used. Usually the attribute
/// should include a note on what to use instead, or check the
/// documentation.
///
/// [`deprecated` attribute]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-deprecated-attribute
pub DEPRECATED,
Warn,
"detects use of deprecated items",
report_in_external_macro
}
declare_lint! {
/// The `unused_unsafe` lint detects unnecessary use of an `unsafe` block.
///
/// ### Example
///
/// ```rust
/// unsafe {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// If nothing within the block requires `unsafe`, then remove the
/// `unsafe` marker because it is not required and may cause confusion.
pub UNUSED_UNSAFE,
Warn,
"unnecessary use of an `unsafe` block"
}
declare_lint! {
/// The `unused_mut` lint detects mut variables which don't need to be
/// mutable.
///
/// ### Example
///
/// ```rust
/// let mut x = 5;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The preferred style is to only mark variables as `mut` if it is
/// required.
pub UNUSED_MUT,
Warn,
"detect mut variables which don't need to be mutable"
}
declare_lint! {
/// The `rust_2024_incompatible_pat` lint
/// detects patterns whose meaning will change in the Rust 2024 edition.
///
/// ### Example
///
/// ```rust,edition2021
/// #![warn(rust_2024_incompatible_pat)]
///
/// if let Some(&a) = &Some(&0u8) {
/// let _: u8 = a;
/// }
/// if let Some(mut _a) = &mut Some(0u8) {
/// _a = 7u8;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In Rust 2024 and above, the `mut` keyword does not reset the pattern binding mode,
/// and nor do `&` or `&mut` patterns. The lint will suggest code that
/// has the same meaning in all editions.
pub RUST_2024_INCOMPATIBLE_PAT,
Allow,
"detects patterns whose meaning will change in Rust 2024",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2024),
reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>",
};
}
declare_lint! {
/// The `unconditional_recursion` lint detects functions that cannot
/// return without calling themselves.
///
/// ### Example
///
/// ```rust
/// fn foo() {
/// foo();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is usually a mistake to have a recursive call that does not have
/// some condition to cause it to terminate. If you really intend to have
/// an infinite loop, using a `loop` expression is recommended.
pub UNCONDITIONAL_RECURSION,
Warn,
"functions that cannot return without calling themselves"
}
declare_lint! {
/// The `single_use_lifetimes` lint detects lifetimes that are only used
/// once.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(single_use_lifetimes)]
///
/// fn foo<'a>(x: &'a u32) {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Specifying an explicit lifetime like `'a` in a function or `impl`
/// should only be used to link together two things. Otherwise, you should
/// just use `'_` to indicate that the lifetime is not linked to anything,
/// or elide the lifetime altogether if possible.
///
/// This lint is "allow" by default because it was introduced at a time
/// when `'_` and elided lifetimes were first being introduced, and this
/// lint would be too noisy. Also, there are some known false positives
/// that it produces. See [RFC 2115] for historical context, and [issue
/// #44752] for more details.
///
/// [RFC 2115]: https://github.com/rust-lang/rfcs/blob/master/text/2115-argument-lifetimes.md
/// [issue #44752]: https://github.com/rust-lang/rust/issues/44752
pub SINGLE_USE_LIFETIMES,
Allow,
"detects lifetime parameters that are only used once"
}
declare_lint! {
/// The `unused_lifetimes` lint detects lifetime parameters that are never
/// used.
///
/// ### Example
///
/// ```rust,compile_fail
/// #[deny(unused_lifetimes)]
///
/// pub fn foo<'a>() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused lifetime parameters may signal a mistake or unfinished code.
/// Consider removing the parameter.
pub UNUSED_LIFETIMES,
Allow,
"detects lifetime parameters that are never used"
}
declare_lint! {
/// The `redundant_lifetimes` lint detects lifetime parameters that are
/// redundant because they are equal to another named lifetime.
///
/// ### Example
///
/// ```rust,compile_fail
/// #[deny(redundant_lifetimes)]
///
/// // `'a = 'static`, so all usages of `'a` can be replaced with `'static`
/// pub fn bar<'a: 'static>() {}
///
/// // `'a = 'b`, so all usages of `'b` can be replaced with `'a`
/// pub fn bar<'a: 'b, 'b: 'a>() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused lifetime parameters may signal a mistake or unfinished code.
/// Consider removing the parameter.
pub REDUNDANT_LIFETIMES,
Allow,
"detects lifetime parameters that are redundant because they are equal to some other named lifetime"
}
declare_lint! {
/// The `tyvar_behind_raw_pointer` lint detects raw pointer to an
/// inference variable.
///
/// ### Example
///
/// ```rust,edition2015
/// // edition 2015
/// let data = std::ptr::null();
/// let _ = &data as *const *const ();
///
/// if data.is_null() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This kind of inference was previously allowed, but with the future
/// arrival of [arbitrary self types], this can introduce ambiguity. To
/// resolve this, use an explicit type instead of relying on type
/// inference.
///
/// This is a [future-incompatible] lint to transition this to a hard
/// error in the 2018 edition. See [issue #46906] for more details. This
/// is currently a hard-error on the 2018 edition, and is "warn" by
/// default in the 2015 edition.
///
/// [arbitrary self types]: https://github.com/rust-lang/rust/issues/44874
/// [issue #46906]: https://github.com/rust-lang/rust/issues/46906
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub TYVAR_BEHIND_RAW_POINTER,
Warn,
"raw pointer to an inference variable",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
reference: "issue #46906 <https://github.com/rust-lang/rust/issues/46906>",
};
}
declare_lint! {
/// The `elided_lifetimes_in_paths` lint detects the use of hidden
/// lifetime parameters.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(elided_lifetimes_in_paths)]
/// #![deny(warnings)]
/// struct Foo<'a> {
/// x: &'a u32
/// }
///
/// fn foo(x: &Foo) {
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Elided lifetime parameters can make it difficult to see at a glance
/// that borrowing is occurring. This lint ensures that lifetime
/// parameters are always explicitly stated, even if it is the `'_`
/// [placeholder lifetime].
///
/// This lint is "allow" by default because it has some known issues, and
/// may require a significant transition for old code.
///
/// [placeholder lifetime]: https://doc.rust-lang.org/reference/lifetime-elision.html#lifetime-elision-in-functions
pub ELIDED_LIFETIMES_IN_PATHS,
Allow,
"hidden lifetime parameters in types are deprecated"
}
declare_lint! {
/// The `bare_trait_objects` lint suggests using `dyn Trait` for trait
/// objects.
///
/// ### Example
///
/// ```rust,edition2018
/// trait Trait { }
///
/// fn takes_trait_object(_: Box<Trait>) {
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Without the `dyn` indicator, it can be ambiguous or confusing when
/// reading code as to whether or not you are looking at a trait object.
/// The `dyn` keyword makes it explicit, and adds a symmetry to contrast
/// with [`impl Trait`].
///
/// [`impl Trait`]: https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters
pub BARE_TRAIT_OBJECTS,
Warn,
"suggest using `dyn Trait` for trait objects",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2021/warnings-promoted-to-error.html>",
};
}
declare_lint! {
/// The `absolute_paths_not_starting_with_crate` lint detects fully
/// qualified paths that start with a module name instead of `crate`,
/// `self`, or an extern crate name
///
/// ### Example
///
/// ```rust,edition2015,compile_fail
/// #![deny(absolute_paths_not_starting_with_crate)]
///
/// mod foo {
/// pub fn bar() {}
/// }
///
/// fn main() {
/// ::foo::bar();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Rust [editions] allow the language to evolve without breaking
/// backwards compatibility. This lint catches code that uses absolute
/// paths in the style of the 2015 edition. In the 2015 edition, absolute
/// paths (those starting with `::`) refer to either the crate root or an
/// external crate. In the 2018 edition it was changed so that they only
/// refer to external crates. The path prefix `crate::` should be used
/// instead to reference items from the crate root.
///
/// If you switch the compiler from the 2015 to 2018 edition without
/// updating the code, then it will fail to compile if the old style paths
/// are used. You can manually change the paths to use the `crate::`
/// prefix to transition to the 2018 edition.
///
/// This lint solves the problem automatically. It is "allow" by default
/// because the code is perfectly valid in the 2015 edition. The [`cargo
/// fix`] tool with the `--edition` flag will switch this lint to "warn"
/// and automatically apply the suggested fix from the compiler. This
/// provides a completely automated way to update old code to the 2018
/// edition.
///
/// [editions]: https://doc.rust-lang.org/edition-guide/
/// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
pub ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
Allow,
"fully qualified paths that start with a module name \
instead of `crate`, `self`, or an extern crate name",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
reference: "issue #53130 <https://github.com/rust-lang/rust/issues/53130>",
};
}
declare_lint! {
/// The `unstable_name_collisions` lint detects that you have used a name
/// that the standard library plans to add in the future.
///
/// ### Example
///
/// ```rust
/// trait MyIterator : Iterator {
/// // is_partitioned is an unstable method that already exists on the Iterator trait
/// fn is_partitioned<P>(self, predicate: P) -> bool
/// where
/// Self: Sized,
/// P: FnMut(Self::Item) -> bool,
/// {true}
/// }
///
/// impl<T: ?Sized> MyIterator for T where T: Iterator { }
///
/// let x = vec![1, 2, 3];
/// let _ = x.iter().is_partitioned(|_| true);
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// When new methods are added to traits in the standard library, they are
/// usually added in an "unstable" form which is only available on the
/// [nightly channel] with a [`feature` attribute]. If there is any
/// preexisting code which extends a trait to have a method with the same
/// name, then the names will collide. In the future, when the method is
/// stabilized, this will cause an error due to the ambiguity. This lint
/// is an early-warning to let you know that there may be a collision in
/// the future. This can be avoided by adding type annotations to
/// disambiguate which trait method you intend to call, such as
/// `MyIterator::is_partitioned(my_iter, my_predicate)` or renaming or removing the method.
///
/// [nightly channel]: https://doc.rust-lang.org/book/appendix-07-nightly-rust.html
/// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
pub UNSTABLE_NAME_COLLISIONS,
Warn,
"detects name collision with an existing but unstable method",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::Custom(
"once this associated item is added to the standard library, \
the ambiguity may cause an error or change in behavior!"
),
reference: "issue #48919 <https://github.com/rust-lang/rust/issues/48919>",
// Note: this item represents future incompatibility of all unstable functions in the
// standard library, and thus should never be removed or changed to an error.
};
}
declare_lint! {
/// The `irrefutable_let_patterns` lint detects [irrefutable patterns]
/// in [`if let`]s, [`while let`]s, and `if let` guards.
///
/// ### Example
///
/// ```rust
/// if let _ = 123 {
/// println!("always runs!");
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// There usually isn't a reason to have an irrefutable pattern in an
/// `if let` or `while let` statement, because the pattern will always match
/// successfully. A [`let`] or [`loop`] statement will suffice. However,
/// when generating code with a macro, forbidding irrefutable patterns
/// would require awkward workarounds in situations where the macro
/// doesn't know if the pattern is refutable or not. This lint allows
/// macros to accept this form, while alerting for a possibly incorrect
/// use in normal code.
///
/// See [RFC 2086] for more details.
///
/// [irrefutable patterns]: https://doc.rust-lang.org/reference/patterns.html#refutability
/// [`if let`]: https://doc.rust-lang.org/reference/expressions/if-expr.html#if-let-expressions
/// [`while let`]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#predicate-pattern-loops
/// [`let`]: https://doc.rust-lang.org/reference/statements.html#let-statements
/// [`loop`]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#infinite-loops
/// [RFC 2086]: https://github.com/rust-lang/rfcs/blob/master/text/2086-allow-if-let-irrefutables.md
pub IRREFUTABLE_LET_PATTERNS,
Warn,
"detects irrefutable patterns in `if let` and `while let` statements"
}
declare_lint! {
/// The `unused_labels` lint detects [labels] that are never used.
///
/// [labels]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#loop-labels
///
/// ### Example
///
/// ```rust,no_run
/// 'unused_label: loop {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused labels may signal a mistake or unfinished code. To silence the
/// warning for the individual label, prefix it with an underscore such as
/// `'_my_label:`.
pub UNUSED_LABELS,
Warn,
"detects labels that are never used"
}
declare_lint! {
/// The `proc_macro_derive_resolution_fallback` lint detects proc macro
/// derives using inaccessible names from parent modules.
///
/// ### Example
///
/// ```rust,ignore (proc-macro)
/// // foo.rs
/// #![crate_type = "proc-macro"]
///
/// extern crate proc_macro;
///
/// use proc_macro::*;
///
/// #[proc_macro_derive(Foo)]
/// pub fn foo1(a: TokenStream) -> TokenStream {
/// drop(a);
/// "mod __bar { static mut BAR: Option<Something> = None; }".parse().unwrap()
/// }
/// ```
///
/// ```rust,ignore (needs-dependency)
/// // bar.rs
/// #[macro_use]
/// extern crate foo;
///
/// struct Something;
///
/// #[derive(Foo)]
/// struct Another;
///
/// fn main() {}
/// ```
///
/// This will produce:
///
/// ```text
/// warning: cannot find type `Something` in this scope
/// --> src/main.rs:8:10
/// |
/// 8 | #[derive(Foo)]
/// | ^^^ names from parent modules are not accessible without an explicit import
/// |
/// = note: `#[warn(proc_macro_derive_resolution_fallback)]` on by default
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #50504 <https://github.com/rust-lang/rust/issues/50504>
/// ```
///
/// ### Explanation
///
/// If a proc-macro generates a module, the compiler unintentionally
/// allowed items in that module to refer to items in the crate root
/// without importing them. This is a [future-incompatible] lint to
/// transition this to a hard error in the future. See [issue #50504] for
/// more details.
///
/// [issue #50504]: https://github.com/rust-lang/rust/issues/50504
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
Deny,
"detects proc macro derives using inaccessible names from parent modules",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #83583 <https://github.com/rust-lang/rust/issues/83583>",
report_in_deps: true,
};
}
declare_lint! {
/// The `macro_use_extern_crate` lint detects the use of the [`macro_use` attribute].
///
/// ### Example
///
/// ```rust,ignore (needs extern crate)
/// #![deny(macro_use_extern_crate)]
///
/// #[macro_use]
/// extern crate serde_json;
///
/// fn main() {
/// let _ = json!{{}};
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// error: applying the `#[macro_use]` attribute to an `extern crate` item is deprecated
/// --> src/main.rs:3:1
/// |
/// 3 | #[macro_use]
/// | ^^^^^^^^^^^^
/// |
/// = help: remove it and import macros at use sites with a `use` item instead
/// note: the lint level is defined here
/// --> src/main.rs:1:9
/// |
/// 1 | #![deny(macro_use_extern_crate)]
/// | ^^^^^^^^^^^^^^^^^^^^^^
/// ```
///
/// ### Explanation
///
/// The [`macro_use` attribute] on an [`extern crate`] item causes
/// macros in that external crate to be brought into the prelude of the
/// crate, making the macros in scope everywhere. As part of the efforts
/// to simplify handling of dependencies in the [2018 edition], the use of
/// `extern crate` is being phased out. To bring macros from extern crates
/// into scope, it is recommended to use a [`use` import].
///
/// This lint is "allow" by default because this is a stylistic choice
/// that has not been settled, see [issue #52043] for more information.
///
/// [`macro_use` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#the-macro_use-attribute
/// [`use` import]: https://doc.rust-lang.org/reference/items/use-declarations.html
/// [issue #52043]: https://github.com/rust-lang/rust/issues/52043
pub MACRO_USE_EXTERN_CRATE,
Allow,
"the `#[macro_use]` attribute is now deprecated in favor of using macros \
via the module system"
}
declare_lint! {
/// The `macro_expanded_macro_exports_accessed_by_absolute_paths` lint
/// detects macro-expanded [`macro_export`] macros from the current crate
/// that cannot be referred to by absolute paths.
///
/// [`macro_export`]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
///
/// ### Example
///
/// ```rust,compile_fail
/// macro_rules! define_exported {
/// () => {
/// #[macro_export]
/// macro_rules! exported {
/// () => {};
/// }
/// };
/// }
///
/// define_exported!();
///
/// fn main() {
/// crate::exported!();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The intent is that all macros marked with the `#[macro_export]`
/// attribute are made available in the root of the crate. However, when a
/// `macro_rules!` definition is generated by another macro, the macro
/// expansion is unable to uphold this rule. This is a
/// [future-incompatible] lint to transition this to a hard error in the
/// future. See [issue #53495] for more details.
///
/// [issue #53495]: https://github.com/rust-lang/rust/issues/53495
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
Deny,
"macro-expanded `macro_export` macros from the current crate \
cannot be referred to by absolute paths",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #52234 <https://github.com/rust-lang/rust/issues/52234>",
report_in_deps: true,
};
crate_level_only
}
declare_lint! {
/// The `explicit_outlives_requirements` lint detects unnecessary
/// lifetime bounds that can be inferred.
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![allow(unused)]
/// #![deny(explicit_outlives_requirements)]
/// #![deny(warnings)]
///
/// struct SharedRef<'a, T>
/// where
/// T: 'a,
/// {
/// data: &'a T,
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// If a `struct` contains a reference, such as `&'a T`, the compiler
/// requires that `T` outlives the lifetime `'a`. This historically
/// required writing an explicit lifetime bound to indicate this
/// requirement. However, this can be overly explicit, causing clutter and
/// unnecessary complexity. The language was changed to automatically
/// infer the bound if it is not specified. Specifically, if the struct
/// contains a reference, directly or indirectly, to `T` with lifetime
/// `'x`, then it will infer that `T: 'x` is a requirement.
///
/// This lint is "allow" by default because it can be noisy for existing
/// code that already had these requirements. This is a stylistic choice,
/// as it is still valid to explicitly state the bound. It also has some
/// false positives that can cause confusion.
///
/// See [RFC 2093] for more details.
///
/// [RFC 2093]: https://github.com/rust-lang/rfcs/blob/master/text/2093-infer-outlives.md
pub EXPLICIT_OUTLIVES_REQUIREMENTS,
Allow,
"outlives requirements can be inferred"
}
declare_lint! {
/// The `deprecated_in_future` lint is internal to rustc and should not be
/// used by user code.
///
/// This lint is only enabled in the standard library. It works with the
/// use of `#[deprecated]` with a `since` field of a version in the future.
/// This allows something to be marked as deprecated in a future version,
/// and then this lint will ensure that the item is no longer used in the
/// standard library. See the [stability documentation] for more details.
///
/// [stability documentation]: https://rustc-dev-guide.rust-lang.org/stability.html#deprecated
pub DEPRECATED_IN_FUTURE,
Allow,
"detects use of items that will be deprecated in a future version",
report_in_external_macro
}
declare_lint! {
/// The `ambiguous_associated_items` lint detects ambiguity between
/// [associated items] and [enum variants].
///
/// [associated items]: https://doc.rust-lang.org/reference/items/associated-items.html
/// [enum variants]: https://doc.rust-lang.org/reference/items/enumerations.html
///
/// ### Example
///
/// ```rust,compile_fail
/// enum E {
/// V
/// }
///
/// trait Tr {
/// type V;
/// fn foo() -> Self::V;
/// }
///
/// impl Tr for E {
/// type V = u8;
/// // `Self::V` is ambiguous because it may refer to the associated type or
/// // the enum variant.
/// fn foo() -> Self::V { 0 }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous versions of Rust did not allow accessing enum variants
/// through [type aliases]. When this ability was added (see [RFC 2338]), this
/// introduced some situations where it can be ambiguous what a type
/// was referring to.
///
/// To fix this ambiguity, you should use a [qualified path] to explicitly
/// state which type to use. For example, in the above example the
/// function can be written as `fn f() -> <Self as Tr>::V { 0 }` to
/// specifically refer to the associated type.
///
/// This is a [future-incompatible] lint to transition this to a hard
/// error in the future. See [issue #57644] for more details.
///
/// [issue #57644]: https://github.com/rust-lang/rust/issues/57644
/// [type aliases]: https://doc.rust-lang.org/reference/items/type-aliases.html#type-aliases
/// [RFC 2338]: https://github.com/rust-lang/rfcs/blob/master/text/2338-type-alias-enum-variants.md
/// [qualified path]: https://doc.rust-lang.org/reference/paths.html#qualified-paths
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub AMBIGUOUS_ASSOCIATED_ITEMS,
Deny,
"ambiguous associated items",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #57644 <https://github.com/rust-lang/rust/issues/57644>",
};
}
declare_lint! {
/// The `soft_unstable` lint detects unstable features that were unintentionally allowed on
/// stable. This is a [future-incompatible] lint to transition this to a hard error in the
/// future. See [issue #64266] for more details.
///
/// [issue #64266]: https://github.com/rust-lang/rust/issues/64266
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub SOFT_UNSTABLE,
Deny,
"a feature gate that doesn't break dependent crates",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #64266 <https://github.com/rust-lang/rust/issues/64266>",
report_in_deps: true,
};
}
declare_lint! {
/// The `inline_no_sanitize` lint detects incompatible use of
/// [`#[inline(always)]`][inline] and [`#[no_sanitize(...)]`][no_sanitize].
///
/// [inline]: https://doc.rust-lang.org/reference/attributes/codegen.html#the-inline-attribute
/// [no_sanitize]: https://doc.rust-lang.org/nightly/unstable-book/language-features/no-sanitize.html
///
/// ### Example
///
/// ```rust
/// #![feature(no_sanitize)]
///
/// #[inline(always)]
/// #[no_sanitize(address)]
/// fn x() {}
///
/// fn main() {
/// x()
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The use of the [`#[inline(always)]`][inline] attribute prevents the
/// the [`#[no_sanitize(...)]`][no_sanitize] attribute from working.
/// Consider temporarily removing `inline` attribute.
pub INLINE_NO_SANITIZE,
Warn,
"detects incompatible use of `#[inline(always)]` and `#[no_sanitize(...)]`",
}
declare_lint! {
/// The `asm_sub_register` lint detects using only a subset of a register
/// for inline asm inputs.
///
/// ### Example
///
/// ```rust,ignore (fails on non-x86_64)
/// #[cfg(target_arch="x86_64")]
/// use std::arch::asm;
///
/// fn main() {
/// #[cfg(target_arch="x86_64")]
/// unsafe {
/// asm!("mov {0}, {0}", in(reg) 0i16);
/// }
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// warning: formatting may not be suitable for sub-register argument
/// --> src/main.rs:7:19
/// |
/// 7 | asm!("mov {0}, {0}", in(reg) 0i16);
/// | ^^^ ^^^ ---- for this argument
/// |
/// = note: `#[warn(asm_sub_register)]` on by default
/// = help: use the `x` modifier to have the register formatted as `ax`
/// = help: or use the `r` modifier to keep the default formatting of `rax`
/// ```
///
/// ### Explanation
///
/// Registers on some architectures can use different names to refer to a
/// subset of the register. By default, the compiler will use the name for
/// the full register size. To explicitly use a subset of the register,
/// you can override the default by using a modifier on the template
/// string operand to specify when subregister to use. This lint is issued
/// if you pass in a value with a smaller data type than the default
/// register size, to alert you of possibly using the incorrect width. To
/// fix this, add the suggested modifier to the template, or cast the
/// value to the correct size.
///
/// See [register template modifiers] in the reference for more details.
///
/// [register template modifiers]: https://doc.rust-lang.org/nightly/reference/inline-assembly.html#template-modifiers
pub ASM_SUB_REGISTER,
Warn,
"using only a subset of a register for inline asm inputs",
}
declare_lint! {
/// The `bad_asm_style` lint detects the use of the `.intel_syntax` and
/// `.att_syntax` directives.
///
/// ### Example
///
/// ```rust,ignore (fails on non-x86_64)
/// #[cfg(target_arch="x86_64")]
/// use std::arch::asm;
///
/// fn main() {
/// #[cfg(target_arch="x86_64")]
/// unsafe {
/// asm!(
/// ".att_syntax",
/// "movq %{0}, %{0}", in(reg) 0usize
/// );
/// }
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// warning: avoid using `.att_syntax`, prefer using `options(att_syntax)` instead
/// --> src/main.rs:8:14
/// |
/// 8 | ".att_syntax",
/// | ^^^^^^^^^^^
/// |
/// = note: `#[warn(bad_asm_style)]` on by default
/// ```
///
/// ### Explanation
///
/// On x86, `asm!` uses the intel assembly syntax by default. While this
/// can be switched using assembler directives like `.att_syntax`, using the
/// `att_syntax` option is recommended instead because it will also properly
/// prefix register placeholders with `%` as required by AT&T syntax.
pub BAD_ASM_STYLE,
Warn,
"incorrect use of inline assembly",
}
declare_lint! {
/// The `unsafe_op_in_unsafe_fn` lint detects unsafe operations in unsafe
/// functions without an explicit unsafe block.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(unsafe_op_in_unsafe_fn)]
///
/// unsafe fn foo() {}
///
/// unsafe fn bar() {
/// foo();
/// }
///
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Currently, an [`unsafe fn`] allows any [unsafe] operation within its
/// body. However, this can increase the surface area of code that needs
/// to be scrutinized for proper behavior. The [`unsafe` block] provides a
/// convenient way to make it clear exactly which parts of the code are
/// performing unsafe operations. In the future, it is desired to change
/// it so that unsafe operations cannot be performed in an `unsafe fn`
/// without an `unsafe` block.
///
/// The fix to this is to wrap the unsafe code in an `unsafe` block.
///
/// This lint is "allow" by default on editions up to 2021, from 2024 it is
/// "warn" by default; the plan for increasing severity further is
/// still being considered. See [RFC #2585] and [issue #71668] for more
/// details.
///
/// [`unsafe fn`]: https://doc.rust-lang.org/reference/unsafe-functions.html
/// [`unsafe` block]: https://doc.rust-lang.org/reference/expressions/block-expr.html#unsafe-blocks
/// [unsafe]: https://doc.rust-lang.org/reference/unsafety.html
/// [RFC #2585]: https://github.com/rust-lang/rfcs/blob/master/text/2585-unsafe-block-in-unsafe-fn.md
/// [issue #71668]: https://github.com/rust-lang/rust/issues/71668
pub UNSAFE_OP_IN_UNSAFE_FN,
Allow,
"unsafe operations in unsafe functions without an explicit unsafe block are deprecated",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2024),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-op-in-unsafe-fn.html>",
explain_reason: false
};
@edition Edition2024 => Warn;
}
declare_lint! {
/// The `fuzzy_provenance_casts` lint detects an `as` cast between an integer
/// and a pointer.
///
/// ### Example
///
/// ```rust
/// #![feature(strict_provenance_lints)]
/// #![warn(fuzzy_provenance_casts)]
///
/// fn main() {
/// let _dangling = 16_usize as *const u8;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This lint is part of the strict provenance effort, see [issue #95228].
/// Casting an integer to a pointer is considered bad style, as a pointer
/// contains, besides the *address* also a *provenance*, indicating what
/// memory the pointer is allowed to read/write. Casting an integer, which
/// doesn't have provenance, to a pointer requires the compiler to assign
/// (guess) provenance. The compiler assigns "all exposed valid" (see the
/// docs of [`ptr::with_exposed_provenance`] for more information about this
/// "exposing"). This penalizes the optimiser and is not well suited for
/// dynamic analysis/dynamic program verification (e.g. Miri or CHERI
/// platforms).
///
/// It is much better to use [`ptr::with_addr`] instead to specify the
/// provenance you want. If using this function is not possible because the
/// code relies on exposed provenance then there is as an escape hatch
/// [`ptr::with_exposed_provenance`].
///
/// [issue #95228]: https://github.com/rust-lang/rust/issues/95228
/// [`ptr::with_addr`]: https://doc.rust-lang.org/core/primitive.pointer.html#method.with_addr
/// [`ptr::with_exposed_provenance`]: https://doc.rust-lang.org/core/ptr/fn.with_exposed_provenance.html
pub FUZZY_PROVENANCE_CASTS,
Allow,
"a fuzzy integer to pointer cast is used",
@feature_gate = strict_provenance_lints;
}
declare_lint! {
/// The `lossy_provenance_casts` lint detects an `as` cast between a pointer
/// and an integer.
///
/// ### Example
///
/// ```rust
/// #![feature(strict_provenance_lints)]
/// #![warn(lossy_provenance_casts)]
///
/// fn main() {
/// let x: u8 = 37;
/// let _addr: usize = &x as *const u8 as usize;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This lint is part of the strict provenance effort, see [issue #95228].
/// Casting a pointer to an integer is a lossy operation, because beyond
/// just an *address* a pointer may be associated with a particular
/// *provenance*. This information is used by the optimiser and for dynamic
/// analysis/dynamic program verification (e.g. Miri or CHERI platforms).
///
/// Since this cast is lossy, it is considered good style to use the
/// [`ptr::addr`] method instead, which has a similar effect, but doesn't
/// "expose" the pointer provenance. This improves optimisation potential.
/// See the docs of [`ptr::addr`] and [`ptr::expose_provenance`] for more information
/// about exposing pointer provenance.
///
/// If your code can't comply with strict provenance and needs to expose
/// the provenance, then there is [`ptr::expose_provenance`] as an escape hatch,
/// which preserves the behaviour of `as usize` casts while being explicit
/// about the semantics.
///
/// [issue #95228]: https://github.com/rust-lang/rust/issues/95228
/// [`ptr::addr`]: https://doc.rust-lang.org/core/primitive.pointer.html#method.addr
/// [`ptr::expose_provenance`]: https://doc.rust-lang.org/core/primitive.pointer.html#method.expose_provenance
pub LOSSY_PROVENANCE_CASTS,
Allow,
"a lossy pointer to integer cast is used",
@feature_gate = strict_provenance_lints;
}
declare_lint! {
/// The `const_evaluatable_unchecked` lint detects a generic constant used
/// in a type.
///
/// ### Example
///
/// ```rust
/// const fn foo<T>() -> usize {
/// if size_of::<*mut T>() < 8 { // size of *mut T does not depend on T
/// 4
/// } else {
/// 8
/// }
/// }
///
/// fn test<T>() {
/// let _ = [0; foo::<T>()];
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In the 1.43 release, some uses of generic parameters in array repeat
/// expressions were accidentally allowed. This is a [future-incompatible]
/// lint to transition this to a hard error in the future. See [issue
/// #76200] for a more detailed description and possible fixes.
///
/// [future-incompatible]: ../index.md#future-incompatible-lints
/// [issue #76200]: https://github.com/rust-lang/rust/issues/76200
pub CONST_EVALUATABLE_UNCHECKED,
Warn,
"detects a generic constant is used in a type without a emitting a warning",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #76200 <https://github.com/rust-lang/rust/issues/76200>",
};
}
declare_lint! {
/// The `function_item_references` lint detects function references that are
/// formatted with [`fmt::Pointer`] or transmuted.
///
/// [`fmt::Pointer`]: https://doc.rust-lang.org/std/fmt/trait.Pointer.html
///
/// ### Example
///
/// ```rust
/// fn foo() { }
///
/// fn main() {
/// println!("{:p}", &foo);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Taking a reference to a function may be mistaken as a way to obtain a
/// pointer to that function. This can give unexpected results when
/// formatting the reference as a pointer or transmuting it. This lint is
/// issued when function references are formatted as pointers, passed as
/// arguments bound by [`fmt::Pointer`] or transmuted.
pub FUNCTION_ITEM_REFERENCES,
Warn,
"suggest casting to a function pointer when attempting to take references to function items",
}
declare_lint! {
/// The `uninhabited_static` lint detects uninhabited statics.
///
/// ### Example
///
/// ```rust
/// enum Void {}
/// unsafe extern {
/// static EXTERN: Void;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Statics with an uninhabited type can never be initialized, so they are impossible to define.
/// However, this can be side-stepped with an `extern static`, leading to problems later in the
/// compiler which assumes that there are no initialized uninhabited places (such as locals or
/// statics). This was accidentally allowed, but is being phased out.
pub UNINHABITED_STATIC,
Warn,
"uninhabited static",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #74840 <https://github.com/rust-lang/rust/issues/74840>",
};
}
declare_lint! {
/// The `unnameable_test_items` lint detects [`#[test]`][test] functions
/// that are not able to be run by the test harness because they are in a
/// position where they are not nameable.
///
/// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
///
/// ### Example
///
/// ```rust,test
/// fn main() {
/// #[test]
/// fn foo() {
/// // This test will not fail because it does not run.
/// assert_eq!(1, 2);
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In order for the test harness to run a test, the test function must be
/// located in a position where it can be accessed from the crate root.
/// This generally means it must be defined in a module, and not anywhere
/// else such as inside another function. The compiler previously allowed
/// this without an error, so a lint was added as an alert that a test is
/// not being used. Whether or not this should be allowed has not yet been
/// decided, see [RFC 2471] and [issue #36629].
///
/// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
/// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
pub UNNAMEABLE_TEST_ITEMS,
Warn,
"detects an item that cannot be named being marked as `#[test_case]`",
report_in_external_macro
}
declare_lint! {
/// The `useless_deprecated` lint detects deprecation attributes with no effect.
///
/// ### Example
///
/// ```rust,compile_fail
/// struct X;
///
/// #[deprecated = "message"]
/// impl Default for X {
/// fn default() -> Self {
/// X
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Deprecation attributes have no effect on trait implementations.
pub USELESS_DEPRECATED,
Deny,
"detects deprecation attributes with no effect",
}
declare_lint! {
/// The `ineffective_unstable_trait_impl` lint detects `#[unstable]` attributes which are not used.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![feature(staged_api)]
///
/// #[derive(Clone)]
/// #[stable(feature = "x", since = "1")]
/// struct S {}
///
/// #[unstable(feature = "y", issue = "none")]
/// impl Copy for S {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// `staged_api` does not currently support using a stability attribute on `impl` blocks.
/// `impl`s are always stable if both the type and trait are stable, and always unstable otherwise.
pub INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
Deny,
"detects `#[unstable]` on stable trait implementations for stable types"
}
declare_lint! {
/// The `self_constructor_from_outer_item` lint detects cases where the `Self` constructor
/// was silently allowed due to a bug in the resolver, and which may produce surprising
/// and unintended behavior.
///
/// Using a `Self` type alias from an outer item was never intended, but was silently allowed.
/// This is deprecated -- and is a hard error when the `Self` type alias references generics
/// that are not in scope.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(self_constructor_from_outer_item)]
///
/// struct S0(usize);
///
/// impl S0 {
/// fn foo() {
/// const C: S0 = Self(0);
/// fn bar() -> S0 {
/// Self(0)
/// }
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The `Self` type alias should not be reachable because nested items are not associated with
/// the scope of the parameters from the parent item.
pub SELF_CONSTRUCTOR_FROM_OUTER_ITEM,
Warn,
"detect unsupported use of `Self` from outer item",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #124186 <https://github.com/rust-lang/rust/issues/124186>",
};
}
declare_lint! {
/// The `semicolon_in_expressions_from_macros` lint detects trailing semicolons
/// in macro bodies when the macro is invoked in expression position.
/// This was previous accepted, but is being phased out.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(semicolon_in_expressions_from_macros)]
/// macro_rules! foo {
/// () => { true; }
/// }
///
/// fn main() {
/// let val = match true {
/// true => false,
/// _ => foo!()
/// };
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous, Rust ignored trailing semicolon in a macro
/// body when a macro was invoked in expression position.
/// However, this makes the treatment of semicolons in the language
/// inconsistent, and could lead to unexpected runtime behavior
/// in some circumstances (e.g. if the macro author expects
/// a value to be dropped).
///
/// This is a [future-incompatible] lint to transition this
/// to a hard error in the future. See [issue #79813] for more details.
///
/// [issue #79813]: https://github.com/rust-lang/rust/issues/79813
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
Deny,
"trailing semicolon in macro body used as expression",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #79813 <https://github.com/rust-lang/rust/issues/79813>",
report_in_deps: true,
};
}
declare_lint! {
/// The `legacy_derive_helpers` lint detects derive helper attributes
/// that are used before they are introduced.
///
/// ### Example
///
/// ```rust,ignore (needs extern crate)
/// #[serde(rename_all = "camelCase")]
/// #[derive(Deserialize)]
/// struct S { /* fields */ }
/// ```
///
/// produces:
///
/// ```text
/// warning: derive helper attribute is used before it is introduced
/// --> $DIR/legacy-derive-helpers.rs:1:3
/// |
/// 1 | #[serde(rename_all = "camelCase")]
/// | ^^^^^
/// ...
/// 2 | #[derive(Deserialize)]
/// | ----------- the attribute is introduced here
/// ```
///
/// ### Explanation
///
/// Attributes like this work for historical reasons, but attribute expansion works in
/// left-to-right order in general, so, to resolve `#[serde]`, compiler has to try to "look
/// into the future" at not yet expanded part of the item , but such attempts are not always
/// reliable.
///
/// To fix the warning place the helper attribute after its corresponding derive.
/// ```rust,ignore (needs extern crate)
/// #[derive(Deserialize)]
/// #[serde(rename_all = "camelCase")]
/// struct S { /* fields */ }
/// ```
pub LEGACY_DERIVE_HELPERS,
Deny,
"detects derive helper attributes that are used before they are introduced",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #79202 <https://github.com/rust-lang/rust/issues/79202>",
report_in_deps: true,
};
}
declare_lint! {
/// The `large_assignments` lint detects when objects of large
/// types are being moved around.
///
/// ### Example
///
/// ```rust,ignore (can crash on some platforms)
/// let x = [0; 50000];
/// let y = x;
/// ```
///
/// produces:
///
/// ```text
/// warning: moving a large value
/// --> $DIR/move-large.rs:1:3
/// let y = x;
/// - Copied large value here
/// ```
///
/// ### Explanation
///
/// When using a large type in a plain assignment or in a function
/// argument, idiomatic code can be inefficient.
/// Ideally appropriate optimizations would resolve this, but such
/// optimizations are only done in a best-effort manner.
/// This lint will trigger on all sites of large moves and thus allow the
/// user to resolve them in code.
pub LARGE_ASSIGNMENTS,
Warn,
"detects large moves or copies",
}
declare_lint! {
/// The `unexpected_cfgs` lint detects unexpected conditional compilation conditions.
///
/// ### Example
///
/// ```text
/// rustc --check-cfg 'cfg()'
/// ```
///
/// ```rust,ignore (needs command line option)
/// #[cfg(widnows)]
/// fn foo() {}
/// ```
///
/// This will produce:
///
/// ```text
/// warning: unexpected `cfg` condition name: `widnows`
/// --> lint_example.rs:1:7
/// |
/// 1 | #[cfg(widnows)]
/// | ^^^^^^^
/// |
/// = note: `#[warn(unexpected_cfgs)]` on by default
/// ```
///
/// ### Explanation
///
/// This lint is only active when [`--check-cfg`][check-cfg] arguments are being
/// passed to the compiler and triggers whenever an unexpected condition name or value is
/// used.
///
/// See the [Checking Conditional Configurations][check-cfg] section for more
/// details.
///
/// See the [Cargo Specifics][unexpected_cfgs_lint_config] section for configuring this lint in
/// `Cargo.toml`.
///
/// [check-cfg]: https://doc.rust-lang.org/nightly/rustc/check-cfg.html
/// [unexpected_cfgs_lint_config]: https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html#check-cfg-in-lintsrust-table
pub UNEXPECTED_CFGS,
Warn,
"detects unexpected names and values in `#[cfg]` conditions",
report_in_external_macro
}
declare_lint! {
/// The `explicit_builtin_cfgs_in_flags` lint detects builtin cfgs set via the `--cfg` flag.
///
/// ### Example
///
/// ```text
/// rustc --cfg unix
/// ```
///
/// ```rust,ignore (needs command line option)
/// fn main() {}
/// ```
///
/// This will produce:
///
/// ```text
/// error: unexpected `--cfg unix` flag
/// |
/// = note: config `unix` is only supposed to be controlled by `--target`
/// = note: manually setting a built-in cfg can and does create incoherent behaviors
/// = note: `#[deny(explicit_builtin_cfgs_in_flags)]` on by default
/// ```
///
/// ### Explanation
///
/// Setting builtin cfgs can and does produce incoherent behavior, it's better to the use
/// the appropriate `rustc` flag that controls the config. For example setting the `windows`
/// cfg but on Linux based target.
pub EXPLICIT_BUILTIN_CFGS_IN_FLAGS,
Deny,
"detects builtin cfgs set via the `--cfg`"
}
declare_lint! {
/// The `repr_transparent_external_private_fields` lint
/// detects types marked `#[repr(transparent)]` that (transitively)
/// contain an external ZST type marked `#[non_exhaustive]` or containing
/// private fields
///
/// ### Example
///
/// ```rust,ignore (needs external crate)
/// #![deny(repr_transparent_external_private_fields)]
/// use foo::NonExhaustiveZst;
///
/// #[repr(transparent)]
/// struct Bar(u32, ([u32; 0], NonExhaustiveZst));
/// ```
///
/// This will produce:
///
/// ```text
/// error: zero-sized fields in repr(transparent) cannot contain external non-exhaustive types
/// --> src/main.rs:5:28
/// |
/// 5 | struct Bar(u32, ([u32; 0], NonExhaustiveZst));
/// | ^^^^^^^^^^^^^^^^
/// |
/// note: the lint level is defined here
/// --> src/main.rs:1:9
/// |
/// 1 | #![deny(repr_transparent_external_private_fields)]
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #78586 <https://github.com/rust-lang/rust/issues/78586>
/// = note: this struct contains `NonExhaustiveZst`, which is marked with `#[non_exhaustive]`, and makes it not a breaking change to become non-zero-sized in the future.
/// ```
///
/// ### Explanation
///
/// Previous, Rust accepted fields that contain external private zero-sized types,
/// even though it should not be a breaking change to add a non-zero-sized field to
/// that private type.
///
/// This is a [future-incompatible] lint to transition this
/// to a hard error in the future. See [issue #78586] for more details.
///
/// [issue #78586]: https://github.com/rust-lang/rust/issues/78586
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS,
Warn,
"transparent type contains an external ZST that is marked #[non_exhaustive] or contains private fields",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #78586 <https://github.com/rust-lang/rust/issues/78586>",
};
}
declare_lint! {
/// The `unstable_syntax_pre_expansion` lint detects the use of unstable
/// syntax that is discarded during attribute expansion.
///
/// ### Example
///
/// ```rust
/// #[cfg(FALSE)]
/// macro foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The input to active attributes such as `#[cfg]` or procedural macro
/// attributes is required to be valid syntax. Previously, the compiler only
/// gated the use of unstable syntax features after resolving `#[cfg]` gates
/// and expanding procedural macros.
///
/// To avoid relying on unstable syntax, move the use of unstable syntax
/// into a position where the compiler does not parse the syntax, such as a
/// functionlike macro.
///
/// ```rust
/// # #![deny(unstable_syntax_pre_expansion)]
///
/// macro_rules! identity {
/// ( $($tokens:tt)* ) => { $($tokens)* }
/// }
///
/// #[cfg(FALSE)]
/// identity! {
/// macro foo() {}
/// }
/// ```
///
/// This is a [future-incompatible] lint to transition this
/// to a hard error in the future. See [issue #65860] for more details.
///
/// [issue #65860]: https://github.com/rust-lang/rust/issues/65860
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub UNSTABLE_SYNTAX_PRE_EXPANSION,
Warn,
"unstable syntax can change at any point in the future, causing a hard error!",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #65860 <https://github.com/rust-lang/rust/issues/65860>",
};
}
declare_lint! {
/// The `ambiguous_glob_reexports` lint detects cases where names re-exported via globs
/// collide. Downstream users trying to use the same name re-exported from multiple globs
/// will receive a warning pointing out redefinition of the same name.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(ambiguous_glob_reexports)]
/// pub mod foo {
/// pub type X = u8;
/// }
///
/// pub mod bar {
/// pub type Y = u8;
/// pub type X = u8;
/// }
///
/// pub use foo::*;
/// pub use bar::*;
///
///
/// pub fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This was previously accepted but it could silently break a crate's downstream users code.
/// For example, if `foo::*` and `bar::*` were re-exported before `bar::X` was added to the
/// re-exports, down stream users could use `this_crate::X` without problems. However, adding
/// `bar::X` would cause compilation errors in downstream crates because `X` is defined
/// multiple times in the same namespace of `this_crate`.
pub AMBIGUOUS_GLOB_REEXPORTS,
Warn,
"ambiguous glob re-exports",
}
declare_lint! {
/// The `hidden_glob_reexports` lint detects cases where glob re-export items are shadowed by
/// private items.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(hidden_glob_reexports)]
///
/// pub mod upstream {
/// mod inner { pub struct Foo {}; pub struct Bar {}; }
/// pub use self::inner::*;
/// struct Foo {} // private item shadows `inner::Foo`
/// }
///
/// // mod downstream {
/// // fn test() {
/// // let _ = crate::upstream::Foo; // inaccessible
/// // }
/// // }
///
/// pub fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This was previously accepted without any errors or warnings but it could silently break a
/// crate's downstream user code. If the `struct Foo` was added, `dep::inner::Foo` would
/// silently become inaccessible and trigger a "`struct `Foo` is private`" visibility error at
/// the downstream use site.
pub HIDDEN_GLOB_REEXPORTS,
Warn,
"name introduced by a private item shadows a name introduced by a public glob re-export",
}
declare_lint! {
/// The `long_running_const_eval` lint is emitted when const
/// eval is running for a long time to ensure rustc terminates
/// even if you accidentally wrote an infinite loop.
///
/// ### Example
///
/// ```rust,compile_fail
/// const FOO: () = loop {};
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Loops allow const evaluation to compute arbitrary code, but may also
/// cause infinite loops or just very long running computations.
/// Users can enable long running computations by allowing the lint
/// on individual constants or for entire crates.
///
/// ### Unconditional warnings
///
/// Note that regardless of whether the lint is allowed or set to warn,
/// the compiler will issue warnings if constant evaluation runs significantly
/// longer than this lint's limit. These warnings are also shown to downstream
/// users from crates.io or similar registries. If you are above the lint's limit,
/// both you and downstream users might be exposed to these warnings.
/// They might also appear on compiler updates, as the compiler makes minor changes
/// about how complexity is measured: staying below the limit ensures that there
/// is enough room, and given that the lint is disabled for people who use your
/// dependency it means you will be the only one to get the warning and can put
/// out an update in your own time.
pub LONG_RUNNING_CONST_EVAL,
Deny,
"detects long const eval operations",
report_in_external_macro
}
declare_lint! {
/// The `unused_associated_type_bounds` lint is emitted when an
/// associated type bound is added to a trait object, but the associated
/// type has a `where Self: Sized` bound, and is thus unavailable on the
/// trait object anyway.
///
/// ### Example
///
/// ```rust
/// trait Foo {
/// type Bar where Self: Sized;
/// }
/// type Mop = dyn Foo<Bar = ()>;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Just like methods with `Self: Sized` bounds are unavailable on trait
/// objects, associated types can be removed from the trait object.
pub UNUSED_ASSOCIATED_TYPE_BOUNDS,
Warn,
"detects unused `Foo = Bar` bounds in `dyn Trait<Foo = Bar>`"
}
declare_lint! {
/// The `unused_doc_comments` lint detects doc comments that aren't used
/// by `rustdoc`.
///
/// ### Example
///
/// ```rust
/// /// docs for x
/// let x = 12;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// `rustdoc` does not use doc comments in all positions, and so the doc
/// comment will be ignored. Try changing it to a normal comment with `//`
/// to avoid the warning.
pub UNUSED_DOC_COMMENTS,
Warn,
"detects doc comments that aren't used by rustdoc"
}
declare_lint! {
/// The `rust_2021_incompatible_closure_captures` lint detects variables that aren't completely
/// captured in Rust 2021, such that the `Drop` order of their fields may differ between
/// Rust 2018 and 2021.
///
/// It can also detect when a variable implements a trait like `Send`, but one of its fields does not,
/// and the field is captured by a closure and used with the assumption that said field implements
/// the same trait as the root variable.
///
/// ### Example of drop reorder
///
/// ```rust,edition2018,compile_fail
/// #![deny(rust_2021_incompatible_closure_captures)]
/// # #![allow(unused)]
///
/// struct FancyInteger(i32);
///
/// impl Drop for FancyInteger {
/// fn drop(&mut self) {
/// println!("Just dropped {}", self.0);
/// }
/// }
///
/// struct Point { x: FancyInteger, y: FancyInteger }
///
/// fn main() {
/// let p = Point { x: FancyInteger(10), y: FancyInteger(20) };
///
/// let c = || {
/// let x = p.x;
/// };
///
/// c();
///
/// // ... More code ...
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In the above example, `p.y` will be dropped at the end of `f` instead of
/// with `c` in Rust 2021.
///
/// ### Example of auto-trait
///
/// ```rust,edition2018,compile_fail
/// #![deny(rust_2021_incompatible_closure_captures)]
/// use std::thread;
///
/// struct Pointer(*mut i32);
/// unsafe impl Send for Pointer {}
///
/// fn main() {
/// let mut f = 10;
/// let fptr = Pointer(&mut f as *mut i32);
/// thread::spawn(move || unsafe {
/// *fptr.0 = 20;
/// });
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In the above example, only `fptr.0` is captured in Rust 2021.
/// The field is of type `*mut i32`, which doesn't implement `Send`,
/// making the code invalid as the field cannot be sent between threads safely.
pub RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
Allow,
"detects closures affected by Rust 2021 changes",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2021),
explain_reason: false,
};
}
declare_lint_pass!(UnusedDocComment => [UNUSED_DOC_COMMENTS]);
declare_lint! {
/// The `missing_abi` lint detects cases where the ABI is omitted from
/// `extern` declarations.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(missing_abi)]
///
/// extern fn foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// For historic reasons, Rust implicitly selects `C` as the default ABI for
/// `extern` declarations. [Other ABIs] like `C-unwind` and `system` have
/// been added since then, and especially with their addition seeing the ABI
/// easily makes code review easier.
///
/// [Other ABIs]: https://doc.rust-lang.org/reference/items/external-blocks.html#abi
pub MISSING_ABI,
Warn,
"No declared ABI for extern declaration"
}
declare_lint! {
/// The `invalid_doc_attributes` lint detects when the `#[doc(...)]` is
/// misused.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(warnings)]
///
/// pub mod submodule {
/// #![doc(test(no_crate_inject))]
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previously, incorrect usage of the `#[doc(..)]` attribute was not
/// being validated. Usually these should be rejected as a hard error,
/// but this lint was introduced to avoid breaking any existing
/// crates which included them.
pub INVALID_DOC_ATTRIBUTES,
Deny,
"detects invalid `#[doc(...)]` attributes",
}
declare_lint! {
/// The `rust_2021_incompatible_or_patterns` lint detects usage of old versions of or-patterns.
///
/// ### Example
///
/// ```rust,edition2018,compile_fail
/// #![deny(rust_2021_incompatible_or_patterns)]
///
/// macro_rules! match_any {
/// ( $expr:expr , $( $( $pat:pat )|+ => $expr_arm:expr ),+ ) => {
/// match $expr {
/// $(
/// $( $pat => $expr_arm, )+
/// )+
/// }
/// };
/// }
///
/// fn main() {
/// let result: Result<i64, i32> = Err(42);
/// let int: i64 = match_any!(result, Ok(i) | Err(i) => i.into());
/// assert_eq!(int, 42);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In Rust 2021, the `pat` matcher will match additional patterns, which include the `|` character.
pub RUST_2021_INCOMPATIBLE_OR_PATTERNS,
Allow,
"detects usage of old versions of or-patterns",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2021/or-patterns-macro-rules.html>",
};
}
declare_lint! {
/// The `rust_2021_prelude_collisions` lint detects the usage of trait methods which are ambiguous
/// with traits added to the prelude in future editions.
///
/// ### Example
///
/// ```rust,edition2018,compile_fail
/// #![deny(rust_2021_prelude_collisions)]
///
/// trait Foo {
/// fn try_into(self) -> Result<String, !>;
/// }
///
/// impl Foo for &str {
/// fn try_into(self) -> Result<String, !> {
/// Ok(String::from(self))
/// }
/// }
///
/// fn main() {
/// let x: String = "3".try_into().unwrap();
/// // ^^^^^^^^
/// // This call to try_into matches both Foo::try_into and TryInto::try_into as
/// // `TryInto` has been added to the Rust prelude in 2021 edition.
/// println!("{x}");
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In Rust 2021, one of the important introductions is the [prelude changes], which add
/// `TryFrom`, `TryInto`, and `FromIterator` into the standard library's prelude. Since this
/// results in an ambiguity as to which method/function to call when an existing `try_into`
/// method is called via dot-call syntax or a `try_from`/`from_iter` associated function
/// is called directly on a type.
///
/// [prelude changes]: https://blog.rust-lang.org/inside-rust/2021/03/04/planning-rust-2021.html#prelude-changes
pub RUST_2021_PRELUDE_COLLISIONS,
Allow,
"detects the usage of trait methods which are ambiguous with traits added to the \
prelude in future editions",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2021/prelude.html>",
};
}
declare_lint! {
/// The `rust_2024_prelude_collisions` lint detects the usage of trait methods which are ambiguous
/// with traits added to the prelude in future editions.
///
/// ### Example
///
/// ```rust,edition2021,compile_fail
/// #![deny(rust_2024_prelude_collisions)]
/// trait Meow {
/// fn poll(&self) {}
/// }
/// impl<T> Meow for T {}
///
/// fn main() {
/// core::pin::pin!(async {}).poll();
/// // ^^^^^^
/// // This call to try_into matches both Future::poll and Meow::poll as
/// // `Future` has been added to the Rust prelude in 2024 edition.
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Rust 2024, introduces two new additions to the standard library's prelude:
/// `Future` and `IntoFuture`. This results in an ambiguity as to which method/function
/// to call when an existing `poll`/`into_future` method is called via dot-call syntax or
/// a `poll`/`into_future` associated function is called directly on a type.
///
pub RUST_2024_PRELUDE_COLLISIONS,
Allow,
"detects the usage of trait methods which are ambiguous with traits added to the \
prelude in future editions",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2024),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2024/prelude.html>",
};
}
declare_lint! {
/// The `rust_2021_prefixes_incompatible_syntax` lint detects identifiers that will be parsed as a
/// prefix instead in Rust 2021.
///
/// ### Example
///
/// ```rust,edition2018,compile_fail
/// #![deny(rust_2021_prefixes_incompatible_syntax)]
///
/// macro_rules! m {
/// (z $x:expr) => ();
/// }
///
/// m!(z"hey");
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In Rust 2015 and 2018, `z"hey"` is two tokens: the identifier `z`
/// followed by the string literal `"hey"`. In Rust 2021, the `z` is
/// considered a prefix for `"hey"`.
///
/// This lint suggests to add whitespace between the `z` and `"hey"` tokens
/// to keep them separated in Rust 2021.
// Allow this lint -- rustdoc doesn't yet support threading edition into this lint's parser.
#[allow(rustdoc::invalid_rust_codeblocks)]
pub RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
Allow,
"identifiers that will be parsed as a prefix in Rust 2021",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2021/reserving-syntax.html>",
};
crate_level_only
}
declare_lint! {
/// The `unsupported_calling_conventions` lint is output whenever there is a use of the
/// `stdcall`, `fastcall`, and `cdecl` calling conventions (or their unwind
/// variants) on targets that cannot meaningfully be supported for the requested target.
///
/// For example `stdcall` does not make much sense for a x86_64 or, more apparently, powerpc
/// code, because this calling convention was never specified for those targets.
///
/// Historically MSVC toolchains have fallen back to the regular C calling convention for
/// targets other than x86, but Rust doesn't really see a similar need to introduce a similar
/// hack across many more targets.
///
/// ### Example
///
/// ```rust,ignore (needs specific targets)
/// extern "stdcall" fn stdcall() {}
/// ```
///
/// This will produce:
///
/// ```text
/// warning: use of calling convention not supported on this target
/// --> $DIR/unsupported.rs:39:1
/// |
/// LL | extern "stdcall" fn stdcall() {}
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// |
/// = note: `#[warn(unsupported_calling_conventions)]` on by default
/// = warning: this was previously accepted by the compiler but is being phased out;
/// it will become a hard error in a future release!
/// = note: for more information, see issue ...
/// ```
///
/// ### Explanation
///
/// On most of the targets the behaviour of `stdcall` and similar calling conventions is not
/// defined at all, but was previously accepted due to a bug in the implementation of the
/// compiler.
pub UNSUPPORTED_CALLING_CONVENTIONS,
Warn,
"use of unsupported calling convention",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
report_in_deps: false,
reference: "issue #137018 <https://github.com/rust-lang/rust/issues/137018>",
};
}
declare_lint! {
/// The `unsupported_fn_ptr_calling_conventions` lint is output whenever there is a use of
/// a target dependent calling convention on a target that does not support this calling
/// convention on a function pointer.
///
/// For example `stdcall` does not make much sense for a x86_64 or, more apparently, powerpc
/// code, because this calling convention was never specified for those targets.
///
/// ### Example
///
/// ```rust,ignore (needs specific targets)
/// fn stdcall_ptr(f: extern "stdcall" fn ()) {
/// f()
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// warning: the calling convention `"stdcall"` is not supported on this target
/// --> $DIR/unsupported.rs:34:15
/// |
/// LL | fn stdcall_ptr(f: extern "stdcall" fn()) {
/// | ^^^^^^^^^^^^^^^^^^^^^^^^
/// |
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #130260 <https://github.com/rust-lang/rust/issues/130260>
/// = note: `#[warn(unsupported_fn_ptr_calling_conventions)]` on by default
/// ```
///
/// ### Explanation
///
/// On most of the targets the behaviour of `stdcall` and similar calling conventions is not
/// defined at all, but was previously accepted due to a bug in the implementation of the
/// compiler.
pub UNSUPPORTED_FN_PTR_CALLING_CONVENTIONS,
Warn,
"use of unsupported calling convention for function pointer",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #130260 <https://github.com/rust-lang/rust/issues/130260>",
report_in_deps: true,
};
}
declare_lint! {
/// The `break_with_label_and_loop` lint detects labeled `break` expressions with
/// an unlabeled loop as their value expression.
///
/// ### Example
///
/// ```rust
/// 'label: loop {
/// break 'label loop { break 42; };
/// };
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In Rust, loops can have a label, and `break` expressions can refer to that label to
/// break out of specific loops (and not necessarily the innermost one). `break` expressions
/// can also carry a value expression, which can be another loop. A labeled `break` with an
/// unlabeled loop as its value expression is easy to confuse with an unlabeled break with
/// a labeled loop and is thus discouraged (but allowed for compatibility); use parentheses
/// around the loop expression to silence this warning. Unlabeled `break` expressions with
/// labeled loops yield a hard error, which can also be silenced by wrapping the expression
/// in parentheses.
pub BREAK_WITH_LABEL_AND_LOOP,
Warn,
"`break` expression with label and unlabeled loop as value expression"
}
declare_lint! {
/// The `non_exhaustive_omitted_patterns` lint aims to help consumers of a `#[non_exhaustive]`
/// struct or enum who want to match all of its fields/variants explicitly.
///
/// The `#[non_exhaustive]` annotation forces matches to use wildcards, so exhaustiveness
/// checking cannot be used to ensure that all fields/variants are matched explicitly. To remedy
/// this, this allow-by-default lint warns the user when a match mentions some but not all of
/// the fields/variants of a `#[non_exhaustive]` struct or enum.
///
/// ### Example
///
/// ```rust,ignore (needs separate crate)
/// // crate A
/// #[non_exhaustive]
/// pub enum Bar {
/// A,
/// B, // added variant in non breaking change
/// }
///
/// // in crate B
/// #![feature(non_exhaustive_omitted_patterns_lint)]
/// #[warn(non_exhaustive_omitted_patterns)]
/// match Bar::A {
/// Bar::A => {},
/// _ => {},
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// warning: some variants are not matched explicitly
/// --> $DIR/reachable-patterns.rs:70:9
/// |
/// LL | match Bar::A {
/// | ^ pattern `Bar::B` not covered
/// |
/// note: the lint level is defined here
/// --> $DIR/reachable-patterns.rs:69:16
/// |
/// LL | #[warn(non_exhaustive_omitted_patterns)]
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// = help: ensure that all variants are matched explicitly by adding the suggested match arms
/// = note: the matched value is of type `Bar` and the `non_exhaustive_omitted_patterns` attribute was found
/// ```
///
/// Warning: setting this to `deny` will make upstream non-breaking changes (adding fields or
/// variants to a `#[non_exhaustive]` struct or enum) break your crate. This goes against
/// expected semver behavior.
///
/// ### Explanation
///
/// Structs and enums tagged with `#[non_exhaustive]` force the user to add a (potentially
/// redundant) wildcard when pattern-matching, to allow for future addition of fields or
/// variants. The `non_exhaustive_omitted_patterns` lint detects when such a wildcard happens to
/// actually catch some fields/variants. In other words, when the match without the wildcard
/// would not be exhaustive. This lets the user be informed if new fields/variants were added.
pub NON_EXHAUSTIVE_OMITTED_PATTERNS,
Allow,
"detect when patterns of types marked `non_exhaustive` are missed",
@feature_gate = non_exhaustive_omitted_patterns_lint;
}
declare_lint! {
/// The `text_direction_codepoint_in_comment` lint detects Unicode codepoints in comments that
/// change the visual representation of text on screen in a way that does not correspond to
/// their on memory representation.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(text_direction_codepoint_in_comment)]
/// fn main() {
#[doc = " println!(\"{:?}\"); // '\u{202E}');"]
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unicode allows changing the visual flow of text on screen in order to support scripts that
/// are written right-to-left, but a specially crafted comment can make code that will be
/// compiled appear to be part of a comment, depending on the software used to read the code.
/// To avoid potential problems or confusion, such as in CVE-2021-42574, by default we deny
/// their use.
pub TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
Deny,
"invisible directionality-changing codepoints in comment",
crate_level_only
}
declare_lint! {
/// The `text_direction_codepoint_in_literal` lint detects Unicode codepoints that change the
/// visual representation of text on screen in a way that does not correspond to their on
/// memory representation.
///
/// ### Explanation
///
/// The unicode characters `\u{202A}`, `\u{202B}`, `\u{202D}`, `\u{202E}`, `\u{2066}`,
/// `\u{2067}`, `\u{2068}`, `\u{202C}` and `\u{2069}` make the flow of text on screen change
/// its direction on software that supports these codepoints. This makes the text "abc" display
/// as "cba" on screen. By leveraging software that supports these, people can write specially
/// crafted literals that make the surrounding code seem like it's performing one action, when
/// in reality it is performing another. Because of this, we proactively lint against their
/// presence to avoid surprises.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(text_direction_codepoint_in_literal)]
/// fn main() {
// ` - convince tidy that backticks match
#[doc = " println!(\"{:?}\", '\u{202E}');"]
// `
/// }
/// ```
///
/// {{produces}}
///
pub TEXT_DIRECTION_CODEPOINT_IN_LITERAL,
Deny,
"detect special Unicode codepoints that affect the visual representation of text on screen, \
changing the direction in which text flows",
crate_level_only
}
declare_lint! {
/// The `duplicate_macro_attributes` lint detects when a `#[test]`-like built-in macro
/// attribute is duplicated on an item. This lint may trigger on `bench`, `cfg_eval`, `test`
/// and `test_case`.
///
/// ### Example
///
/// ```rust,ignore (needs --test)
/// #[test]
/// #[test]
/// fn foo() {}
/// ```
///
/// This will produce:
///
/// ```text
/// warning: duplicated attribute
/// --> src/lib.rs:2:1
/// |
/// 2 | #[test]
/// | ^^^^^^^
/// |
/// = note: `#[warn(duplicate_macro_attributes)]` on by default
/// ```
///
/// ### Explanation
///
/// A duplicated attribute may erroneously originate from a copy-paste and the effect of it
/// being duplicated may not be obvious or desirable.
///
/// For instance, doubling the `#[test]` attributes registers the test to be run twice with no
/// change to its environment.
///
/// [issue #90979]: https://github.com/rust-lang/rust/issues/90979
pub DUPLICATE_MACRO_ATTRIBUTES,
Warn,
"duplicated attribute"
}
declare_lint! {
/// The `deprecated_where_clause_location` lint detects when a where clause in front of the equals
/// in an associated type.
///
/// ### Example
///
/// ```rust
/// trait Trait {
/// type Assoc<'a> where Self: 'a;
/// }
///
/// impl Trait for () {
/// type Assoc<'a> where Self: 'a = ();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The preferred location for where clauses on associated types
/// is after the type. However, for most of generic associated types development,
/// it was only accepted before the equals. To provide a transition period and
/// further evaluate this change, both are currently accepted. At some point in
/// the future, this may be disallowed at an edition boundary; but, that is
/// undecided currently.
pub DEPRECATED_WHERE_CLAUSE_LOCATION,
Warn,
"deprecated where clause location"
}
declare_lint! {
/// The `test_unstable_lint` lint tests unstable lints and is perma-unstable.
///
/// ### Example
///
/// ```rust
/// // This lint is intentionally used to test the compiler's behavior
/// // when an unstable lint is enabled without the corresponding feature gate.
/// #![allow(test_unstable_lint)]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In order to test the behavior of unstable lints, a permanently-unstable
/// lint is required. This lint can be used to trigger warnings and errors
/// from the compiler related to unstable lints.
pub TEST_UNSTABLE_LINT,
Deny,
"this unstable lint is only for testing",
@feature_gate = test_unstable_lint;
}
declare_lint! {
/// The `ffi_unwind_calls` lint detects calls to foreign functions or function pointers with
/// `C-unwind` or other FFI-unwind ABIs.
///
/// ### Example
///
/// ```rust
/// #![warn(ffi_unwind_calls)]
///
/// unsafe extern "C-unwind" {
/// fn foo();
/// }
///
/// fn bar() {
/// unsafe { foo(); }
/// let ptr: unsafe extern "C-unwind" fn() = foo;
/// unsafe { ptr(); }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// For crates containing such calls, if they are compiled with `-C panic=unwind` then the
/// produced library cannot be linked with crates compiled with `-C panic=abort`. For crates
/// that desire this ability it is therefore necessary to avoid such calls.
pub FFI_UNWIND_CALLS,
Allow,
"call to foreign functions or function pointers with FFI-unwind ABI"
}
declare_lint! {
/// The `linker_messages` lint forwards warnings from the linker.
///
/// ### Example
///
/// ```rust,ignore (needs CLI args, platform-specific)
/// #[warn(linker_messages)]
/// extern "C" {
/// fn foo();
/// }
/// fn main () { unsafe { foo(); } }
/// ```
///
/// On Linux, using `gcc -Wl,--warn-unresolved-symbols` as a linker, this will produce
///
/// ```text
/// warning: linker stderr: rust-lld: undefined symbol: foo
/// >>> referenced by rust_out.69edbd30df4ae57d-cgu.0
/// >>> rust_out.rust_out.69edbd30df4ae57d-cgu.0.rcgu.o:(rust_out::main::h3a90094b06757803)
/// |
/// note: the lint level is defined here
/// --> warn.rs:1:9
/// |
/// 1 | #![warn(linker_messages)]
/// | ^^^^^^^^^^^^^^^
/// warning: 1 warning emitted
/// ```
///
/// ### Explanation
///
/// Linkers emit platform-specific and program-specific warnings that cannot be predicted in
/// advance by the Rust compiler. Such messages are ignored by default for now. While linker
/// warnings could be very useful they have been ignored for many years by essentially all
/// users, so we need to do a bit more work than just surfacing their text to produce a clear
/// and actionable warning of similar quality to our other diagnostics. See this tracking
/// issue for more details: <https://github.com/rust-lang/rust/issues/136096>.
pub LINKER_MESSAGES,
Allow,
"warnings emitted at runtime by the target-specific linker program"
}
declare_lint! {
/// The `named_arguments_used_positionally` lint detects cases where named arguments are only
/// used positionally in format strings. This usage is valid but potentially very confusing.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(named_arguments_used_positionally)]
/// fn main() {
/// let _x = 5;
/// println!("{}", _x = 1); // Prints 1, will trigger lint
///
/// println!("{}", _x); // Prints 5, no lint emitted
/// println!("{_x}", _x = _x); // Prints 5, no lint emitted
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Rust formatting strings can refer to named arguments by their position, but this usage is
/// potentially confusing. In particular, readers can incorrectly assume that the declaration
/// of named arguments is an assignment (which would produce the unit type).
/// For backwards compatibility, this is not a hard error.
pub NAMED_ARGUMENTS_USED_POSITIONALLY,
Warn,
"named arguments in format used positionally"
}
declare_lint! {
/// The `never_type_fallback_flowing_into_unsafe` lint detects cases where never type fallback
/// affects unsafe function calls.
///
/// ### Never type fallback
///
/// When the compiler sees a value of type [`!`] it implicitly inserts a coercion (if possible),
/// to allow type check to infer any type:
///
/// ```ignore (illustrative-and-has-placeholders)
/// // this
/// let x: u8 = panic!();
///
/// // is (essentially) turned by the compiler into
/// let x: u8 = absurd(panic!());
///
/// // where absurd is a function with the following signature
/// // (it's sound, because `!` always marks unreachable code):
/// fn absurd<T>(never: !) -> T { ... }
/// ```
///
/// While it's convenient to be able to use non-diverging code in one of the branches (like
/// `if a { b } else { return }`) this could lead to compilation errors:
///
/// ```compile_fail
/// // this
/// { panic!() };
///
/// // gets turned into this
/// { absurd(panic!()) }; // error: can't infer the type of `absurd`
/// ```
///
/// To prevent such errors, compiler remembers where it inserted `absurd` calls, and if it
/// can't infer their type, it sets the type to fallback. `{ absurd::<Fallback>(panic!()) };`.
/// This is what is known as "never type fallback".
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(never_type_fallback_flowing_into_unsafe)]
/// fn main() {
/// if true {
/// // return has type `!` which, is some cases, causes never type fallback
/// return
/// } else {
/// // `zeroed` is an unsafe function, which returns an unbounded type
/// unsafe { std::mem::zeroed() }
/// };
/// // depending on the fallback, `zeroed` may create `()` (which is completely sound),
/// // or `!` (which is instant undefined behavior)
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Due to historic reasons never type fallback was `()`, meaning that `!` got spontaneously
/// coerced to `()`. There are plans to change that, but they may make the code such as above
/// unsound. Instead of depending on the fallback, you should specify the type explicitly:
/// ```
/// if true {
/// return
/// } else {
/// // type is explicitly specified, fallback can't hurt us no more
/// unsafe { std::mem::zeroed::<()>() }
/// };
/// ```
///
/// See [Tracking Issue for making `!` fall back to `!`](https://github.com/rust-lang/rust/issues/123748).
///
/// [`!`]: https://doc.rust-lang.org/core/primitive.never.html
/// [`()`]: https://doc.rust-lang.org/core/primitive.unit.html
pub NEVER_TYPE_FALLBACK_FLOWING_INTO_UNSAFE,
Warn,
"never type fallback affecting unsafe function calls",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionAndFutureReleaseSemanticsChange(Edition::Edition2024),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>",
report_in_deps: true,
};
@edition Edition2024 => Deny;
report_in_external_macro
}
declare_lint! {
/// The `dependency_on_unit_never_type_fallback` lint detects cases where code compiles with
/// [never type fallback] being [`()`], but will stop compiling with fallback being [`!`].
///
/// [never type fallback]: https://doc.rust-lang.org/nightly/core/primitive.never.html#never-type-fallback
/// [`!`]: https://doc.rust-lang.org/core/primitive.never.html
/// [`()`]: https://doc.rust-lang.org/core/primitive.unit.html
///
/// ### Example
///
/// ```rust,compile_fail,edition2021
/// #![deny(dependency_on_unit_never_type_fallback)]
/// fn main() {
/// if true {
/// // return has type `!` which, is some cases, causes never type fallback
/// return
/// } else {
/// // the type produced by this call is not specified explicitly,
/// // so it will be inferred from the previous branch
/// Default::default()
/// };
/// // depending on the fallback, this may compile (because `()` implements `Default`),
/// // or it may not (because `!` does not implement `Default`)
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Due to historic reasons never type fallback was `()`, meaning that `!` got spontaneously
/// coerced to `()`. There are plans to change that, but they may make the code such as above
/// not compile. Instead of depending on the fallback, you should specify the type explicitly:
/// ```
/// if true {
/// return
/// } else {
/// // type is explicitly specified, fallback can't hurt us no more
/// <() as Default>::default()
/// };
/// ```
///
/// See [Tracking Issue for making `!` fall back to `!`](https://github.com/rust-lang/rust/issues/123748).
pub DEPENDENCY_ON_UNIT_NEVER_TYPE_FALLBACK,
Warn,
"never type fallback affecting unsafe function calls",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionAndFutureReleaseError(Edition::Edition2024),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html>",
report_in_deps: true,
};
report_in_external_macro
}
declare_lint! {
/// The `invalid_macro_export_arguments` lint detects cases where `#[macro_export]` is being used with invalid arguments.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(invalid_macro_export_arguments)]
///
/// #[macro_export(invalid_parameter)]
/// macro_rules! myMacro {
/// () => {
/// // [...]
/// }
/// }
///
/// #[macro_export(too, many, items)]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The only valid argument is `#[macro_export(local_inner_macros)]` or no argument (`#[macro_export]`).
/// You can't have multiple arguments in a `#[macro_export(..)]`, or mention arguments other than `local_inner_macros`.
///
pub INVALID_MACRO_EXPORT_ARGUMENTS,
Warn,
"\"invalid_parameter\" isn't a valid argument for `#[macro_export]`",
}
declare_lint! {
/// The `private_interfaces` lint detects types in a primary interface of an item,
/// that are more private than the item itself. Primary interface of an item is all
/// its interface except for bounds on generic parameters and where clauses.
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![allow(unused)]
/// #![deny(private_interfaces)]
/// struct SemiPriv;
///
/// mod m1 {
/// struct Priv;
/// impl crate::SemiPriv {
/// pub fn f(_: Priv) {}
/// }
/// }
///
/// # fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Having something private in primary interface guarantees that
/// the item will be unusable from outer modules due to type privacy.
pub PRIVATE_INTERFACES,
Warn,
"private type in primary interface of an item",
}
declare_lint! {
/// The `private_bounds` lint detects types in a secondary interface of an item,
/// that are more private than the item itself. Secondary interface of an item consists of
/// bounds on generic parameters and where clauses, including supertraits for trait items.
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![allow(unused)]
/// #![deny(private_bounds)]
///
/// struct PrivTy;
/// pub struct S
/// where PrivTy:
/// {}
/// # fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Having private types or traits in item bounds makes it less clear what interface
/// the item actually provides.
pub PRIVATE_BOUNDS,
Warn,
"private type in secondary interface of an item",
}
declare_lint! {
/// The `unnameable_types` lint detects types for which you can get objects of that type,
/// but cannot name the type itself.
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![allow(unused)]
/// #![deny(unnameable_types)]
/// mod m {
/// pub struct S;
/// }
///
/// pub fn get_unnameable() -> m::S { m::S }
/// # fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is often expected that if you can obtain an object of type `T`, then
/// you can name the type `T` as well; this lint attempts to enforce this rule.
/// The recommended action is to either reexport the type properly to make it nameable,
/// or document that users are not supposed to be able to name it for one reason or another.
///
/// Besides types, this lint applies to traits because traits can also leak through signatures,
/// and you may obtain objects of their `dyn Trait` or `impl Trait` types.
pub UNNAMEABLE_TYPES,
Allow,
"effective visibility of a type is larger than the area in which it can be named",
}
declare_lint! {
/// The `malformed_diagnostic_attributes` lint detects malformed diagnostic attributes.
///
/// ### Example
///
/// ```rust
/// #[diagnostic::do_not_recommend(message = "message")]
/// trait Trait {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is usually a mistake to use options or syntax that is not supported. Check the spelling,
/// and check the diagnostic attribute listing for the correct name and syntax. Also consider if
/// you are using an old version of the compiler; perhaps the option or syntax is only available
/// in a newer version. See the [reference] for a list of diagnostic attributes and the syntax
/// of each.
///
/// [reference]: https://doc.rust-lang.org/nightly/reference/attributes/diagnostics.html#the-diagnostic-tool-attribute-namespace
pub MALFORMED_DIAGNOSTIC_ATTRIBUTES,
Warn,
"detects malformed diagnostic attributes",
}
declare_lint! {
/// The `misplaced_diagnostic_attributes` lint detects wrongly placed diagnostic attributes.
///
/// ### Example
///
/// ```rust
/// #[diagnostic::do_not_recommend]
/// struct NotUserFacing;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is usually a mistake to specify a diagnostic attribute on an item it is not meant for.
/// For example, `#[diagnostic::do_not_recommend]` can only be placed on trait implementations,
/// and does nothing if placed elsewhere. See the [reference] for a list of diagnostic
/// attributes and their correct positions.
///
/// [reference]: https://doc.rust-lang.org/nightly/reference/attributes/diagnostics.html#the-diagnostic-tool-attribute-namespace
pub MISPLACED_DIAGNOSTIC_ATTRIBUTES,
Warn,
"detects diagnostic attributes that are placed on the wrong item",
}
declare_lint! {
/// The `unknown_diagnostic_attributes` lint detects unknown diagnostic attributes.
///
/// ### Example
///
/// ```rust
/// #[diagnostic::does_not_exist]
/// struct Thing;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is usually a mistake to specify a diagnostic attribute that does not exist. Check the
/// spelling, and check the diagnostic attribute listing for the correct name. Also consider if
/// you are using an old version of the compiler and the attribute is only available in a newer
/// version. See the [reference] for the list of diagnostic attributes.
///
/// [reference]: https://doc.rust-lang.org/nightly/reference/attributes/diagnostics.html#the-diagnostic-tool-attribute-namespace
pub UNKNOWN_DIAGNOSTIC_ATTRIBUTES,
Warn,
"detects unknown diagnostic attributes",
}
declare_lint! {
/// The `malformed_diagnostic_format_literals` lint detects malformed diagnostic format
/// literals.
///
/// ### Example
///
/// ```rust
/// #[diagnostic::on_unimplemented(message = "{Self}} does not implement `Trait`")]
/// trait Trait {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The `#[diagnostic::on_unimplemented]` attribute accepts string literal values that are
/// similar to `format!`'s string literal. See the [reference] for details on what is permitted
/// in this string literal.
///
/// [reference]: https://doc.rust-lang.org/nightly/reference/attributes/diagnostics.html#the-diagnostic-tool-attribute-namespace
pub MALFORMED_DIAGNOSTIC_FORMAT_LITERALS,
Warn,
"detects diagnostic attribute with malformed diagnostic format literals",
}
declare_lint! {
/// The `ambiguous_glob_imports` lint detects glob imports that should report ambiguity
/// errors, but previously didn't do that due to rustc bugs.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(ambiguous_glob_imports)]
/// pub fn foo() -> u32 {
/// use sub::*;
/// C
/// }
///
/// mod sub {
/// mod mod1 { pub const C: u32 = 1; }
/// mod mod2 { pub const C: u32 = 2; }
///
/// pub use mod1::*;
/// pub use mod2::*;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous versions of Rust compile it successfully because it
/// had lost the ambiguity error when resolve `use sub::mod2::*`.
///
/// This is a [future-incompatible] lint to transition this to a
/// hard error in the future.
///
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub AMBIGUOUS_GLOB_IMPORTS,
Deny,
"detects certain glob imports that require reporting an ambiguity error",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #114095 <https://github.com/rust-lang/rust/issues/114095>",
report_in_deps: true,
};
}
declare_lint! {
/// The `refining_impl_trait_reachable` lint detects `impl Trait` return
/// types in method signatures that are refined by a publically reachable
/// trait implementation, meaning the implementation adds information about
/// the return type that is not present in the trait.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(refining_impl_trait)]
///
/// use std::fmt::Display;
///
/// pub trait AsDisplay {
/// fn as_display(&self) -> impl Display;
/// }
///
/// impl<'s> AsDisplay for &'s str {
/// fn as_display(&self) -> Self {
/// *self
/// }
/// }
///
/// fn main() {
/// // users can observe that the return type of
/// // `<&str as AsDisplay>::as_display()` is `&str`.
/// let _x: &str = "".as_display();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Callers of methods for types where the implementation is known are
/// able to observe the types written in the impl signature. This may be
/// intended behavior, but may also lead to implementation details being
/// revealed unintentionally. In particular, it may pose a semver hazard
/// for authors of libraries who do not wish to make stronger guarantees
/// about the types than what is written in the trait signature.
///
/// `refining_impl_trait` is a lint group composed of two lints:
///
/// * `refining_impl_trait_reachable`, for refinements that are publically
/// reachable outside a crate, and
/// * `refining_impl_trait_internal`, for refinements that are only visible
/// within a crate.
///
/// We are seeking feedback on each of these lints; see issue
/// [#121718](https://github.com/rust-lang/rust/issues/121718) for more
/// information.
pub REFINING_IMPL_TRAIT_REACHABLE,
Warn,
"impl trait in impl method signature does not match trait method signature",
}
declare_lint! {
/// The `refining_impl_trait_internal` lint detects `impl Trait` return
/// types in method signatures that are refined by a trait implementation,
/// meaning the implementation adds information about the return type that
/// is not present in the trait.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(refining_impl_trait)]
///
/// use std::fmt::Display;
///
/// trait AsDisplay {
/// fn as_display(&self) -> impl Display;
/// }
///
/// impl<'s> AsDisplay for &'s str {
/// fn as_display(&self) -> Self {
/// *self
/// }
/// }
///
/// fn main() {
/// // users can observe that the return type of
/// // `<&str as AsDisplay>::as_display()` is `&str`.
/// let _x: &str = "".as_display();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Callers of methods for types where the implementation is known are
/// able to observe the types written in the impl signature. This may be
/// intended behavior, but may also lead to implementation details being
/// revealed unintentionally. In particular, it may pose a semver hazard
/// for authors of libraries who do not wish to make stronger guarantees
/// about the types than what is written in the trait signature.
///
/// `refining_impl_trait` is a lint group composed of two lints:
///
/// * `refining_impl_trait_reachable`, for refinements that are publically
/// reachable outside a crate, and
/// * `refining_impl_trait_internal`, for refinements that are only visible
/// within a crate.
///
/// We are seeking feedback on each of these lints; see issue
/// [#121718](https://github.com/rust-lang/rust/issues/121718) for more
/// information.
pub REFINING_IMPL_TRAIT_INTERNAL,
Warn,
"impl trait in impl method signature does not match trait method signature",
}
declare_lint! {
/// The `elided_lifetimes_in_associated_constant` lint detects elided lifetimes
/// in associated constants when there are other lifetimes in scope. This was
/// accidentally supported, and this lint was later relaxed to allow eliding
/// lifetimes to `'static` when there are no lifetimes in scope.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(elided_lifetimes_in_associated_constant)]
///
/// struct Foo<'a>(&'a ());
///
/// impl<'a> Foo<'a> {
/// const STR: &str = "hello, world";
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous version of Rust
///
/// Implicit static-in-const behavior was decided [against] for associated
/// constants because of ambiguity. This, however, regressed and the compiler
/// erroneously treats elided lifetimes in associated constants as lifetime
/// parameters on the impl.
///
/// This is a [future-incompatible] lint to transition this to a
/// hard error in the future.
///
/// [against]: https://github.com/rust-lang/rust/issues/38831
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
Deny,
"elided lifetimes cannot be used in associated constants in impls",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #115010 <https://github.com/rust-lang/rust/issues/115010>",
};
}
declare_lint! {
/// The `private_macro_use` lint detects private macros that are imported
/// with `#[macro_use]`.
///
/// ### Example
///
/// ```rust,ignore (needs extern crate)
/// // extern_macro.rs
/// macro_rules! foo_ { () => {}; }
/// use foo_ as foo;
///
/// // code.rs
///
/// #![deny(private_macro_use)]
///
/// #[macro_use]
/// extern crate extern_macro;
///
/// fn main() {
/// foo!();
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// error: cannot find macro `foo` in this scope
/// ```
///
/// ### Explanation
///
/// This lint arises from overlooking visibility checks for macros
/// in an external crate.
///
/// This is a [future-incompatible] lint to transition this to a
/// hard error in the future.
///
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub PRIVATE_MACRO_USE,
Deny,
"detects certain macro bindings that should not be re-exported",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #120192 <https://github.com/rust-lang/rust/issues/120192>",
report_in_deps: true,
};
}
declare_lint! {
/// The `uncovered_param_in_projection` lint detects a violation of one of Rust's orphan rules for
/// foreign trait implementations that concerns the use of type parameters inside trait associated
/// type paths ("projections") whose output may not be a local type that is mistakenly considered
/// to "cover" said parameters which is **unsound** and which may be rejected by a future version
/// of the compiler.
///
/// Originally reported in [#99554].
///
/// [#99554]: https://github.com/rust-lang/rust/issues/99554
///
/// ### Example
///
/// ```rust,ignore (dependent)
/// // dependency.rs
/// #![crate_type = "lib"]
///
/// pub trait Trait<T, U> {}
/// ```
///
/// ```edition2021,ignore (needs dependency)
/// // dependent.rs
/// trait Identity {
/// type Output;
/// }
///
/// impl<T> Identity for T {
/// type Output = T;
/// }
///
/// struct Local;
///
/// impl<T> dependency::Trait<Local, T> for <T as Identity>::Output {}
///
/// fn main() {}
/// ```
///
/// This will produce:
///
/// ```text
/// warning[E0210]: type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
/// --> dependent.rs:11:6
/// |
/// 11 | impl<T> dependency::Trait<Local, T> for <T as Identity>::Output {}
/// | ^ type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
/// |
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #124559 <https://github.com/rust-lang/rust/issues/124559>
/// = note: implementing a foreign trait is only possible if at least one of the types for which it is implemented is local, and no uncovered type parameters appear before that first local type
/// = note: in this case, 'before' refers to the following order: `impl<..> ForeignTrait<T1, ..., Tn> for T0`, where `T0` is the first and `Tn` is the last
/// = note: `#[warn(uncovered_param_in_projection)]` on by default
/// ```
///
/// ### Explanation
///
/// FIXME(fmease): Write explainer.
pub UNCOVERED_PARAM_IN_PROJECTION,
Warn,
"impl contains type parameters that are not covered",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #124559 <https://github.com/rust-lang/rust/issues/124559>",
};
}
declare_lint! {
/// The `deprecated_safe_2024` lint detects unsafe functions being used as
/// safe functions.
///
/// ### Example
///
/// ```rust,edition2021,compile_fail
/// #![deny(deprecated_safe)]
/// // edition 2021
/// use std::env;
/// fn enable_backtrace() {
/// env::set_var("RUST_BACKTRACE", "1");
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Rust [editions] allow the language to evolve without breaking backward
/// compatibility. This lint catches code that uses `unsafe` functions that
/// were declared as safe (non-`unsafe`) in editions prior to Rust 2024. If
/// you switch the compiler to Rust 2024 without updating the code, then it
/// will fail to compile if you are using a function previously marked as
/// safe.
///
/// You can audit the code to see if it suffices the preconditions of the
/// `unsafe` code, and if it does, you can wrap it in an `unsafe` block. If
/// you can't fulfill the preconditions, you probably need to switch to a
/// different way of doing what you want to achieve.
///
/// This lint can automatically wrap the calls in `unsafe` blocks, but this
/// obviously cannot verify that the preconditions of the `unsafe`
/// functions are fulfilled, so that is still up to the user.
///
/// The lint is currently "allow" by default, but that might change in the
/// future.
///
/// [editions]: https://doc.rust-lang.org/edition-guide/
pub DEPRECATED_SAFE_2024,
Allow,
"detects unsafe functions being used as safe functions",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2024),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2024/newly-unsafe-functions.html>",
};
}
declare_lint! {
/// The `missing_unsafe_on_extern` lint detects missing unsafe keyword on extern declarations.
///
/// ### Example
///
/// ```rust,edition2021
/// #![warn(missing_unsafe_on_extern)]
/// #![allow(dead_code)]
///
/// extern "C" {
/// fn foo(_: i32);
/// }
///
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Declaring extern items, even without ever using them, can cause Undefined Behavior. We
/// should consider all sources of Undefined Behavior to be unsafe.
///
/// This is a [future-incompatible] lint to transition this to a
/// hard error in the future.
///
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub MISSING_UNSAFE_ON_EXTERN,
Allow,
"detects missing unsafe keyword on extern declarations",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2024),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-extern.html>",
};
}
declare_lint! {
/// The `unsafe_attr_outside_unsafe` lint detects a missing unsafe keyword
/// on attributes considered unsafe.
///
/// ### Example
///
/// ```rust,edition2021
/// #![warn(unsafe_attr_outside_unsafe)]
///
/// #[no_mangle]
/// extern "C" fn foo() {}
///
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Some attributes (e.g. `no_mangle`, `export_name`, `link_section` -- see
/// [issue #82499] for a more complete list) are considered "unsafe" attributes.
/// An unsafe attribute must only be used inside unsafe(...).
///
/// This lint can automatically wrap the attributes in `unsafe(...)` , but this
/// obviously cannot verify that the preconditions of the `unsafe`
/// attributes are fulfilled, so that is still up to the user.
///
/// The lint is currently "allow" by default, but that might change in the
/// future.
///
/// [editions]: https://doc.rust-lang.org/edition-guide/
/// [issue #82499]: https://github.com/rust-lang/rust/issues/82499
pub UNSAFE_ATTR_OUTSIDE_UNSAFE,
Allow,
"detects unsafe attributes outside of unsafe",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2024),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-attributes.html>",
};
}
declare_lint! {
/// The `out_of_scope_macro_calls` lint detects `macro_rules` called when they are not in scope,
/// above their definition, which may happen in key-value attributes.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![doc = in_root!()]
///
/// macro_rules! in_root { () => { "" } }
///
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The scope in which a `macro_rules` item is visible starts at that item and continues
/// below it. This is more similar to `let` than to other items, which are in scope both above
/// and below their definition.
/// Due to a bug `macro_rules` were accidentally in scope inside some key-value attributes
/// above their definition. The lint catches such cases.
/// To address the issue turn the `macro_rules` into a regularly scoped item by importing it
/// with `use`.
///
/// This is a [future-incompatible] lint to transition this to a
/// hard error in the future.
///
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub OUT_OF_SCOPE_MACRO_CALLS,
Deny,
"detects out of scope calls to `macro_rules` in key-value attributes",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #124535 <https://github.com/rust-lang/rust/issues/124535>",
report_in_deps: true,
};
}
declare_lint! {
/// The `supertrait_item_shadowing_usage` lint detects when the
/// usage of an item that is provided by both a subtrait and supertrait
/// is shadowed, preferring the subtrait.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![feature(supertrait_item_shadowing)]
/// #![deny(supertrait_item_shadowing_usage)]
///
/// trait Upstream {
/// fn hello(&self) {}
/// }
/// impl<T> Upstream for T {}
///
/// trait Downstream: Upstream {
/// fn hello(&self) {}
/// }
/// impl<T> Downstream for T {}
///
/// struct MyType;
/// MyType.hello();
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// RFC 3624 specified a heuristic in which a supertrait item would be
/// shadowed by a subtrait item when ambiguity occurs during item
/// selection. In order to mitigate side-effects of this happening
/// silently, this lint detects these cases when users want to deny them
/// or fix the call sites.
pub SUPERTRAIT_ITEM_SHADOWING_USAGE,
// FIXME(supertrait_item_shadowing): It is not decided if this should
// warn by default at the call site.
Allow,
"detects when a supertrait item is shadowed by a subtrait item",
@feature_gate = supertrait_item_shadowing;
}
declare_lint! {
/// The `supertrait_item_shadowing_definition` lint detects when the
/// definition of an item that is provided by both a subtrait and
/// supertrait is shadowed, preferring the subtrait.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![feature(supertrait_item_shadowing)]
/// #![deny(supertrait_item_shadowing_definition)]
///
/// trait Upstream {
/// fn hello(&self) {}
/// }
/// impl<T> Upstream for T {}
///
/// trait Downstream: Upstream {
/// fn hello(&self) {}
/// }
/// impl<T> Downstream for T {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// RFC 3624 specified a heuristic in which a supertrait item would be
/// shadowed by a subtrait item when ambiguity occurs during item
/// selection. In order to mitigate side-effects of this happening
/// silently, this lint detects these cases when users want to deny them
/// or fix their trait definitions.
pub SUPERTRAIT_ITEM_SHADOWING_DEFINITION,
// FIXME(supertrait_item_shadowing): It is not decided if this should
// warn by default at the usage site.
Allow,
"detects when a supertrait item is shadowed by a subtrait item",
@feature_gate = supertrait_item_shadowing;
}
declare_lint! {
/// The `tail_expr_drop_order` lint looks for those values generated at the tail expression location,
/// that runs a custom `Drop` destructor.
/// Some of them may be dropped earlier in Edition 2024 that they used to in Edition 2021 and prior.
/// This lint detects those cases and provides you information on those values and their custom destructor implementations.
/// Your discretion on this information is required.
///
/// ### Example
/// ```rust,edition2021
/// #![warn(tail_expr_drop_order)]
/// struct Droppy(i32);
/// impl Droppy {
/// fn get(&self) -> i32 {
/// self.0
/// }
/// }
/// impl Drop for Droppy {
/// fn drop(&mut self) {
/// // This is a custom destructor and it induces side-effects that is observable
/// // especially when the drop order at a tail expression changes.
/// println!("loud drop {}", self.0);
/// }
/// }
/// fn edition_2021() -> i32 {
/// let another_droppy = Droppy(0);
/// Droppy(1).get()
/// }
/// fn main() {
/// edition_2021();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In tail expression of blocks or function bodies,
/// values of type with significant `Drop` implementation has an ill-specified drop order
/// before Edition 2024 so that they are dropped only after dropping local variables.
/// Edition 2024 introduces a new rule with drop orders for them,
/// so that they are dropped first before dropping local variables.
///
/// A significant `Drop::drop` destructor here refers to an explicit, arbitrary
/// implementation of the `Drop` trait on the type, with exceptions including `Vec`,
/// `Box`, `Rc`, `BTreeMap` and `HashMap` that are marked by the compiler otherwise
/// so long that the generic types have no significant destructor recursively.
/// In other words, a type has a significant drop destructor when it has a `Drop` implementation
/// or its destructor invokes a significant destructor on a type.
/// Since we cannot completely reason about the change by just inspecting the existence of
/// a significant destructor, this lint remains only a suggestion and is set to `allow` by default.
///
/// This lint only points out the issue with `Droppy`, which will be dropped before `another_droppy`
/// does in Edition 2024.
/// No fix will be proposed by this lint.
/// However, the most probable fix is to hoist `Droppy` into its own local variable binding.
/// ```rust
/// struct Droppy(i32);
/// impl Droppy {
/// fn get(&self) -> i32 {
/// self.0
/// }
/// }
/// fn edition_2024() -> i32 {
/// let value = Droppy(0);
/// let another_droppy = Droppy(1);
/// value.get()
/// }
/// ```
pub TAIL_EXPR_DROP_ORDER,
Allow,
"Detect and warn on significant change in drop order in tail expression location",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2024),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2024/temporary-tail-expr-scope.html>",
};
}
declare_lint! {
/// The `rust_2024_guarded_string_incompatible_syntax` lint detects `#` tokens
/// that will be parsed as part of a guarded string literal in Rust 2024.
///
/// ### Example
///
/// ```rust,edition2021,compile_fail
/// #![deny(rust_2024_guarded_string_incompatible_syntax)]
///
/// macro_rules! m {
/// (# $x:expr #) => ();
/// (# $x:expr) => ();
/// }
///
/// m!(#"hey"#);
/// m!(#"hello");
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Prior to Rust 2024, `#"hey"#` is three tokens: the first `#`
/// followed by the string literal `"hey"` then the final `#`.
/// In Rust 2024, the whole sequence is considered a single token.
///
/// This lint suggests to add whitespace between the leading `#`
/// and the string to keep them separated in Rust 2024.
// Allow this lint -- rustdoc doesn't yet support threading edition into this lint's parser.
#[allow(rustdoc::invalid_rust_codeblocks)]
pub RUST_2024_GUARDED_STRING_INCOMPATIBLE_SYNTAX,
Allow,
"will be parsed as a guarded string in Rust 2024",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2024),
reference: "<https://doc.rust-lang.org/edition-guide/rust-2024/reserved-syntax.html>",
};
crate_level_only
}
declare_lint! {
/// The `aarch64_softfloat_neon` lint detects usage of `#[target_feature(enable = "neon")]` on
/// softfloat aarch64 targets. Enabling this target feature causes LLVM to alter the ABI of
/// function calls, making this attribute unsound to use.
///
/// ### Example
///
/// ```rust,ignore (needs aarch64-unknown-none-softfloat)
/// #[target_feature(enable = "neon")]
/// fn with_neon() {}
/// ```
///
/// This will produce:
///
/// ```text
/// error: enabling the `neon` target feature on the current target is unsound due to ABI issues
/// --> $DIR/abi-incompatible-target-feature-attribute-fcw.rs:11:18
/// |
/// | #[target_feature(enable = "neon")]
/// | ^^^^^^^^^^^^^^^
/// |
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #134375 <https://github.com/rust-lang/rust/issues/134375>
/// ```
///
/// ### Explanation
///
/// If a function like `with_neon` above ends up containing calls to LLVM builtins, those will
/// not use the correct ABI. This is caused by a lack of support in LLVM for mixing code with
/// and without the `neon` target feature. The target feature should never have been stabilized
/// on this target due to this issue, but the problem was not known at the time of
/// stabilization.
pub AARCH64_SOFTFLOAT_NEON,
Warn,
"detects code that could be affected by ABI issues on aarch64 softfloat targets",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseError,
reference: "issue #134375 <https://github.com/rust-lang/rust/issues/134375>",
report_in_deps: true,
};
}