clippy_lints/src/attrs.rs

//! checks for attributes

use reexport::*;
use rustc::lint::*;
use rustc::hir::*;
use semver::Version;
use syntax::ast::{Attribute, Lit, LitKind, MetaItemKind, NestedMetaItem, NestedMetaItemKind};
use syntax::codemap::Span;
use utils::{in_macro, match_def_path, resolve_node, paths, span_lint, span_lint_and_then, snippet_opt};

/// **What it does:** Checks for items annotated with `#[inline(always)]`,
/// unless the annotated function is empty or simply panics.
///
/// **Why is this bad?** While there are valid uses of this annotation (and once
/// you know when to use it, by all means `allow` this lint), it's a common
/// newbie-mistake to pepper one's code with it.
///
/// As a rule of thumb, before slapping `#[inline(always)]` on a function,
/// measure if that additional function call really affects your runtime profile
/// sufficiently to make up for the increase in compile time.
///
/// **Known problems:** False positives, big time. This lint is meant to be
/// deactivated by everyone doing serious performance work. This means having
/// done the measurement.
///
/// **Example:**
/// ```rust
/// #[inline(always)]
/// fn not_quite_hot_code(..) { ... }
/// ```
declare_lint! {
    pub INLINE_ALWAYS,
    Warn,
    "use of `#[inline(always)]`"
}

/// **What it does:** Checks for `extern crate` and `use` items annotated with lint attributes
///
/// **Why is this bad?** Lint attributes have no effect on crate imports. Most likely a `!` was forgotten
///
/// **Known problems:** Technically one might allow `unused_import` on a `use` item, but it's easier to remove the unused item.
///
/// **Example:**
/// ```rust
/// #[deny(dead_code)]
/// extern crate foo;
/// #[allow(unused_import)]
/// use foo::bar;
/// ```
declare_lint! {
    pub USELESS_ATTRIBUTE,
    Warn,
    "use of lint attributes on `extern crate` items"
}

/// **What it does:** Checks for `#[deprecated]` annotations with a `since`
/// field that is not a valid semantic version.
///
/// **Why is this bad?** For checking the version of the deprecation, it must be
/// a valid semver. Failing that, the contained information is useless.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// #[deprecated(since = "forever")]
/// fn something_else(..) { ... }
/// ```
declare_lint! {
    pub DEPRECATED_SEMVER,
    Warn,
    "use of `#[deprecated(since = \"x\")]` where x is not semver"
}

#[derive(Copy,Clone)]
pub struct AttrPass;

impl LintPass for AttrPass {
    fn get_lints(&self) -> LintArray {
        lint_array!(INLINE_ALWAYS, DEPRECATED_SEMVER, USELESS_ATTRIBUTE)
    }
}

impl LateLintPass for AttrPass {
    fn check_attribute(&mut self, cx: &LateContext, attr: &Attribute) {
        if let MetaItemKind::List(ref items) = attr.value.node {
            if items.is_empty() || attr.name() != "deprecated" {
                return;
            }
            for item in items {
                if_let_chain! {[
                    let NestedMetaItemKind::MetaItem(ref mi) = item.node,
                    let MetaItemKind::NameValue(ref lit) = mi.node,
                    mi.name() == "since",
                ], {
                    check_semver(cx, item.span, lit);
                }}
            }
        }
    }

    fn check_item(&mut self, cx: &LateContext, item: &Item) {
        if is_relevant_item(cx, item) {
            check_attrs(cx, item.span, &item.name, &item.attrs)
        }
        match item.node {
            ItemExternCrate(_) |
            ItemUse(_) => {
                for attr in &item.attrs {
                    if let MetaItemKind::List(ref lint_list) = attr.value.node {
                        match &*attr.name().as_str() {
                            "allow" | "warn" | "deny" | "forbid" => {
                                // whitelist `unused_imports`
                                for lint in lint_list {
                                    if is_word(lint, "unused_imports") {
                                        if let ItemUse(_) = item.node {
                                            return;
                                        }
                                    }
                                }
                                if let Some(mut sugg) = snippet_opt(cx, attr.span) {
                                    if sugg.len() > 1 {
                                        span_lint_and_then(cx, USELESS_ATTRIBUTE, attr.span,
                                                           "useless lint attribute",
                                                           |db| {
                                            sugg.insert(1, '!');
                                            db.span_suggestion(attr.span, "if you just forgot a `!`, use", sugg);
                                        });
                                    }
                                }
                            },
                            _ => {},
                        }
                    }
                }
            },
            _ => {},
        }
    }

    fn check_impl_item(&mut self, cx: &LateContext, item: &ImplItem) {
        if is_relevant_impl(cx, item) {
            check_attrs(cx, item.span, &item.name, &item.attrs)
        }
    }

    fn check_trait_item(&mut self, cx: &LateContext, item: &TraitItem) {
        if is_relevant_trait(cx, item) {
            check_attrs(cx, item.span, &item.name, &item.attrs)
        }
    }
}

fn is_relevant_item(cx: &LateContext, item: &Item) -> bool {
    if let ItemFn(_, _, _, _, _, ref expr) = item.node {
        is_relevant_expr(cx, expr)
    } else {
        false
    }
}

fn is_relevant_impl(cx: &LateContext, item: &ImplItem) -> bool {
    match item.node {
        ImplItemKind::Method(_, ref expr) => is_relevant_expr(cx, expr),
        _ => false,
    }
}

fn is_relevant_trait(cx: &LateContext, item: &TraitItem) -> bool {
    match item.node {
        MethodTraitItem(_, None) => true,
        MethodTraitItem(_, Some(ref expr)) => is_relevant_expr(cx, expr),
        _ => false,
    }
}

fn is_relevant_block(cx: &LateContext, block: &Block) -> bool {
    for stmt in &block.stmts {
        match stmt.node {
            StmtDecl(_, _) => return true,
            StmtExpr(ref expr, _) |
            StmtSemi(ref expr, _) => {
                return is_relevant_expr(cx, expr);
            }
        }
    }
    block.expr.as_ref().map_or(false, |e| is_relevant_expr(cx, e))
}

fn is_relevant_expr(cx: &LateContext, expr: &Expr) -> bool {
    match expr.node {
        ExprBlock(ref block) => is_relevant_block(cx, block),
        ExprRet(Some(ref e)) => is_relevant_expr(cx, e),
        ExprRet(None) | ExprBreak(_, None) => false,
        ExprCall(ref path_expr, _) => {
            if let ExprPath(..) = path_expr.node {
                let fun_id = resolve_node(cx, path_expr.id).expect("function should be resolved").def_id();
                !match_def_path(cx, fun_id, &paths::BEGIN_PANIC)
            } else {
                true
            }
        }
        _ => true,
    }
}

fn check_attrs(cx: &LateContext, span: Span, name: &Name, attrs: &[Attribute]) {
    if in_macro(cx, span) {
        return;
    }

    for attr in attrs {
        if let MetaItemKind::List(ref values) = attr.value.node {
            if values.len() != 1 || attr.name() != "inline" {
                continue;
            }
            if is_word(&values[0], "always") {
                span_lint(cx,
                          INLINE_ALWAYS,
                          attr.span,
                          &format!("you have declared `#[inline(always)]` on `{}`. This is usually a bad idea",
                                   name));
            }
        }
    }
}

fn check_semver(cx: &LateContext, span: Span, lit: &Lit) {
    if let LitKind::Str(ref is, _) = lit.node {
        if Version::parse(&*is.as_str()).is_ok() {
            return;
        }
    }
    span_lint(cx,
              DEPRECATED_SEMVER,
              span,
              "the since field must contain a semver-compliant version");
}

fn is_word(nmi: &NestedMetaItem, expected: &str) -> bool {
    if let NestedMetaItemKind::MetaItem(ref mi) = nmi.node {
        mi.is_word() && mi.name() == expected
    } else {
        false
    }
}