compiler/rustc_lint/src/levels.rs

use rustc_ast as ast;
use rustc_ast::{DUMMY_NODE_ID, NodeId};
use rustc_attr_parsing::AttributeParser;
use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
use rustc_data_structures::unord::UnordSet;
use rustc_errors::{Diag, DiagCtxtHandle, Diagnostic, MultiSpan, msg};
use rustc_feature::{Features, GateIssue};
use rustc_hir::attrs::{LintAttribute, LintAttributeKind, LintInstance};
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::{self as hir, HirId, Target, find_attr};
use rustc_index::IndexVec;
use rustc_middle::bug;
use rustc_middle::hir::nested_filter;
use rustc_middle::lint::{
    LevelAndSource, LintExpectation, LintLevelSource, ShallowLintLevelMap, emit_lint_base,
    reveal_actual_level,
};
use rustc_middle::query::Providers;
use rustc_middle::ty::{RegisteredTools, TyCtxt};
use rustc_session::Session;
use rustc_session::lint::builtin::{
    self, FORBIDDEN_LINT_GROUPS, RENAMED_AND_REMOVED_LINTS, SINGLE_USE_LIFETIMES,
    UNFULFILLED_LINT_EXPECTATIONS, UNKNOWN_LINTS,
};
use rustc_session::lint::{
    CheckLintNameResult, Level, Lint, LintExpectationId, LintId, TargetLint,
};
use rustc_span::{DUMMY_SP, Span, Symbol, sym};
use tracing::{debug, instrument};

use crate::builtin::MISSING_DOCS;
use crate::context::LintStore;
use crate::errors::{
    CheckNameUnknownTool, OverruledAttribute, OverruledAttributeSub, RequestedLevel,
    UnsupportedGroup,
};
use crate::late::unerased_lint_store;
use crate::lints::{
    DeprecatedLintNameFromCommandLine, OverruledAttributeLint, RemovedLintFromCommandLine,
    RenamedLintFromCommandLine, RenamedLintSuggestion, UnknownLintFromCommandLine,
    UnknownLintSuggestion,
};

const ALLOW_LISTED_ATTRS: &[Symbol] = &[
    sym::allow,
    sym::deny,
    sym::expect,
    sym::forbid,
    sym::warn,
    sym::automatically_derived,
    sym::doc,
];

/// Collection of lint levels for the whole crate.
/// This is used by AST-based lints, which do not
/// wait until we have built HIR to be emitted.
#[derive(Debug)]
struct LintLevelSets {
    /// Linked list of specifications.
    list: IndexVec<LintStackIndex, LintSet>,
}

rustc_index::newtype_index! {
    struct LintStackIndex {
        const COMMAND_LINE = 0;
    }
}

/// Specifications found at this position in the stack. This map only represents the lints
/// found for one set of attributes (like `shallow_lint_levels_on` does).
///
/// We store the level specifications as a linked list.
/// Each `LintSet` represents a set of attributes on the same AST node.
/// The `parent` forms a linked list that matches the AST tree.
/// This way, walking the linked list is equivalent to walking the AST bottom-up
/// to find the specifications for a given lint.
#[derive(Debug)]
struct LintSet {
    // -A,-W,-D flags, a `Symbol` for the flag itself and `Level` for which
    // flag.
    specs: FxIndexMap<LintId, LevelAndSource>,
    parent: LintStackIndex,
}

impl LintLevelSets {
    fn new() -> Self {
        LintLevelSets { list: IndexVec::new() }
    }

    fn get_lint_level(
        &self,
        lint: &'static Lint,
        idx: LintStackIndex,
        aux: Option<&FxIndexMap<LintId, LevelAndSource>>,
        sess: &Session,
    ) -> LevelAndSource {
        let lint = LintId::of(lint);
        let (level, mut src) = self.raw_lint_id_level(lint, idx, aux);
        let (level, lint_id) = reveal_actual_level(level, &mut src, sess, lint, |id| {
            self.raw_lint_id_level(id, idx, aux)
        });
        LevelAndSource { level, lint_id, src }
    }

    fn raw_lint_id_level(
        &self,
        id: LintId,
        mut idx: LintStackIndex,
        aux: Option<&FxIndexMap<LintId, LevelAndSource>>,
    ) -> (Option<(Level, Option<LintExpectationId>)>, LintLevelSource) {
        if let Some(specs) = aux
            && let Some(&LevelAndSource { level, lint_id, src }) = specs.get(&id)
        {
            return (Some((level, lint_id)), src);
        }

        loop {
            let LintSet { ref specs, parent } = self.list[idx];
            if let Some(&LevelAndSource { level, lint_id, src }) = specs.get(&id) {
                return (Some((level, lint_id)), src);
            }
            if idx == COMMAND_LINE {
                return (None, LintLevelSource::Default);
            }
            idx = parent;
        }
    }
}

fn lints_that_dont_need_to_run(tcx: TyCtxt<'_>, (): ()) -> UnordSet<LintId> {
    let store = unerased_lint_store(&tcx.sess);
    let root_map = tcx.shallow_lint_levels_on(hir::CRATE_OWNER_ID);

    let mut dont_need_to_run: FxHashSet<LintId> = store
        .get_lints()
        .into_iter()
        .filter(|lint| {
            // Lints that show up in future-compat reports must always be run.
            let has_future_breakage =
                lint.future_incompatible.is_some_and(|fut| fut.report_in_deps);
            !has_future_breakage && !lint.eval_always
        })
        .filter(|lint| {
            let lint_level =
                root_map.lint_level_id_at_node(tcx, LintId::of(lint), hir::CRATE_HIR_ID);
            // Only include lints that are allowed at crate root or by default.
            matches!(lint_level.level, Level::Allow)
                || (matches!(lint_level.src, LintLevelSource::Default)
                    && lint.default_level(tcx.sess.edition()) == Level::Allow)
        })
        .map(|lint| LintId::of(*lint))
        .collect();

    for owner in tcx.hir_crate_items(()).owners() {
        let map = tcx.shallow_lint_levels_on(owner);

        // All lints that appear with a non-allow level must be run.
        for (_, specs) in map.specs.iter() {
            for (lint, level_and_source) in specs.iter() {
                if !matches!(level_and_source.level, Level::Allow) {
                    dont_need_to_run.remove(lint);
                }
            }
        }
    }

    dont_need_to_run.into()
}

#[instrument(level = "trace", skip(tcx), ret)]
fn shallow_lint_levels_on(tcx: TyCtxt<'_>, owner: hir::OwnerId) -> ShallowLintLevelMap {
    let store = unerased_lint_store(tcx.sess);
    let attrs = tcx.hir_attr_map(owner);

    let mut levels = LintLevelsBuilder {
        sess: tcx.sess,
        features: tcx.features(),
        provider: LintLevelQueryMap {
            tcx,
            cur: owner.into(),
            specs: ShallowLintLevelMap::default(),
            empty: FxIndexMap::default(),
            attrs,
        },
        lint_added_lints: false,
        store,
        registered_tools: tcx.registered_tools(()),
    };

    if owner == hir::CRATE_OWNER_ID {
        levels.add_command_line();
    }

    match attrs.map.range(..) {
        // There is only something to do if there are attributes at all.
        [] => {}
        // Most of the time, there is only one attribute. Avoid fetching HIR in that case.
        &[(local_id, _)] => levels.add_id(HirId { owner, local_id }),
        // Otherwise, we need to visit the attributes in source code order, so we fetch HIR and do
        // a standard visit.
        // FIXME(#102522) Just iterate on attrs once that iteration order matches HIR's.
        _ => match tcx.hir_owner_node(owner) {
            hir::OwnerNode::Item(item) => levels.visit_item(item),
            hir::OwnerNode::ForeignItem(item) => levels.visit_foreign_item(item),
            hir::OwnerNode::TraitItem(item) => levels.visit_trait_item(item),
            hir::OwnerNode::ImplItem(item) => levels.visit_impl_item(item),
            hir::OwnerNode::Crate(mod_) => {
                levels.add_id(hir::CRATE_HIR_ID);
                levels.visit_mod(mod_, mod_.spans.inner_span, hir::CRATE_HIR_ID)
            }
            hir::OwnerNode::Synthetic => unreachable!(),
        },
    }

    let specs = levels.provider.specs;

    #[cfg(debug_assertions)]
    for (_, v) in specs.specs.iter() {
        debug_assert!(!v.is_empty());
    }

    specs
}

pub struct TopDown {
    sets: LintLevelSets,
    cur: LintStackIndex,
}

pub trait LintLevelsProvider {
    fn current_specs(&self) -> &FxIndexMap<LintId, LevelAndSource>;
    fn insert(&mut self, id: LintId, lvl: LevelAndSource);
    fn get_lint_level(&self, lint: &'static Lint, sess: &Session) -> LevelAndSource;
    fn push_expectation(&mut self, id: LintExpectationId, expectation: LintExpectation);
}

impl LintLevelsProvider for TopDown {
    fn current_specs(&self) -> &FxIndexMap<LintId, LevelAndSource> {
        &self.sets.list[self.cur].specs
    }

    fn insert(&mut self, id: LintId, lvl: LevelAndSource) {
        self.sets.list[self.cur].specs.insert(id, lvl);
    }

    fn get_lint_level(&self, lint: &'static Lint, sess: &Session) -> LevelAndSource {
        self.sets.get_lint_level(lint, self.cur, Some(self.current_specs()), sess)
    }

    fn push_expectation(&mut self, _: LintExpectationId, _: LintExpectation) {}
}

struct LintLevelQueryMap<'tcx> {
    tcx: TyCtxt<'tcx>,
    cur: HirId,
    specs: ShallowLintLevelMap,
    /// Empty hash map to simplify code.
    empty: FxIndexMap<LintId, LevelAndSource>,
    attrs: &'tcx hir::AttributeMap<'tcx>,
}

impl LintLevelsProvider for LintLevelQueryMap<'_> {
    fn current_specs(&self) -> &FxIndexMap<LintId, LevelAndSource> {
        self.specs.specs.get(&self.cur.local_id).unwrap_or(&self.empty)
    }
    fn insert(&mut self, id: LintId, lvl: LevelAndSource) {
        self.specs.specs.get_mut_or_insert_default(self.cur.local_id).insert(id, lvl);
    }
    fn get_lint_level(&self, lint: &'static Lint, _: &Session) -> LevelAndSource {
        self.specs.lint_level_id_at_node(self.tcx, LintId::of(lint), self.cur)
    }
    fn push_expectation(&mut self, id: LintExpectationId, expectation: LintExpectation) {
        self.specs.expectations.push((id, expectation))
    }
}

impl<'tcx> LintLevelsBuilder<'_, LintLevelQueryMap<'tcx>> {
    fn add_id(&mut self, hir_id: HirId) {
        self.provider.cur = hir_id;
        self.add(self.provider.attrs.get(hir_id.local_id), Some(hir_id));
    }
}

impl<'tcx> Visitor<'tcx> for LintLevelsBuilder<'_, LintLevelQueryMap<'tcx>> {
    type NestedFilter = nested_filter::OnlyBodies;

    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
        self.provider.tcx
    }

    fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
        self.add_id(param.hir_id);
        intravisit::walk_param(self, param);
    }

    fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) {
        self.add_id(it.hir_id());
        intravisit::walk_item(self, it);
    }

    fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {
        self.add_id(it.hir_id());
        intravisit::walk_foreign_item(self, it);
    }

    fn visit_stmt(&mut self, s: &'tcx hir::Stmt<'tcx>) {
        self.add_id(s.hir_id);
        intravisit::walk_stmt(self, s);
    }

    fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
        self.add_id(e.hir_id);
        intravisit::walk_expr(self, e);
    }

    fn visit_pat_field(&mut self, f: &'tcx hir::PatField<'tcx>) -> Self::Result {
        self.add_id(f.hir_id);
        intravisit::walk_pat_field(self, f);
    }

    fn visit_expr_field(&mut self, f: &'tcx hir::ExprField<'tcx>) {
        self.add_id(f.hir_id);
        intravisit::walk_expr_field(self, f);
    }

    fn visit_field_def(&mut self, s: &'tcx hir::FieldDef<'tcx>) {
        self.add_id(s.hir_id);
        intravisit::walk_field_def(self, s);
    }

    fn visit_variant(&mut self, v: &'tcx hir::Variant<'tcx>) {
        self.add_id(v.hir_id);
        intravisit::walk_variant(self, v);
    }

    fn visit_local(&mut self, l: &'tcx hir::LetStmt<'tcx>) {
        self.add_id(l.hir_id);
        intravisit::walk_local(self, l);
    }

    fn visit_arm(&mut self, a: &'tcx hir::Arm<'tcx>) {
        self.add_id(a.hir_id);
        intravisit::walk_arm(self, a);
    }

    fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
        self.add_id(trait_item.hir_id());
        intravisit::walk_trait_item(self, trait_item);
    }

    fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
        self.add_id(impl_item.hir_id());
        intravisit::walk_impl_item(self, impl_item);
    }
}

pub struct LintLevelsBuilder<'s, P> {
    sess: &'s Session,
    features: &'s Features,
    provider: P,
    lint_added_lints: bool,
    store: &'s LintStore,
    registered_tools: &'s RegisteredTools,
}

pub(crate) struct BuilderPush {
    prev: LintStackIndex,
}

impl<'s> LintLevelsBuilder<'s, TopDown> {
    pub(crate) fn new(
        sess: &'s Session,
        features: &'s Features,
        lint_added_lints: bool,
        store: &'s LintStore,
        registered_tools: &'s RegisteredTools,
    ) -> Self {
        let mut builder = LintLevelsBuilder {
            sess,
            features,
            provider: TopDown { sets: LintLevelSets::new(), cur: COMMAND_LINE },
            lint_added_lints,
            store,
            registered_tools,
        };
        builder.process_command_line();
        assert_eq!(builder.provider.sets.list.len(), 1);
        builder
    }

    pub fn crate_root(
        sess: &'s Session,
        features: &'s Features,
        lint_added_lints: bool,
        store: &'s LintStore,
        registered_tools: &'s RegisteredTools,
        crate_attrs: &[ast::Attribute],
    ) -> Self {
        let mut builder = Self::new(sess, features, lint_added_lints, store, registered_tools);
        let parsed_crate_attrs = AttributeParser::parse_limited_all_filtered(
            sess,
            crate_attrs,
            ALLOW_LISTED_ATTRS,
            Target::Crate,
            DUMMY_SP,
            DUMMY_NODE_ID,
            Some(features),
            rustc_attr_parsing::ShouldEmit::Nothing,
            registered_tools,
        );

        builder.add(&parsed_crate_attrs, None);
        builder
    }

    fn process_command_line(&mut self) {
        self.provider.cur = self
            .provider
            .sets
            .list
            .push(LintSet { specs: FxIndexMap::default(), parent: COMMAND_LINE });
        self.add_command_line();
    }

    /// Pushes a list of AST lint attributes onto this context.
    ///
    /// This function will return a `BuilderPush` object which should be passed
    /// to `pop` when this scope for the attributes provided is exited.
    ///
    /// This function will perform a number of tasks:
    ///
    /// * It'll validate all lint-related attributes in `attrs`
    /// * It'll mark all lint-related attributes as used
    /// * Lint levels will be updated based on the attributes provided
    /// * Lint attributes are validated, e.g., a `#[forbid]` can't be switched to
    ///   `#[allow]`
    ///
    /// Don't forget to call `pop`!
    pub(crate) fn push(
        &mut self,
        attrs: &[ast::Attribute],
        node_id: NodeId,
        target_span: Span,
    ) -> BuilderPush {
        let prev = self.provider.cur;
        self.provider.cur =
            self.provider.sets.list.push(LintSet { specs: FxIndexMap::default(), parent: prev });
        if !attrs.is_empty() {
            let attrs = AttributeParser::parse_limited_all_filtered(
                self.sess,
                attrs,
                ALLOW_LISTED_ATTRS,
                Target::Fn,
                target_span,
                node_id,
                Some(self.features),
                rustc_attr_parsing::ShouldEmit::Nothing,
                self.registered_tools,
            );

            self.add(&attrs, None);

            if self.provider.current_specs().is_empty() {
                self.provider.sets.list.pop();
                self.provider.cur = prev;
            }
        }

        BuilderPush { prev }
    }

    /// Called after `push` when the scope of a set of attributes are exited.
    pub(crate) fn pop(&mut self, push: BuilderPush) {
        self.provider.cur = push.prev;
        std::mem::forget(push);
    }
}

#[cfg(debug_assertions)]
impl Drop for BuilderPush {
    fn drop(&mut self) {
        panic!("Found a `push` without a `pop`.");
    }
}

impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
    pub(crate) fn sess(&self) -> &Session {
        self.sess
    }

    pub(crate) fn features(&self) -> &Features {
        self.features
    }

    fn current_specs(&self) -> &FxIndexMap<LintId, LevelAndSource> {
        self.provider.current_specs()
    }

    fn insert(&mut self, id: LintId, lvl: LevelAndSource) {
        self.provider.insert(id, lvl)
    }

    fn add_command_line(&mut self) {
        for &(ref lint_name, level) in &self.sess.opts.lint_opts {
            // Checks the validity of lint names derived from the command line.
            let (tool_name, lint_name_only) = parse_lint_and_tool_name(lint_name);
            if lint_name_only == crate::WARNINGS.name_lower() && matches!(level, Level::ForceWarn) {
                self.sess
                    .dcx()
                    .emit_err(UnsupportedGroup { lint_group: crate::WARNINGS.name_lower() });
            }
            match self.store.check_lint_name(lint_name_only, tool_name, self.registered_tools) {
                CheckLintNameResult::Renamed(replace) => {
                    let name = lint_name.as_str();
                    let suggestion = RenamedLintSuggestion::WithoutSpan { replace };
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint =
                        RenamedLintFromCommandLine { name, replace, suggestion, requested_level };
                    self.emit_lint(RENAMED_AND_REMOVED_LINTS, lint);
                }
                CheckLintNameResult::Removed(ref reason) => {
                    let name = lint_name.as_str();
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint = RemovedLintFromCommandLine { name, reason, requested_level };
                    self.emit_lint(RENAMED_AND_REMOVED_LINTS, lint);
                }
                CheckLintNameResult::NoLint(suggestion) => {
                    let name = lint_name.clone();
                    let suggestion = suggestion.map(|(replace, from_rustc)| {
                        UnknownLintSuggestion::WithoutSpan { replace, from_rustc }
                    });
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint = UnknownLintFromCommandLine { name, suggestion, requested_level };
                    self.emit_lint(UNKNOWN_LINTS, lint);
                }
                CheckLintNameResult::Tool(_, Some(ref replace)) => {
                    let name = lint_name.clone();
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint = DeprecatedLintNameFromCommandLine { name, replace, requested_level };
                    self.emit_lint(RENAMED_AND_REMOVED_LINTS, lint);
                }
                CheckLintNameResult::NoTool => {
                    self.sess.dcx().emit_err(CheckNameUnknownTool {
                        tool_name: tool_name.unwrap(),
                        sub: RequestedLevel { level, lint_name },
                    });
                }
                _ => {}
            };

            let lint_flag_val = Symbol::intern(lint_name);

            let Some(ids) = self.store.find_lints(lint_name) else {
                // errors already handled above
                continue;
            };
            for &id in ids {
                // ForceWarn and Forbid cannot be overridden
                if let Some(LevelAndSource { level: Level::ForceWarn | Level::Forbid, .. }) =
                    self.current_specs().get(&id)
                {
                    continue;
                }

                if self.check_gated_lint(id, DUMMY_SP, true) {
                    let src = LintLevelSource::CommandLine(lint_flag_val, level);
                    self.insert(id, LevelAndSource { level, lint_id: None, src });
                }
            }
        }
    }

    /// Attempts to insert the `id` to `level_src` map entry. If unsuccessful
    /// (e.g. if a forbid was already inserted on the same scope), then emits a
    /// diagnostic with no change to `specs`.
    fn insert_spec(&mut self, id: LintId, LevelAndSource { level, lint_id, src }: LevelAndSource) {
        let LevelAndSource { level: old_level, src: old_src, .. } =
            self.provider.get_lint_level(id.lint, self.sess);

        // Setting to a non-forbid level is an error if the lint previously had
        // a forbid level. Note that this is not necessarily true even with a
        // `#[forbid(..)]` attribute present, as that is overridden by `--cap-lints`.
        //
        // This means that this only errors if we're truly lowering the lint
        // level from forbid.
        if self.lint_added_lints && level == Level::Deny && old_level == Level::Forbid {
            // Having a deny inside a forbid is fine and is ignored, so we skip this check.
            return;
        } else if self.lint_added_lints && level != Level::Forbid && old_level == Level::Forbid {
            // Backwards compatibility check:
            //
            // We used to not consider `forbid(lint_group)`
            // as preventing `allow(lint)` for some lint `lint` in
            // `lint_group`. For now, issue a future-compatibility
            // warning for this case.
            let id_name = id.lint.name_lower();
            let fcw_warning = match old_src {
                LintLevelSource::Default => false,
                LintLevelSource::Node { name, .. } => self.store.is_lint_group(name),
                LintLevelSource::CommandLine(symbol, _) => self.store.is_lint_group(symbol),
            };
            debug!(
                "fcw_warning={:?}, specs.get(&id) = {:?}, old_src={:?}, id_name={:?}",
                fcw_warning,
                self.current_specs(),
                old_src,
                id_name
            );
            let sub = match old_src {
                LintLevelSource::Default => {
                    OverruledAttributeSub::DefaultSource { id: id.to_string() }
                }
                LintLevelSource::Node { span, reason, .. } => {
                    OverruledAttributeSub::NodeSource { span, reason }
                }
                LintLevelSource::CommandLine(name, _) => {
                    OverruledAttributeSub::CommandLineSource { id: name }
                }
            };
            if !fcw_warning {
                self.sess.dcx().emit_err(OverruledAttribute {
                    span: src.span(),
                    overruled: src.span(),
                    lint_level: level.as_str(),
                    lint_source: src.name(),
                    sub,
                });
            } else {
                self.emit_span_lint(
                    FORBIDDEN_LINT_GROUPS,
                    src.span().into(),
                    OverruledAttributeLint {
                        overruled: src.span(),
                        lint_level: level.as_str(),
                        lint_source: src.name(),
                        sub,
                    },
                );
            }

            // Retain the forbid lint level, unless we are
            // issuing a FCW. In the FCW case, we want to
            // respect the new setting.
            if !fcw_warning {
                return;
            }
        }

        // The lint `unfulfilled_lint_expectations` can't be expected, as it would suppress itself.
        // Handling expectations of this lint would add additional complexity with little to no
        // benefit. The expect level for this lint will therefore be ignored.
        if let Level::Expect = level
            && id == LintId::of(UNFULFILLED_LINT_EXPECTATIONS)
        {
            return;
        }

        match (old_level, level) {
            // If the new level is an expectation store it in `ForceWarn`
            (Level::ForceWarn, Level::Expect) => {
                self.insert(id, LevelAndSource { level: Level::ForceWarn, lint_id, src: old_src })
            }
            // Keep `ForceWarn` level but drop the expectation
            (Level::ForceWarn, _) => self.insert(
                id,
                LevelAndSource { level: Level::ForceWarn, lint_id: None, src: old_src },
            ),
            // Set the lint level as normal
            _ => self.insert(id, LevelAndSource { level, lint_id, src }),
        };
    }

    fn simple_add(
        &mut self,
        level: Level,
        lint: &LintInstance,
        reason: Option<Symbol>,
        expect_lint_id: Option<LintExpectationId>,
    ) {
        // If this function returns none, it means the attribute parser has already emitted appropriate errors

        let src =
            LintLevelSource::Node { name: lint.original_lint_name(), span: lint.span(), reason };

        let id = match self.store.get_lint_by_name(lint.full_lint().as_str()) {
            Some(TargetLint::Id(id)) => id,
            None | Some(_) => bug!(
                "guaranteed to find id due to previous parsing, happened while parsing {:?}",
                lint,
            ),
        };

        if self.check_gated_lint(*id, lint.span(), false) {
            self.insert_spec(*id, LevelAndSource { level, lint_id: expect_lint_id, src });
        }
    }

    fn add(&mut self, attrs: &[hir::Attribute], source_hir_id: Option<HirId>) {
        if find_attr!(attrs, AutomaticallyDerived(..)) {
            self.insert(
                LintId::of(SINGLE_USE_LIFETIMES),
                LevelAndSource {
                    level: Level::Allow,
                    lint_id: None,
                    src: LintLevelSource::Default,
                },
            );
        }
        // `#[doc(hidden)]` disables missing_docs check.
        if find_attr!(attrs, Doc(d) if d.hidden.is_some()) {
            self.insert(
                LintId::of(MISSING_DOCS),
                LevelAndSource {
                    level: Level::Allow,
                    lint_id: None,
                    src: LintLevelSource::Default,
                },
            );
        }

        let Some(attrs) = find_attr!(attrs, LintAttributes(sub_attrs) => sub_attrs.into_iter())
        else {
            return;
        };

        for (attr_index, LintAttribute { reason, lint_instances, attr_id, kind, .. }) in
            attrs.enumerate()
        {
            let attr_id = attr_id.attr_id;
            let level = match kind {
                LintAttributeKind::Allow => Level::Allow,
                LintAttributeKind::Deny => Level::Deny,
                LintAttributeKind::Forbid => Level::Forbid,
                LintAttributeKind::Warn => Level::Warn,
                LintAttributeKind::Expect => {
                    for lint in lint_instances {
                        let lint_index = lint.lint_index().try_into().unwrap();
                        let attr_index = attr_index.try_into().unwrap();
                        let expectation_id = match source_hir_id {
                            None => LintExpectationId::Unstable { attr_id, lint_index },
                            Some(hir_id) => LintExpectationId::Stable {
                                hir_id,
                                attr_id,
                                lint_index,
                                attr_index,
                            },
                        };

                        self.simple_add(Level::Expect, lint, *reason, Some(expectation_id));

                        let is_unfulfilled_lint_expectations =
                            lint.lint_name().as_str() == UNFULFILLED_LINT_EXPECTATIONS.name_lower();
                        self.provider.push_expectation(
                            expectation_id,
                            LintExpectation::new(
                                *reason,
                                lint.span(),
                                is_unfulfilled_lint_expectations,
                                lint.tool_name(),
                            ),
                        );
                    }

                    continue;
                }
            };
            for lint in lint_instances {
                self.simple_add(level, lint, *reason, None);
            }
        }
    }

    /// Checks if the lint is gated on a feature that is not enabled.
    ///
    /// Returns `true` if the lint's feature is enabled.
    #[track_caller]
    fn check_gated_lint(&self, lint_id: LintId, span: Span, lint_from_cli: bool) -> bool {
        let feature = if let Some(feature) = lint_id.lint.feature_gate
            && !self.features.enabled(feature)
            && !span.allows_unstable(feature)
        {
            // Lint is behind a feature that is not enabled; eventually return false.
            feature
        } else {
            // Lint is ungated or its feature is enabled; exit early.
            return true;
        };

        struct UnknownLint<'a> {
            sess: &'a Session,
            lint_id: LintId,
            feature: Symbol,
            lint_from_cli: bool,
        }

        impl<'a, 'b> Diagnostic<'a, ()> for UnknownLint<'b> {
            fn into_diag(
                self,
                dcx: DiagCtxtHandle<'a>,
                level: rustc_errors::Level,
            ) -> Diag<'a, ()> {
                let Self { sess, lint_id, feature, lint_from_cli } = self;
                let mut lint = Diag::new(dcx, level, msg!("unknown lint: `{$name}`"))
                    .with_arg("name", lint_id.lint.name_lower())
                    .with_note(msg!("the `{$name}` lint is unstable"));
                rustc_session::parse::add_feature_diagnostics_for_issue(
                    &mut lint,
                    sess,
                    feature,
                    GateIssue::Language,
                    lint_from_cli,
                    None,
                );
                lint
            }
        }

        if self.lint_added_lints {
            let lint = builtin::UNKNOWN_LINTS;
            let level = self.lint_level(builtin::UNKNOWN_LINTS);
            emit_lint_base(
                self.sess,
                lint,
                level,
                Some(span.into()),
                UnknownLint { sess: &self.sess, lint_id, feature, lint_from_cli },
            );
        }

        false
    }

    /// Find the lint level for a lint.
    pub fn lint_level(&self, lint: &'static Lint) -> LevelAndSource {
        self.provider.get_lint_level(lint, self.sess)
    }

    /// Used to emit a lint-related diagnostic based on the current state of
    /// this lint context.
    #[track_caller]
    pub(crate) fn opt_span_lint(
        &self,
        lint: &'static Lint,
        span: Option<MultiSpan>,
        decorator: impl for<'a> Diagnostic<'a, ()>,
    ) {
        let level = self.lint_level(lint);
        emit_lint_base(self.sess, lint, level, span, decorator)
    }

    #[track_caller]
    pub fn emit_span_lint(
        &self,
        lint: &'static Lint,
        span: MultiSpan,
        decorator: impl for<'a> Diagnostic<'a, ()>,
    ) {
        let level = self.lint_level(lint);
        emit_lint_base(self.sess, lint, level, Some(span), decorator);
    }

    #[track_caller]
    pub fn emit_lint(&self, lint: &'static Lint, decorator: impl for<'a> Diagnostic<'a, ()>) {
        let level = self.lint_level(lint);
        emit_lint_base(self.sess, lint, level, None, decorator);
    }
}

pub(crate) fn provide(providers: &mut Providers) {
    *providers = Providers { shallow_lint_levels_on, lints_that_dont_need_to_run, ..*providers };
}

pub(crate) fn parse_lint_and_tool_name(lint_name: &str) -> (Option<Symbol>, &str) {
    match lint_name.split_once("::") {
        Some((tool_name, lint_name)) => {
            let tool_name = Symbol::intern(tool_name);

            (Some(tool_name), lint_name)
        }
        None => (None, lint_name),
    }
}