rustc_lint/

levels.rs

use std::fmt::Debug;

use rustc_ast as ast;
use rustc_ast::CRATE_NODE_ID;
use rustc_attr_ir::lint::{LintCheck, LintCheckKind};
use rustc_attr_ir::target::{AstTarget, Target};
use rustc_attr_ir::{Attribute, DocAttribute, find_attr};
use rustc_attr_parsing::{AttributeParser, Recovery, ShouldEmit};
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 as hir;
use rustc_hir::HirId;
use rustc_hir::intravisit::{self, Visitor};
use rustc_index::IndexVec;
use rustc_lint_defs::builtin::{
    self, FORBIDDEN_LINT_GROUPS, RENAMED_AND_REMOVED_LINTS, SINGLE_USE_LIFETIMES,
    UNFULFILLED_LINT_EXPECTATIONS, UNKNOWN_LINTS, UNUSED_ATTRIBUTES,
};
use rustc_lint_defs::{
    Level, Lint, LintExpectationId, LintId, StableLintExpectationId, UnstableLintExpectationId,
};
use rustc_middle::hir::nested_filter;
use rustc_middle::lint::{
    LevelSpec, LintExpectation, LintLevelSource, ShallowLintLevelMap, StableLevelSpec,
    UnstableLevelSpec, emit_lint_base, reveal_actual_level_spec,
};
use rustc_middle::query::Providers;
use rustc_middle::ty::{RegisteredTools, TyCtxt};
use rustc_session::Session;
use rustc_span::def_id::CRATE_MOD_ID;
use rustc_span::{AttrId, DUMMY_SP, Span, Symbol, sym};
use rustc_structures::LintName;
use tracing::{debug, instrument};

use crate::builtin::MISSING_DOCS;
use crate::context::{CheckLintNameResult, LintStore};
use crate::diagnostics::{
    CheckNameUnknownTool, DeprecatedLintName, DeprecatedLintNameFromCommandLine,
    IgnoredUnlessCrateSpecified, OverruledAttribute, OverruledAttributeLint, OverruledAttributeSub,
    RemovedLint, RemovedLintFromCommandLine, RenamedLint, RenamedLintFromCommandLine,
    RenamedLintSuggestion, RequestedLevel, UnknownLint, UnknownLintFromCommandLine,
    UnknownLintSuggestion, UnknownToolInScopedLint, UnsupportedGroup,
};
use crate::late::unerased_lint_store;

/// 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 {
    specs: FxIndexMap<LintId, UnstableLevelSpec>,
    parent: LintStackIndex,
}

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

    fn get_lint_level_spec(
        &self,
        lint: &'static Lint,
        idx: LintStackIndex,
        aux: Option<&FxIndexMap<LintId, UnstableLevelSpec>>,
        sess: &Session,
    ) -> UnstableLevelSpec {
        reveal_actual_level_spec(sess, LintId::of(lint), |id| {
            self.raw_lint_level_spec(id, idx, aux)
        })
    }

    fn raw_lint_level_spec(
        &self,
        id: LintId,
        mut idx: LintStackIndex,
        aux: Option<&FxIndexMap<LintId, UnstableLevelSpec>>,
    ) -> Option<UnstableLevelSpec> {
        if let Some(specs) = aux
            && let Some(level_spec) = specs.get(&id)
        {
            return Some(*level_spec);
        }

        loop {
            let LintSet { ref specs, parent } = self.list[idx];
            if let Some(level_spec) = specs.get(&id) {
                return Some(*level_spec);
            }
            if idx == COMMAND_LINE {
                return None;
            }
            idx = parent;
        }
    }
}

fn skippable_lints(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 skippable: 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 level_spec =
                root_map.lint_level_spec_at_node(tcx, LintId::of(lint), hir::CRATE_HIR_ID);
            // Only include lints that are allowed at crate root or by default.
            level_spec.is_allow()
                || (matches!(level_spec.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_spec) in specs.iter() {
                if !level_spec.is_allow() {
                    skippable.remove(lint);
                }
            }
        }
    }

    skippable.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_lint_tools: tcx.registered_lint_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, CRATE_MOD_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 {
    type LintExpectationId: Copy + Debug + Into<LintExpectationId>;

    fn current_specs(&self) -> &FxIndexMap<LintId, LevelSpec<Self::LintExpectationId>>;

    fn insert(&mut self, id: LintId, level_spec: LevelSpec<Self::LintExpectationId>);

    fn get_lint_level_spec(
        &self,
        lint: &'static Lint,
        sess: &Session,
    ) -> LevelSpec<Self::LintExpectationId>;

    fn push_expectation(&mut self, id: Self::LintExpectationId, expectation: LintExpectation);

    fn mk_lint_expectation_id(&self, attr_id: AttrId, lint_index: u16) -> Self::LintExpectationId;
}

impl LintLevelsProvider for TopDown {
    type LintExpectationId = UnstableLintExpectationId;

    fn current_specs(&self) -> &FxIndexMap<LintId, UnstableLevelSpec> {
        &self.sets.list[self.cur].specs
    }

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

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

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

    fn mk_lint_expectation_id(&self, attr_id: AttrId, lint_index: u16) -> Self::LintExpectationId {
        UnstableLintExpectationId { attr_id, lint_index }
    }
}

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

impl LintLevelsProvider for LintLevelQueryMap<'_> {
    type LintExpectationId = StableLintExpectationId;

    fn current_specs(&self) -> &FxIndexMap<LintId, StableLevelSpec> {
        self.specs.specs.get(&self.cur.local_id).unwrap_or(&self.empty)
    }

    fn insert(&mut self, id: LintId, level_spec: StableLevelSpec) {
        self.specs.specs.get_mut_or_insert_default(self.cur.local_id).insert(id, level_spec);
    }

    fn get_lint_level_spec(&self, lint: &'static Lint, _: &Session) -> StableLevelSpec {
        self.specs.lint_level_spec_at_node(self.tcx, LintId::of(lint), self.cur)
    }

    fn push_expectation(&mut self, id: Self::LintExpectationId, expectation: LintExpectation) {
        self.specs.expectations.push((id, expectation))
    }

    fn mk_lint_expectation_id(&self, _attr_id: AttrId, lint_index: u16) -> Self::LintExpectationId {
        StableLintExpectationId { hir_id: self.cur, lint_index }
    }
}

impl<'tcx> LintLevelsBuilder<'_, LintLevelQueryMap<'tcx>> {
    fn add_id(&mut self, hir_id: HirId) {
        self.provider.cur = hir_id;
        self.add_hir(self.provider.attrs.get(hir_id.local_id), hir_id == hir::CRATE_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_lint_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_lint_tools: &'s RegisteredTools,
    ) -> Self {
        let mut builder = LintLevelsBuilder {
            sess,
            features,
            provider: TopDown { sets: LintLevelSets::new(), cur: COMMAND_LINE },
            lint_added_lints,
            store,
            registered_lint_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_lint_tools: &'s RegisteredTools,
        crate_attrs: &[ast::Attribute],
    ) -> Self {
        let mut builder = Self::new(sess, features, lint_added_lints, store, registered_lint_tools);
        builder.add_ast(crate_attrs, true);
        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], is_crate_node: bool) -> BuilderPush {
        let prev = self.provider.cur;
        self.provider.cur =
            self.provider.sets.list.push(LintSet { specs: FxIndexMap::default(), parent: prev });

        self.add_ast(attrs, is_crate_node);

        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>
where
    LevelSpec<P::LintExpectationId>: Into<LevelSpec>,
{
    pub(crate) fn sess(&self) -> &Session {
        self.sess
    }

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

    fn add_command_line(&mut self) {
        for &(ref lint_name, level) in &self.sess.opts.lint_opts {
            let lint_name = LintName::from_str(lint_name);
            // Checks the validity of lint names derived from the command line.
            if lint_name.is(sym::warnings) && matches!(level, Level::ForceWarn) {
                self.sess
                    .dcx()
                    .emit_err(UnsupportedGroup { lint_group: crate::WARNINGS.name_lower() });
            }

            match self.store.check_lint_name(lint_name, self.registered_lint_tools) {
                CheckLintNameResult::Renamed(replacement) => {
                    let suggestion = RenamedLintSuggestion::WithoutSpan { replacement };
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint = RenamedLintFromCommandLine {
                        lint_name,
                        replacement,
                        suggestion,
                        requested_level,
                    };
                    self.emit_lint(RENAMED_AND_REMOVED_LINTS, lint);
                }
                CheckLintNameResult::Removed(ref reason) => {
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint = RemovedLintFromCommandLine { lint_name, reason, requested_level };
                    self.emit_lint(RENAMED_AND_REMOVED_LINTS, lint);
                }
                CheckLintNameResult::NoLint(suggestion) => {
                    let suggestion = suggestion.map(|(replacement, from_rustc)| {
                        UnknownLintSuggestion::WithoutSpan { replacement, from_rustc }
                    });
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint =
                        UnknownLintFromCommandLine { lint_name, suggestion, requested_level };
                    self.emit_lint(UNKNOWN_LINTS, lint);
                }
                CheckLintNameResult::Tool(_, Some(replacement)) => {
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint = DeprecatedLintNameFromCommandLine {
                        lint_name,
                        replacement,
                        requested_level,
                    };
                    self.emit_lint(RENAMED_AND_REMOVED_LINTS, lint);
                }
                CheckLintNameResult::NoTool(tool_name) => {
                    self.sess.dcx().emit_err(CheckNameUnknownTool {
                        tool_name,
                        sub: RequestedLevel { level, 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(level_spec) = self.provider.current_specs().get(&id)
                    && matches!(level_spec.level(), Level::ForceWarn | Level::Forbid)
                {
                    continue;
                }

                if self.check_gated_lint(id, DUMMY_SP, true) {
                    let src = LintLevelSource::CommandLine(lint_name, level);
                    self.provider.insert(id, LevelSpec::new(level, None, src));
                }
            }
        }
    }

    /// Attempts to insert the `id` to `LevelSpec` 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, level_spec: LevelSpec<P::LintExpectationId>) {
        let level = level_spec.level();
        let lint_id = level_spec.lint_id();
        let src = level_spec.src;

        let old_level_spec = self.provider.get_lint_level_spec(id.lint, self.sess);
        let old_level = old_level_spec.level();
        let old_src = old_level_spec.src;

        // 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 fcw_warning = match old_src {
                LintLevelSource::Default => false,
                LintLevelSource::Node { name, .. } => self.store.is_lint_group(name),
                LintLevelSource::CommandLine(name, _) => self.store.is_lint_group(name),
            };
            debug!(
                "fcw_warning={:?}, specs.get(&id) = {:?}, old_src={:?}, id_name={:?}",
                fcw_warning,
                self.provider.current_specs(),
                old_src,
                id.lint.name_lower(),
            );
            let sub = match old_src {
                LintLevelSource::Default => {
                    OverruledAttributeSub::DefaultSource { id: id.to_string() }
                }
                LintLevelSource::Node { span, reason, .. } => {
                    OverruledAttributeSub::NodeSource { span, reason }
                }
                LintLevelSource::CommandLine(lint_name, _) => {
                    OverruledAttributeSub::CommandLineSource { forbidden_lint_name: lint_name }
                }
            };
            if !fcw_warning {
                self.sess.dcx().emit_err(OverruledAttribute {
                    span: src.span(),
                    overruled: src.span(),
                    lint_level: level.as_str(),
                    lint_name: src.name(),
                    sub,
                });
            } else {
                self.emit_span_lint(
                    FORBIDDEN_LINT_GROUPS,
                    src.span().into(),
                    OverruledAttributeLint {
                        overruled: src.span(),
                        lint_level: level.as_str(),
                        lint_name: 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.provider.insert(id, LevelSpec::new(Level::ForceWarn, lint_id, old_src))
            }
            // Keep `ForceWarn` level but drop the expectation
            (Level::ForceWarn, _) => {
                self.provider.insert(id, LevelSpec::new(Level::ForceWarn, None, old_src))
            }
            // Set the lint level as normal
            _ => self.provider.insert(id, LevelSpec::new(level, lint_id, src)),
        };
    }

    fn add_ast(&mut self, attrs: &[rustc_ast::Attribute], is_crate_node: bool) {
        if attrs.is_empty() {
            return;
        }
        for attr in attrs {
            // `SINGLE_USE_LIFETIMES` is an AST lint so we only insert this here
            if attr.has_name(sym::automatically_derived) {
                self.provider.insert(
                    LintId::of(SINGLE_USE_LIFETIMES),
                    LevelSpec::new(Level::Allow, None, LintLevelSource::Default),
                );
            }
        }
        let parsed = AttributeParser::parse_limited_all(
            self.sess,
            attrs,
            Some(&|attr| {
                // This is ...complicated. Sometimes we need to parse lint check
                // attributes pre-expansion, but of course things are allowed to
                // be invalid if they're removed by a macro/cfg attribute before
                // we do attribute parsing, which happens (mostly) post-expansion.
                //
                // Unfortunately we're somewhat inconsistent - sometimes we just
                // give up and sometimes we error. Take for example:
                //
                // #[expect] // OK
                // #[expect[wut]] // OK
                // #[expect(expect)] // OK
                // #[expect(expect(expect))] //~ ERROR malformed lint attribute input
                // #[deny(({!}))] // OK
                // #[expect[helix::<ub>]] // OK
                // #[cfg(false)]
                // const _: () = ();
                //
                // FIXME: just allow everything?
                (attr.path_matches(&[sym::allow])
                    || attr.path_matches(&[sym::warn])
                    || attr.path_matches(&[sym::deny])
                    || attr.path_matches(&[sym::forbid])
                    || attr.path_matches(&[sym::expect]))
                    && attr.meta_item_list().is_some()
            }),
            AstTarget::None(Target::Crate),
            DUMMY_SP,
            CRATE_NODE_ID,
            Some(self.features),
            ShouldEmit::ErrorsAndLints { recovery: Recovery::Allowed },
            Some(self.registered_lint_tools),
        );
        self.add_hir_inner(&parsed, is_crate_node)
    }

    fn add_hir(&mut self, attrs: &[Attribute], is_crate_node: bool) {
        if attrs.is_empty() {
            return;
        }
        // `MISSING_DOCS` is a HIR lint so we only insert this here
        if find_attr!(attrs, Doc(DocAttribute { hidden: Some(_), .. })) {
            self.provider.insert(
                LintId::of(MISSING_DOCS),
                LevelSpec::new(Level::Allow, None, LintLevelSource::Default),
            );
        }
        self.add_hir_inner(attrs, is_crate_node)
    }

    fn add_hir_inner(&mut self, attrs: &[Attribute], is_crate_node: bool) {
        let Some(lint_checks) = find_attr!(attrs, LintCheck(lints) => lints.clone()) else {
            return;
        };

        let sess = self.sess;

        // FIXME: consider performing these checks in attribute parsing instead
        for (lint_index, lint_check) in lint_checks.into_iter().enumerate() {
            let LintCheck { lint_name, kind, reason, attr_id, attr_span: _, lint_span, tool_span } =
                lint_check;
            let LintName { tool, name: _ } = lint_name;

            let level = match kind {
                LintCheckKind::Allow => Level::Allow,
                LintCheckKind::Warn => Level::Warn,
                LintCheckKind::Deny => Level::Deny,
                LintCheckKind::Forbid => Level::Forbid,
                LintCheckKind::Expect => Level::Expect,
            };

            // `Expect` is the only lint level with a `LintExpectationId` that can be created
            // from an attribute.
            let lint_id = (level == Level::Expect)
                .then(|| self.provider.mk_lint_expectation_id(attr_id.attr_id, lint_index as u16));

            let lint_result = self.store.check_lint_name(lint_name, self.registered_lint_tools);

            let (ids, name): (_, LintName) = match lint_result {
                CheckLintNameResult::Ok(ids) => (ids, lint_name),

                CheckLintNameResult::Tool(ids, new_lint_name) => {
                    let name = match new_lint_name {
                        None => lint_name,
                        Some(replacement) => {
                            self.emit_span_lint(
                                builtin::RENAMED_AND_REMOVED_LINTS,
                                lint_span.into(),
                                DeprecatedLintName {
                                    lint_name,
                                    suggestion: lint_span,
                                    replacement,
                                },
                            );
                            replacement
                        }
                    };
                    (ids, name)
                }

                CheckLintNameResult::MissingTool => {
                    // If `MissingTool` is returned, then either the lint does not
                    // exist in the tool or the code was not compiled with the tool and
                    // therefore the lint was never added to the `LintStore`. To detect
                    // this is the responsibility of the lint tool.
                    continue;
                }

                CheckLintNameResult::NoTool(tool_name) => {
                    sess.dcx().emit_err(UnknownToolInScopedLint {
                        span: Some(tool_span.unwrap()),
                        tool_name,
                        lint_name,
                        is_nightly_build: sess.is_nightly_build(),
                    });
                    continue;
                }

                CheckLintNameResult::Renamed(replacement) => {
                    if self.lint_added_lints {
                        let suggestion =
                            RenamedLintSuggestion::WithSpan { suggestion: lint_span, replacement };

                        self.emit_span_lint(
                            RENAMED_AND_REMOVED_LINTS,
                            lint_span.into(),
                            RenamedLint { name: lint_name, replacement, suggestion },
                        );
                    }

                    // If this lint was renamed, apply the new lint instead of ignoring the
                    // attribute. Ignore any errors or warnings that happen because the new
                    // name is inaccurate.
                    let replace_check =
                        self.store.check_lint_name(replacement, self.registered_lint_tools);
                    let (CheckLintNameResult::Ok(ids) | CheckLintNameResult::Tool(ids, _)) =
                        replace_check
                    else {
                        panic!("renamed lint does not exist: {replacement} :{replace_check:?}");
                    };

                    (ids, replacement)
                }

                CheckLintNameResult::Removed(ref reason) => {
                    if self.lint_added_lints {
                        self.emit_span_lint(
                            RENAMED_AND_REMOVED_LINTS,
                            lint_span.into(),
                            RemovedLint { name: lint_name, reason },
                        );
                    }
                    continue;
                }

                CheckLintNameResult::NoLint(suggestion) => {
                    if self.lint_added_lints {
                        let suggestion = suggestion.map(|(replacement, from_rustc)| {
                            UnknownLintSuggestion::WithSpan {
                                suggestion: lint_span,
                                replacement,
                                from_rustc,
                            }
                        });
                        self.emit_span_lint(
                            UNKNOWN_LINTS,
                            lint_span.into(),
                            UnknownLint { name: lint_name, suggestion },
                        );
                    }
                    continue;
                }
            };

            let src = LintLevelSource::Node { name, span: lint_span, reason };
            for &id in ids {
                if self.check_gated_lint(id, lint_span, false) {
                    self.insert_spec(id, LevelSpec::new(level, lint_id, src));
                }
            }

            // This checks for instances where the user writes
            // `#[expect(unfulfilled_lint_expectations)]` in that case we want to avoid
            // overriding the lint level but instead add an expectation that can't be
            // fulfilled. The lint message will include an explanation, that the
            // `unfulfilled_lint_expectations` lint can't be expected.
            if let (Level::Expect, Some(expect_id)) = (level, lint_id) {
                // The `unfulfilled_lint_expectations` lint is not part of any lint
                // groups. Therefore. we only need to check the slice if it contains a
                // single lint.
                let is_unfulfilled_lint_expectations = match ids {
                    [lint] => *lint == LintId::of(UNFULFILLED_LINT_EXPECTATIONS),
                    _ => false,
                };
                self.provider.push_expectation(
                    expect_id,
                    LintExpectation::new(reason, lint_span, is_unfulfilled_lint_expectations, tool),
                );
            }
        }

        if self.lint_added_lints && !is_crate_node {
            for (id, level_spec) in self.provider.current_specs().iter() {
                if !id.lint.crate_level_only {
                    continue;
                }

                let LintLevelSource::Node { name: lint_attr_name, span: lint_attr_span, .. } =
                    level_spec.src
                else {
                    continue;
                };

                self.emit_span_lint(
                    UNUSED_ATTRIBUTES,
                    lint_attr_span.into(),
                    IgnoredUnlessCrateSpecified {
                        level: level_spec.level().as_str(),
                        lint_name: lint_attr_name,
                    },
                );
                // don't set a separate error for every lint in the group
                break;
            }
        }
    }

    /// 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"));
                // `staged_api` is only intended for the standard library, so don't
                // suggest enabling it just to use this lint.
                if feature != sym::staged_api {
                    rustc_session::diagnostics::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_spec = self.lint_level_spec(builtin::UNKNOWN_LINTS);
            emit_lint_base(
                self.sess,
                lint,
                level_spec,
                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_spec(&self, lint: &'static Lint) -> LevelSpec<P::LintExpectationId> {
        self.provider.get_lint_level_spec(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_spec = self.lint_level_spec(lint);
        emit_lint_base(self.sess, lint, level_spec, span, decorator)
    }

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

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

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