rustc_passes/

check_attr.rs

// FIXME(jdonszelmann): should become rustc_attr_validation
//! This module implements some validity checks for attributes.
//! In particular it verifies that `#[inline]` and `#[repr]` attributes are
//! attached to items that actually support them and if there are
//! conflicts between multiple such attributes attached to the same
//! item.

use std::cell::Cell;
use std::collections::hash_map::Entry;
use std::slice;

use rustc_abi::{Align, ExternAbi, Size};
use rustc_ast::{AttrStyle, LitKind, MetaItemKind, ast};
use rustc_attr_parsing::{AttributeParser, Late};
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{DiagCtxtHandle, IntoDiagArg, MultiSpan, StashKey};
use rustc_feature::{
    ACCEPTED_LANG_FEATURES, AttributeDuplicates, AttributeType, BUILTIN_ATTRIBUTE_MAP,
    BuiltinAttribute,
};
use rustc_hir::attrs::{
    AttributeKind, DocAttribute, DocInline, EiiDecl, EiiImpl, InlineAttr, MirDialect, MirPhase,
    ReprAttr, SanitizerSet,
};
use rustc_hir::def::DefKind;
use rustc_hir::def_id::LocalModDefId;
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::{
    self as hir, Attribute, CRATE_HIR_ID, Constness, FnSig, ForeignItem, HirId, Item, ItemKind,
    MethodKind, PartialConstStability, Safety, Stability, StabilityLevel, Target, TraitItem,
    find_attr,
};
use rustc_macros::LintDiagnostic;
use rustc_middle::hir::nested_filter;
use rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault;
use rustc_middle::query::Providers;
use rustc_middle::traits::ObligationCause;
use rustc_middle::ty::error::{ExpectedFound, TypeError};
use rustc_middle::ty::{self, TyCtxt, TypingMode};
use rustc_middle::{bug, span_bug};
use rustc_session::config::CrateType;
use rustc_session::lint;
use rustc_session::lint::builtin::{
    CONFLICTING_REPR_HINTS, INVALID_DOC_ATTRIBUTES, MALFORMED_DIAGNOSTIC_ATTRIBUTES,
    MISPLACED_DIAGNOSTIC_ATTRIBUTES, UNUSED_ATTRIBUTES,
};
use rustc_session::parse::feature_err;
use rustc_span::edition::Edition;
use rustc_span::{BytePos, DUMMY_SP, Span, Symbol, sym};
use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
use rustc_trait_selection::infer::{TyCtxtInferExt, ValuePairs};
use rustc_trait_selection::traits::ObligationCtxt;
use tracing::debug;

use crate::{errors, fluent_generated as fluent};

#[derive(LintDiagnostic)]
#[diag(passes_diagnostic_diagnostic_on_unimplemented_only_for_traits)]
struct DiagnosticOnUnimplementedOnlyForTraits;

#[derive(LintDiagnostic)]
#[diag(passes_diagnostic_diagnostic_on_const_only_for_trait_impls)]
struct DiagnosticOnConstOnlyForTraitImpls {
    #[label]
    item_span: Span,
}

fn target_from_impl_item<'tcx>(tcx: TyCtxt<'tcx>, impl_item: &hir::ImplItem<'_>) -> Target {
    match impl_item.kind {
        hir::ImplItemKind::Const(..) => Target::AssocConst,
        hir::ImplItemKind::Fn(..) => {
            let parent_def_id = tcx.hir_get_parent_item(impl_item.hir_id()).def_id;
            let containing_item = tcx.hir_expect_item(parent_def_id);
            let containing_impl_is_for_trait = match &containing_item.kind {
                hir::ItemKind::Impl(impl_) => impl_.of_trait.is_some(),
                _ => bug!("parent of an ImplItem must be an Impl"),
            };
            if containing_impl_is_for_trait {
                Target::Method(MethodKind::Trait { body: true })
            } else {
                Target::Method(MethodKind::Inherent)
            }
        }
        hir::ImplItemKind::Type(..) => Target::AssocTy,
    }
}

#[derive(Clone, Copy)]
enum ItemLike<'tcx> {
    Item(&'tcx Item<'tcx>),
    ForeignItem,
}

#[derive(Copy, Clone)]
pub(crate) enum ProcMacroKind {
    FunctionLike,
    Derive,
    Attribute,
}

impl IntoDiagArg for ProcMacroKind {
    fn into_diag_arg(self, _: &mut Option<std::path::PathBuf>) -> rustc_errors::DiagArgValue {
        match self {
            ProcMacroKind::Attribute => "attribute proc macro",
            ProcMacroKind::Derive => "derive proc macro",
            ProcMacroKind::FunctionLike => "function-like proc macro",
        }
        .into_diag_arg(&mut None)
    }
}

struct CheckAttrVisitor<'tcx> {
    tcx: TyCtxt<'tcx>,

    // Whether or not this visitor should abort after finding errors
    abort: Cell<bool>,
}

impl<'tcx> CheckAttrVisitor<'tcx> {
    fn dcx(&self) -> DiagCtxtHandle<'tcx> {
        self.tcx.dcx()
    }

    /// Checks any attribute.
    fn check_attributes(
        &self,
        hir_id: HirId,
        span: Span,
        target: Target,
        item: Option<ItemLike<'_>>,
    ) {
        let mut seen = FxHashMap::default();
        let attrs = self.tcx.hir_attrs(hir_id);
        for attr in attrs {
            let mut style = None;
            match attr {
                Attribute::Parsed(AttributeKind::ProcMacro(_)) => {
                    self.check_proc_macro(hir_id, target, ProcMacroKind::FunctionLike)
                }
                Attribute::Parsed(AttributeKind::ProcMacroAttribute(_)) => {
                    self.check_proc_macro(hir_id, target, ProcMacroKind::Attribute);
                }
                Attribute::Parsed(AttributeKind::ProcMacroDerive { .. }) => {
                    self.check_proc_macro(hir_id, target, ProcMacroKind::Derive)
                }
                Attribute::Parsed(
                    AttributeKind::Stability {
                        span: attr_span,
                        stability: Stability { level, feature },
                    }
                    | AttributeKind::ConstStability {
                        span: attr_span,
                        stability: PartialConstStability { level, feature, .. },
                    },
                ) => self.check_stability(*attr_span, span, level, *feature),
                Attribute::Parsed(AttributeKind::Inline(InlineAttr::Force { .. }, ..)) => {} // handled separately below
                Attribute::Parsed(AttributeKind::Inline(kind, attr_span)) => {
                    self.check_inline(hir_id, *attr_span, kind, target)
                }
                Attribute::Parsed(AttributeKind::LoopMatch(attr_span)) => {
                    self.check_loop_match(hir_id, *attr_span, target)
                }
                Attribute::Parsed(AttributeKind::ConstContinue(attr_span)) => {
                    self.check_const_continue(hir_id, *attr_span, target)
                }
                Attribute::Parsed(AttributeKind::AllowInternalUnsafe(attr_span) | AttributeKind::AllowInternalUnstable(.., attr_span)) => {
                    self.check_macro_only_attr(*attr_span, span, target, attrs)
                }
                Attribute::Parsed(AttributeKind::AllowConstFnUnstable(_, first_span)) => {
                    self.check_rustc_allow_const_fn_unstable(hir_id, *first_span, span, target)
                }
                Attribute::Parsed(AttributeKind::Deprecation {span: attr_span, .. }) => {
                    self.check_deprecated(hir_id, *attr_span, target)
                }
                Attribute::Parsed(AttributeKind::TargetFeature{ attr_span, ..}) => {
                    self.check_target_feature(hir_id, *attr_span, target, attrs)
                }
                Attribute::Parsed(AttributeKind::RustcObjectLifetimeDefault) => {
                    self.check_object_lifetime_default(hir_id);
                }
                &Attribute::Parsed(AttributeKind::PubTransparent(attr_span)) => {
                    self.check_rustc_pub_transparent(attr_span, span, attrs)
                }
                Attribute::Parsed(AttributeKind::Align { align, span: attr_span }) => {
                    self.check_align(*align, *attr_span)
                }
                Attribute::Parsed(AttributeKind::Naked(..)) => {
                    self.check_naked(hir_id, target)
                }
                Attribute::Parsed(AttributeKind::TrackCaller(attr_span)) => {
                    self.check_track_caller(hir_id, *attr_span, attrs, target)
                }
                Attribute::Parsed(AttributeKind::NonExhaustive(attr_span)) => {
                    self.check_non_exhaustive(*attr_span, span, target, item)
                }
                &Attribute::Parsed(AttributeKind::FfiPure(attr_span)) => {
                    self.check_ffi_pure(attr_span, attrs)
                }
                Attribute::Parsed(AttributeKind::MayDangle(attr_span)) => {
                    self.check_may_dangle(hir_id, *attr_span)
                }
                &Attribute::Parsed(AttributeKind::CustomMir(dialect, phase, attr_span)) => {
                    self.check_custom_mir(dialect, phase, attr_span)
                }
                &Attribute::Parsed(AttributeKind::Sanitize { on_set, off_set, rtsan: _, span: attr_span}) => {
                    self.check_sanitize(attr_span, on_set | off_set, span, target);
                },
                Attribute::Parsed(AttributeKind::Link(_, attr_span)) => {
                    self.check_link(hir_id, *attr_span, span, target)
                },
                Attribute::Parsed(AttributeKind::MacroExport { span, .. }) => {
                    self.check_macro_export(hir_id, *span, target)
                },
                Attribute::Parsed(AttributeKind::Doc(attr)) => self.check_doc_attrs(attr, hir_id, target),
                Attribute::Parsed(AttributeKind::EiiImpls(impls)) => {
                     self.check_eii_impl(impls, target)
                },
                Attribute::Parsed(
                    AttributeKind::EiiExternTarget { .. }
                    | AttributeKind::EiiExternItem
                    | AttributeKind::BodyStability { .. }
                    | AttributeKind::ConstStabilityIndirect
                    | AttributeKind::MacroTransparency(_)
                    | AttributeKind::Pointee(..)
                    | AttributeKind::Dummy
                    | AttributeKind::RustcBuiltinMacro { .. }
                    | AttributeKind::Ignore { .. }
                    | AttributeKind::Path(..)
                    | AttributeKind::NoImplicitPrelude(..)
                    | AttributeKind::AutomaticallyDerived(..)
                    | AttributeKind::Marker(..)
                    | AttributeKind::SkipDuringMethodDispatch { .. }
                    | AttributeKind::Coinductive(..)
                    | AttributeKind::DenyExplicitImpl(..)
                    | AttributeKind::DoNotImplementViaObject(..)
                    | AttributeKind::SpecializationTrait(..)
                    | AttributeKind::UnsafeSpecializationMarker(..)
                    | AttributeKind::ParenSugar(..)
                    | AttributeKind::AllowIncoherentImpl(..)
                    | AttributeKind::Confusables { .. }
                    | AttributeKind::TypeConst{..}
                    // `#[doc]` is actually a lot more than just doc comments, so is checked below
                    | AttributeKind::DocComment {..}
                    // handled below this loop and elsewhere
                    | AttributeKind::Repr { .. }
                    | AttributeKind::Cold(..)
                    | AttributeKind::ExportName { .. }
                    | AttributeKind::Fundamental
                    | AttributeKind::Optimize(..)
                    | AttributeKind::LinkSection { .. }
                    | AttributeKind::MacroUse { .. }
                    | AttributeKind::MacroEscape( .. )
                    | AttributeKind::RustcLayoutScalarValidRangeStart(..)
                    | AttributeKind::RustcLayoutScalarValidRangeEnd(..)
                    | AttributeKind::RustcScalableVector { .. }
                    | AttributeKind::RustcSimdMonomorphizeLaneLimit(..)
                    | AttributeKind::RustcShouldNotBeCalledOnConstItems(..)
                    | AttributeKind::ExportStable
                    | AttributeKind::FfiConst(..)
                    | AttributeKind::UnstableFeatureBound(..)
                    | AttributeKind::AsPtr(..)
                    | AttributeKind::LinkName { .. }
                    | AttributeKind::LinkOrdinal { .. }
                    | AttributeKind::NoMangle(..)
                    | AttributeKind::Used { .. }
                    | AttributeKind::PassByValue (..)
                    | AttributeKind::StdInternalSymbol (..)
                    | AttributeKind::Coverage (..)
                    | AttributeKind::ShouldPanic { .. }
                    | AttributeKind::Coroutine(..)
                    | AttributeKind::Linkage(..)
                    | AttributeKind::MustUse { .. }
                    | AttributeKind::CrateName { .. }
                    | AttributeKind::RecursionLimit { .. }
                    | AttributeKind::MoveSizeLimit { .. }
                    | AttributeKind::TypeLengthLimit { .. }
                    | AttributeKind::PatternComplexityLimit { .. }
                    | AttributeKind::NoCore { .. }
                    | AttributeKind::NoStd { .. }
                    | AttributeKind::ObjcClass { .. }
                    | AttributeKind::ObjcSelector { .. }
                    | AttributeKind::RustcCoherenceIsCore(..)
                    | AttributeKind::DebuggerVisualizer(..)
                    | AttributeKind::RustcMain
                    | AttributeKind::RustcPassIndirectlyInNonRusticAbis(..)
                    | AttributeKind::PinV2(..)
                    | AttributeKind::WindowsSubsystem(..)
                ) => { /* do nothing  */ }
                Attribute::Unparsed(attr_item) => {
                    style = Some(attr_item.style);
                    match attr.path().as_slice() {
                        [sym::diagnostic, sym::do_not_recommend, ..] => {
                            self.check_do_not_recommend(attr.span(), hir_id, target, attr, item)
                        }
                        [sym::diagnostic, sym::on_unimplemented, ..] => {
                            self.check_diagnostic_on_unimplemented(attr.span(), hir_id, target)
                        }
                        [sym::diagnostic, sym::on_const, ..] => {
                            self.check_diagnostic_on_const(attr.span(), hir_id, target, item)
                        }
                        [sym::thread_local, ..] => self.check_thread_local(attr, span, target),
                        [sym::no_link, ..] => self.check_no_link(hir_id, attr, span, target),
                        [sym::rustc_no_implicit_autorefs, ..] => {
                            self.check_applied_to_fn_or_method(hir_id, attr.span(), span, target)
                        }
                        [sym::rustc_never_returns_null_ptr, ..] => {
                            self.check_applied_to_fn_or_method(hir_id, attr.span(), span, target)
                        }
                        [sym::rustc_legacy_const_generics, ..] => {
                            self.check_rustc_legacy_const_generics(hir_id, attr, span, target, item)
                        }
                        [sym::rustc_lint_query_instability, ..] => {
                            self.check_applied_to_fn_or_method(hir_id, attr.span(), span, target)
                        }
                        [sym::rustc_lint_untracked_query_information, ..] => {
                            self.check_applied_to_fn_or_method(hir_id, attr.span(), span, target)
                        }
                        [sym::rustc_lint_diagnostics, ..] => {
                            self.check_applied_to_fn_or_method(hir_id, attr.span(), span, target)
                        }
                        [sym::rustc_lint_opt_ty, ..] => self.check_rustc_lint_opt_ty(attr, span, target),
                        [sym::rustc_lint_opt_deny_field_access, ..] => {
                            self.check_rustc_lint_opt_deny_field_access(attr, span, target)
                        }
                        [sym::rustc_clean, ..]
                        | [sym::rustc_dirty, ..]
                        | [sym::rustc_if_this_changed, ..]
                        | [sym::rustc_then_this_would_need, ..] => self.check_rustc_dirty_clean(attr),
                        [sym::rustc_must_implement_one_of, ..] => self.check_must_be_applied_to_trait(attr.span(), span, target),
                        [sym::collapse_debuginfo, ..] => self.check_collapse_debuginfo(attr, span, target),
                        [sym::must_not_suspend, ..] => self.check_must_not_suspend(attr, span, target),
                        [sym::rustc_has_incoherent_inherent_impls, ..] => {
                            self.check_has_incoherent_inherent_impls(attr, span, target)
                        }
                        [sym::autodiff_forward, ..] | [sym::autodiff_reverse, ..] => {
                            self.check_autodiff(hir_id, attr, span, target)
                        }
                        [
                            // ok
                            sym::allow
                            | sym::expect
                            | sym::warn
                            | sym::deny
                            | sym::forbid
                            | sym::cfg
                            | sym::cfg_attr
                            | sym::cfg_trace
                            | sym::cfg_attr_trace
                            // need to be fixed
                            | sym::cfi_encoding // FIXME(cfi_encoding)
                            | sym::instruction_set // broken on stable!!!
                            | sym::patchable_function_entry // FIXME(patchable_function_entry)
                            | sym::deprecated_safe // FIXME(deprecated_safe)
                            // internal
                            | sym::prelude_import
                            | sym::panic_handler
                            | sym::lang
                            | sym::needs_allocator
                            | sym::default_lib_allocator,
                            ..
                        ] => {}
                        [name, rest@..] => {
                            match BUILTIN_ATTRIBUTE_MAP.get(name) {
                                // checked below
                                Some(BuiltinAttribute { type_: AttributeType::CrateLevel, .. }) => {}
                                Some(_) => {
                                    if rest.len() > 0 && AttributeParser::<Late>::is_parsed_attribute(slice::from_ref(name)) {
                                        // Check if we tried to use a builtin attribute as an attribute namespace, like `#[must_use::skip]`.
                                        // This check is here to solve https://github.com/rust-lang/rust/issues/137590
                                        // An error is already produced for this case elsewhere
                                        continue
                                    }

                                    // FIXME: differentiate between unstable and internal attributes just
                                    // like we do with features instead of just accepting `rustc_`
                                    // attributes by name. That should allow trimming the above list, too.
                                    if !name.as_str().starts_with("rustc_") {
                                        span_bug!(
                                            attr.span(),
                                            "builtin attribute {name:?} not handled by `CheckAttrVisitor`"
                                        )
                                    }
                                }
                                None => (),
                            }
                        }
                        [] => unreachable!(),
                    }
                }
            }

            if hir_id != CRATE_HIR_ID {
                match attr {
                    Attribute::Parsed(_) => { /* Already validated. */ }
                    Attribute::Unparsed(attr) => {
                        // FIXME(jdonszelmann): remove once all crate-level attrs are parsed and caught by
                        // the above
                        if let Some(BuiltinAttribute { type_: AttributeType::CrateLevel, .. }) =
                            attr.path
                                .segments
                                .first()
                                .and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name))
                        {
                            match attr.style {
                                ast::AttrStyle::Outer => {
                                    let attr_span = attr.span;
                                    let bang_position = self
                                        .tcx
                                        .sess
                                        .source_map()
                                        .span_until_char(attr_span, '[')
                                        .shrink_to_hi();

                                    self.tcx.emit_node_span_lint(
                                        UNUSED_ATTRIBUTES,
                                        hir_id,
                                        attr.span,
                                        errors::OuterCrateLevelAttr {
                                            suggestion: errors::OuterCrateLevelAttrSuggestion {
                                                bang_position,
                                            },
                                        },
                                    )
                                }
                                ast::AttrStyle::Inner => self.tcx.emit_node_span_lint(
                                    UNUSED_ATTRIBUTES,
                                    hir_id,
                                    attr.span,
                                    errors::InnerCrateLevelAttr,
                                ),
                            }
                        }
                    }
                }
            }

            if let Attribute::Unparsed(unparsed_attr) = attr
                && let Some(BuiltinAttribute { duplicates, .. }) =
                    attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name))
            {
                check_duplicates(
                    self.tcx,
                    unparsed_attr.span,
                    attr,
                    hir_id,
                    *duplicates,
                    &mut seen,
                );
            }

            self.check_unused_attribute(hir_id, attr, style)
        }

        self.check_repr(attrs, span, target, item, hir_id);
        self.check_rustc_force_inline(hir_id, attrs, target);
        self.check_mix_no_mangle_export(hir_id, attrs);
    }

    fn inline_attr_str_error_with_macro_def(&self, hir_id: HirId, attr_span: Span, sym: &str) {
        self.tcx.emit_node_span_lint(
            UNUSED_ATTRIBUTES,
            hir_id,
            attr_span,
            errors::IgnoredAttrWithMacro { sym },
        );
    }

    fn check_eii_impl(&self, impls: &[EiiImpl], target: Target) {
        for EiiImpl { span, inner_span, eii_macro, impl_marked_unsafe, is_default: _ } in impls {
            match target {
                Target::Fn => {}
                _ => {
                    self.dcx().emit_err(errors::EiiImplNotFunction { span: *span });
                }
            }

            if find_attr!(self.tcx.get_all_attrs(*eii_macro), AttributeKind::EiiExternTarget(EiiDecl { impl_unsafe, .. }) if *impl_unsafe)
                && !impl_marked_unsafe
            {
                self.dcx().emit_err(errors::EiiImplRequiresUnsafe {
                    span: *span,
                    name: self.tcx.item_name(*eii_macro),
                    suggestion: errors::EiiImplRequiresUnsafeSuggestion {
                        left: inner_span.shrink_to_lo(),
                        right: inner_span.shrink_to_hi(),
                    },
                });
            }
        }
    }

    /// Checks if `#[diagnostic::do_not_recommend]` is applied on a trait impl and that it has no
    /// arguments.
    fn check_do_not_recommend(
        &self,
        attr_span: Span,
        hir_id: HirId,
        target: Target,
        attr: &Attribute,
        item: Option<ItemLike<'_>>,
    ) {
        if !matches!(target, Target::Impl { .. })
            || matches!(
                item,
                Some(ItemLike::Item(hir::Item {  kind: hir::ItemKind::Impl(_impl),.. }))
                    if _impl.of_trait.is_none()
            )
        {
            self.tcx.emit_node_span_lint(
                MISPLACED_DIAGNOSTIC_ATTRIBUTES,
                hir_id,
                attr_span,
                errors::IncorrectDoNotRecommendLocation,
            );
        }
        if !attr.is_word() {
            self.tcx.emit_node_span_lint(
                MALFORMED_DIAGNOSTIC_ATTRIBUTES,
                hir_id,
                attr_span,
                errors::DoNotRecommendDoesNotExpectArgs,
            );
        }
    }

    /// Checks if `#[diagnostic::on_unimplemented]` is applied to a trait definition
    fn check_diagnostic_on_unimplemented(&self, attr_span: Span, hir_id: HirId, target: Target) {
        if !matches!(target, Target::Trait) {
            self.tcx.emit_node_span_lint(
                MISPLACED_DIAGNOSTIC_ATTRIBUTES,
                hir_id,
                attr_span,
                DiagnosticOnUnimplementedOnlyForTraits,
            );
        }
    }

    /// Checks if `#[diagnostic::on_const]` is applied to a trait impl
    fn check_diagnostic_on_const(
        &self,
        attr_span: Span,
        hir_id: HirId,
        target: Target,
        item: Option<ItemLike<'_>>,
    ) {
        if matches!(target, Target::Impl { of_trait: true }) {
            match item.unwrap() {
                ItemLike::Item(it) => match it.expect_impl().constness {
                    Constness::Const => {}
                    Constness::NotConst => return,
                },
                ItemLike::ForeignItem => {}
            }
        }
        let item_span = self.tcx.hir_span(hir_id);
        self.tcx.emit_node_span_lint(
            MISPLACED_DIAGNOSTIC_ATTRIBUTES,
            hir_id,
            attr_span,
            DiagnosticOnConstOnlyForTraitImpls { item_span },
        );
    }

    /// Checks if an `#[inline]` is applied to a function or a closure.
    fn check_inline(&self, hir_id: HirId, attr_span: Span, kind: &InlineAttr, target: Target) {
        match target {
            Target::Fn
            | Target::Closure
            | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => {
                // `#[inline]` is ignored if the symbol must be codegened upstream because it's exported.
                if let Some(did) = hir_id.as_owner()
                    && self.tcx.def_kind(did).has_codegen_attrs()
                    && kind != &InlineAttr::Never
                {
                    let attrs = self.tcx.codegen_fn_attrs(did);
                    // Not checking naked as `#[inline]` is forbidden for naked functions anyways.
                    if attrs.contains_extern_indicator() {
                        self.tcx.emit_node_span_lint(
                            UNUSED_ATTRIBUTES,
                            hir_id,
                            attr_span,
                            errors::InlineIgnoredForExported {},
                        );
                    }
                }
            }
            _ => {}
        }
    }

    /// Checks that the `#[sanitize(..)]` attribute is applied to a
    /// function/closure/method, or to an impl block or module.
    fn check_sanitize(
        &self,
        attr_span: Span,
        set: SanitizerSet,
        target_span: Span,
        target: Target,
    ) {
        let mut not_fn_impl_mod = None;
        let mut no_body = None;

        match target {
            Target::Fn
            | Target::Closure
            | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent)
            | Target::Impl { .. }
            | Target::Mod => return,
            Target::Static
                // if we mask out the address bits, i.e. *only* address was set,
                // we allow it
                if set & !(SanitizerSet::ADDRESS | SanitizerSet::KERNELADDRESS)
                    == SanitizerSet::empty() =>
            {
                return;
            }

            // These are "functions", but they aren't allowed because they don't
            // have a body, so the usual explanation would be confusing.
            Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
                no_body = Some(target_span);
            }

            _ => {
                not_fn_impl_mod = Some(target_span);
            }
        }

        self.dcx().emit_err(errors::SanitizeAttributeNotAllowed {
            attr_span,
            not_fn_impl_mod,
            no_body,
            help: (),
        });
    }

    /// Checks if `#[naked]` is applied to a function definition.
    fn check_naked(&self, hir_id: HirId, target: Target) {
        match target {
            Target::Fn
            | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => {
                let fn_sig = self.tcx.hir_node(hir_id).fn_sig().unwrap();
                let abi = fn_sig.header.abi;
                if abi.is_rustic_abi() && !self.tcx.features().naked_functions_rustic_abi() {
                    feature_err(
                        &self.tcx.sess,
                        sym::naked_functions_rustic_abi,
                        fn_sig.span,
                        format!(
                            "`#[naked]` is currently unstable on `extern \"{}\"` functions",
                            abi.as_str()
                        ),
                    )
                    .emit();
                }
            }
            _ => {}
        }
    }

    /// Debugging aid for `object_lifetime_default` query.
    fn check_object_lifetime_default(&self, hir_id: HirId) {
        let tcx = self.tcx;
        if let Some(owner_id) = hir_id.as_owner()
            && let Some(generics) = tcx.hir_get_generics(owner_id.def_id)
        {
            for p in generics.params {
                let hir::GenericParamKind::Type { .. } = p.kind else { continue };
                let default = tcx.object_lifetime_default(p.def_id);
                let repr = match default {
                    ObjectLifetimeDefault::Empty => "BaseDefault".to_owned(),
                    ObjectLifetimeDefault::Static => "'static".to_owned(),
                    ObjectLifetimeDefault::Param(def_id) => tcx.item_name(def_id).to_string(),
                    ObjectLifetimeDefault::Ambiguous => "Ambiguous".to_owned(),
                };
                tcx.dcx().emit_err(errors::ObjectLifetimeErr { span: p.span, repr });
            }
        }
    }
    /// Checks if `#[collapse_debuginfo]` is applied to a macro.
    fn check_collapse_debuginfo(&self, attr: &Attribute, span: Span, target: Target) {
        match target {
            Target::MacroDef => {}
            _ => {
                self.tcx.dcx().emit_err(errors::CollapseDebuginfo {
                    attr_span: attr.span(),
                    defn_span: span,
                });
            }
        }
    }

    /// Checks if a `#[track_caller]` is applied to a function.
    fn check_track_caller(
        &self,
        hir_id: HirId,
        attr_span: Span,
        attrs: &[Attribute],
        target: Target,
    ) {
        match target {
            Target::Fn => {
                // `#[track_caller]` is not valid on weak lang items because they are called via
                // `extern` declarations and `#[track_caller]` would alter their ABI.
                if let Some((lang_item, _)) = hir::lang_items::extract(attrs)
                    && let Some(item) = hir::LangItem::from_name(lang_item)
                    && item.is_weak()
                {
                    let sig = self.tcx.hir_node(hir_id).fn_sig().unwrap();

                    self.dcx().emit_err(errors::LangItemWithTrackCaller {
                        attr_span,
                        name: lang_item,
                        sig_span: sig.span,
                    });
                }

                if let Some(impls) = find_attr!(attrs, AttributeKind::EiiImpls(impls) => impls) {
                    let sig = self.tcx.hir_node(hir_id).fn_sig().unwrap();
                    for i in impls {
                        self.dcx().emit_err(errors::EiiWithTrackCaller {
                            attr_span,
                            name: self.tcx.item_name(i.eii_macro),
                            sig_span: sig.span,
                        });
                    }
                }
            }
            _ => {}
        }
    }

    /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid.
    fn check_non_exhaustive(
        &self,
        attr_span: Span,
        span: Span,
        target: Target,
        item: Option<ItemLike<'_>>,
    ) {
        match target {
            Target::Struct => {
                if let Some(ItemLike::Item(hir::Item {
                    kind: hir::ItemKind::Struct(_, _, hir::VariantData::Struct { fields, .. }),
                    ..
                })) = item
                    && !fields.is_empty()
                    && fields.iter().any(|f| f.default.is_some())
                {
                    self.dcx().emit_err(errors::NonExhaustiveWithDefaultFieldValues {
                        attr_span,
                        defn_span: span,
                    });
                }
            }
            _ => {}
        }
    }

    /// Checks if the `#[target_feature]` attribute on `item` is valid.
    fn check_target_feature(
        &self,
        hir_id: HirId,
        attr_span: Span,
        target: Target,
        attrs: &[Attribute],
    ) {
        match target {
            Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent)
            | Target::Fn => {
                // `#[target_feature]` is not allowed in lang items.
                if let Some((lang_item, _)) = hir::lang_items::extract(attrs)
                    // Calling functions with `#[target_feature]` is
                    // not unsafe on WASM, see #84988
                    && !self.tcx.sess.target.is_like_wasm
                    && !self.tcx.sess.opts.actually_rustdoc
                {
                    let sig = self.tcx.hir_node(hir_id).fn_sig().unwrap();

                    self.dcx().emit_err(errors::LangItemWithTargetFeature {
                        attr_span,
                        name: lang_item,
                        sig_span: sig.span,
                    });
                }
            }
            _ => {}
        }
    }

    /// Checks if the `#[thread_local]` attribute on `item` is valid.
    fn check_thread_local(&self, attr: &Attribute, span: Span, target: Target) {
        match target {
            Target::ForeignStatic | Target::Static => {}
            _ => {
                self.dcx().emit_err(errors::AttrShouldBeAppliedToStatic {
                    attr_span: attr.span(),
                    defn_span: span,
                });
            }
        }
    }

    fn check_doc_alias_value(&self, span: Span, hir_id: HirId, target: Target, alias: Symbol) {
        if let Some(location) = match target {
            Target::AssocTy => {
                if let DefKind::Impl { .. } =
                    self.tcx.def_kind(self.tcx.local_parent(hir_id.owner.def_id))
                {
                    Some("type alias in implementation block")
                } else {
                    None
                }
            }
            Target::AssocConst => {
                let parent_def_id = self.tcx.hir_get_parent_item(hir_id).def_id;
                let containing_item = self.tcx.hir_expect_item(parent_def_id);
                // We can't link to trait impl's consts.
                let err = "associated constant in trait implementation block";
                match containing_item.kind {
                    ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => Some(err),
                    _ => None,
                }
            }
            // we check the validity of params elsewhere
            Target::Param => return,
            Target::Expression
            | Target::Statement
            | Target::Arm
            | Target::ForeignMod
            | Target::Closure
            | Target::Impl { .. }
            | Target::WherePredicate => Some(target.name()),
            Target::ExternCrate
            | Target::Use
            | Target::Static
            | Target::Const
            | Target::Fn
            | Target::Mod
            | Target::GlobalAsm
            | Target::TyAlias
            | Target::Enum
            | Target::Variant
            | Target::Struct
            | Target::Field
            | Target::Union
            | Target::Trait
            | Target::TraitAlias
            | Target::Method(..)
            | Target::ForeignFn
            | Target::ForeignStatic
            | Target::ForeignTy
            | Target::GenericParam { .. }
            | Target::MacroDef
            | Target::PatField
            | Target::ExprField
            | Target::Crate
            | Target::MacroCall
            | Target::Delegation { .. } => None,
        } {
            self.tcx.dcx().emit_err(errors::DocAliasBadLocation { span, location });
            return;
        }
        if self.tcx.hir_opt_name(hir_id) == Some(alias) {
            self.tcx.dcx().emit_err(errors::DocAliasNotAnAlias { span, attr_str: alias });
            return;
        }
    }

    fn check_doc_fake_variadic(&self, span: Span, hir_id: HirId) {
        let item_kind = match self.tcx.hir_node(hir_id) {
            hir::Node::Item(item) => Some(&item.kind),
            _ => None,
        };
        match item_kind {
            Some(ItemKind::Impl(i)) => {
                let is_valid = doc_fake_variadic_is_allowed_self_ty(i.self_ty)
                    || if let Some(&[hir::GenericArg::Type(ty)]) = i
                        .of_trait
                        .and_then(|of_trait| of_trait.trait_ref.path.segments.last())
                        .map(|last_segment| last_segment.args().args)
                    {
                        matches!(&ty.kind, hir::TyKind::Tup([_]))
                    } else {
                        false
                    };
                if !is_valid {
                    self.dcx().emit_err(errors::DocFakeVariadicNotValid { span });
                }
            }
            _ => {
                self.dcx().emit_err(errors::DocKeywordOnlyImpl { span });
            }
        }
    }

    fn check_doc_search_unbox(&self, span: Span, hir_id: HirId) {
        let hir::Node::Item(item) = self.tcx.hir_node(hir_id) else {
            self.dcx().emit_err(errors::DocSearchUnboxInvalid { span });
            return;
        };
        match item.kind {
            ItemKind::Enum(_, generics, _) | ItemKind::Struct(_, generics, _)
                if generics.params.len() != 0 => {}
            ItemKind::Trait(_, _, _, _, generics, _, items)
                if generics.params.len() != 0
                    || items.iter().any(|item| {
                        matches!(self.tcx.def_kind(item.owner_id), DefKind::AssocTy)
                    }) => {}
            ItemKind::TyAlias(_, generics, _) if generics.params.len() != 0 => {}
            _ => {
                self.dcx().emit_err(errors::DocSearchUnboxInvalid { span });
            }
        }
    }

    /// Checks `#[doc(inline)]`/`#[doc(no_inline)]` attributes.
    ///
    /// A doc inlining attribute is invalid if it is applied to a non-`use` item, or
    /// if there are conflicting attributes for one item.
    ///
    /// `specified_inline` is used to keep track of whether we have
    /// already seen an inlining attribute for this item.
    /// If so, `specified_inline` holds the value and the span of
    /// the first `inline`/`no_inline` attribute.
    fn check_doc_inline(&self, hir_id: HirId, target: Target, inline: &[(DocInline, Span)]) {
        let span = match inline {
            [] => return,
            [(_, span)] => *span,
            [(inline, span), rest @ ..] => {
                for (inline2, span2) in rest {
                    if inline2 != inline {
                        let mut spans = MultiSpan::from_spans(vec![*span, *span2]);
                        spans.push_span_label(*span, fluent::passes_doc_inline_conflict_first);
                        spans.push_span_label(*span2, fluent::passes_doc_inline_conflict_second);
                        self.dcx().emit_err(errors::DocInlineConflict { spans });
                        return;
                    }
                }
                *span
            }
        };

        match target {
            Target::Use | Target::ExternCrate => {}
            _ => {
                self.tcx.emit_node_span_lint(
                    INVALID_DOC_ATTRIBUTES,
                    hir_id,
                    span,
                    errors::DocInlineOnlyUse {
                        attr_span: span,
                        item_span: self.tcx.hir_span(hir_id),
                    },
                );
            }
        }
    }

    fn check_doc_masked(&self, span: Span, hir_id: HirId, target: Target) {
        if target != Target::ExternCrate {
            self.tcx.emit_node_span_lint(
                INVALID_DOC_ATTRIBUTES,
                hir_id,
                span,
                errors::DocMaskedOnlyExternCrate {
                    attr_span: span,
                    item_span: self.tcx.hir_span(hir_id),
                },
            );
            return;
        }

        if self.tcx.extern_mod_stmt_cnum(hir_id.owner.def_id).is_none() {
            self.tcx.emit_node_span_lint(
                INVALID_DOC_ATTRIBUTES,
                hir_id,
                span,
                errors::DocMaskedNotExternCrateSelf {
                    attr_span: span,
                    item_span: self.tcx.hir_span(hir_id),
                },
            );
        }
    }

    fn check_doc_keyword_and_attribute(&self, span: Span, hir_id: HirId, attr_name: &'static str) {
        let item_kind = match self.tcx.hir_node(hir_id) {
            hir::Node::Item(item) => Some(&item.kind),
            _ => None,
        };
        match item_kind {
            Some(ItemKind::Mod(_, module)) => {
                if !module.item_ids.is_empty() {
                    self.dcx().emit_err(errors::DocKeywordAttributeEmptyMod { span, attr_name });
                    return;
                }
            }
            _ => {
                self.dcx().emit_err(errors::DocKeywordAttributeNotMod { span, attr_name });
                return;
            }
        }
    }

    /// Checks that an attribute is *not* used at the crate level. Returns `true` if valid.
    fn check_attr_not_crate_level(&self, span: Span, hir_id: HirId, attr_name: &str) -> bool {
        if CRATE_HIR_ID == hir_id {
            self.dcx().emit_err(errors::DocAttrNotCrateLevel { span, attr_name });
            return false;
        }
        true
    }

    /// Checks that an attribute is used at the crate level. Returns `true` if valid.
    fn check_attr_crate_level(&self, span: Span, hir_id: HirId) -> bool {
        if hir_id != CRATE_HIR_ID {
            self.tcx.emit_node_span_lint(
                INVALID_DOC_ATTRIBUTES,
                hir_id,
                span,
                errors::AttrCrateLevelOnly {},
            );
            return false;
        }
        true
    }

    /// Runs various checks on `#[doc]` attributes.
    ///
    /// `specified_inline` should be initialized to `None` and kept for the scope
    /// of one item. Read the documentation of [`check_doc_inline`] for more information.
    ///
    /// [`check_doc_inline`]: Self::check_doc_inline
    fn check_doc_attrs(&self, attr: &DocAttribute, hir_id: HirId, target: Target) {
        let DocAttribute {
            aliases,
            // valid pretty much anywhere, not checked here?
            // FIXME: should we?
            hidden: _,
            inline,
            // FIXME: currently unchecked
            cfg: _,
            // already check in attr_parsing
            auto_cfg: _,
            // already check in attr_parsing
            auto_cfg_change: _,
            fake_variadic,
            keyword,
            masked,
            // FIXME: currently unchecked
            notable_trait: _,
            search_unbox,
            html_favicon_url,
            html_logo_url,
            html_playground_url,
            html_root_url,
            html_no_source,
            issue_tracker_base_url,
            rust_logo,
            // allowed anywhere
            test_attrs: _,
            no_crate_inject,
            attribute,
        } = attr;

        for (alias, span) in aliases {
            if self.check_attr_not_crate_level(*span, hir_id, "alias") {
                self.check_doc_alias_value(*span, hir_id, target, *alias);
            }
        }

        if let Some((_, span)) = keyword
            && self.check_attr_not_crate_level(*span, hir_id, "keyword")
        {
            self.check_doc_keyword_and_attribute(*span, hir_id, "keyword");
        }
        if let Some((_, span)) = attribute
            && self.check_attr_not_crate_level(*span, hir_id, "attribute")
        {
            self.check_doc_keyword_and_attribute(*span, hir_id, "attribute");
        }

        if let Some(span) = fake_variadic
            && self.check_attr_not_crate_level(*span, hir_id, "fake_variadic")
        {
            self.check_doc_fake_variadic(*span, hir_id);
        }

        if let Some(span) = search_unbox
            && self.check_attr_not_crate_level(*span, hir_id, "search_unbox")
        {
            self.check_doc_search_unbox(*span, hir_id);
        }

        for i in [
            html_favicon_url,
            html_logo_url,
            html_playground_url,
            issue_tracker_base_url,
            html_root_url,
        ] {
            if let Some((_, span)) = i {
                self.check_attr_crate_level(*span, hir_id);
            }
        }

        for i in [html_no_source, no_crate_inject] {
            if let Some(span) = i {
                self.check_attr_crate_level(*span, hir_id);
            }
        }

        self.check_doc_inline(hir_id, target, inline);

        if let Some(span) = rust_logo
            && self.check_attr_crate_level(*span, hir_id)
            && !self.tcx.features().rustdoc_internals()
        {
            feature_err(
                &self.tcx.sess,
                sym::rustdoc_internals,
                *span,
                fluent::passes_doc_rust_logo,
            )
            .emit();
        }

        if let Some(span) = masked {
            self.check_doc_masked(*span, hir_id, target);
        }
    }

    fn check_has_incoherent_inherent_impls(&self, attr: &Attribute, span: Span, target: Target) {
        match target {
            Target::Trait | Target::Struct | Target::Enum | Target::Union | Target::ForeignTy => {}
            _ => {
                self.tcx
                    .dcx()
                    .emit_err(errors::HasIncoherentInherentImpl { attr_span: attr.span(), span });
            }
        }
    }

    fn check_ffi_pure(&self, attr_span: Span, attrs: &[Attribute]) {
        if find_attr!(attrs, AttributeKind::FfiConst(_)) {
            // `#[ffi_const]` functions cannot be `#[ffi_pure]`
            self.dcx().emit_err(errors::BothFfiConstAndPure { attr_span });
        }
    }

    /// Checks if `#[must_not_suspend]` is applied to a struct, enum, union, or trait.
    fn check_must_not_suspend(&self, attr: &Attribute, span: Span, target: Target) {
        match target {
            Target::Struct | Target::Enum | Target::Union | Target::Trait => {}
            _ => {
                self.dcx().emit_err(errors::MustNotSuspend { attr_span: attr.span(), span });
            }
        }
    }

    /// Checks if `#[may_dangle]` is applied to a lifetime or type generic parameter in `Drop` impl.
    fn check_may_dangle(&self, hir_id: HirId, attr_span: Span) {
        if let hir::Node::GenericParam(param) = self.tcx.hir_node(hir_id)
            && matches!(
                param.kind,
                hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. }
            )
            && matches!(param.source, hir::GenericParamSource::Generics)
            && let parent_hir_id = self.tcx.parent_hir_id(hir_id)
            && let hir::Node::Item(item) = self.tcx.hir_node(parent_hir_id)
            && let hir::ItemKind::Impl(impl_) = item.kind
            && let Some(of_trait) = impl_.of_trait
            && let Some(def_id) = of_trait.trait_ref.trait_def_id()
            && self.tcx.is_lang_item(def_id, hir::LangItem::Drop)
        {
            return;
        }

        self.dcx().emit_err(errors::InvalidMayDangle { attr_span });
    }

    /// Checks if `#[link]` is applied to an item other than a foreign module.
    fn check_link(&self, hir_id: HirId, attr_span: Span, span: Span, target: Target) {
        if target == Target::ForeignMod
            && let hir::Node::Item(item) = self.tcx.hir_node(hir_id)
            && let Item { kind: ItemKind::ForeignMod { abi, .. }, .. } = item
            && !matches!(abi, ExternAbi::Rust)
        {
            return;
        }

        self.tcx.emit_node_span_lint(
            UNUSED_ATTRIBUTES,
            hir_id,
            attr_span,
            errors::Link { span: (target != Target::ForeignMod).then_some(span) },
        );
    }

    /// Checks if `#[no_link]` is applied to an `extern crate`.
    fn check_no_link(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
        match target {
            Target::ExternCrate => {}
            // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
            // `#[no_link]` attribute with just a lint, because we previously
            // erroneously allowed it and some crates used it accidentally, to be compatible
            // with crates depending on them, we can't throw an error here.
            Target::Field | Target::Arm | Target::MacroDef => {
                self.inline_attr_str_error_with_macro_def(hir_id, attr.span(), "no_link");
            }
            _ => {
                self.dcx().emit_err(errors::NoLink { attr_span: attr.span(), span });
            }
        }
    }

    /// Checks if `#[rustc_legacy_const_generics]` is applied to a function and has a valid argument.
    fn check_rustc_legacy_const_generics(
        &self,
        hir_id: HirId,
        attr: &Attribute,
        span: Span,
        target: Target,
        item: Option<ItemLike<'_>>,
    ) {
        let is_function = matches!(target, Target::Fn);
        if !is_function {
            self.dcx().emit_err(errors::AttrShouldBeAppliedToFn {
                attr_span: attr.span(),
                defn_span: span,
                on_crate: hir_id == CRATE_HIR_ID,
            });
            return;
        }

        let Some(list) = attr.meta_item_list() else {
            // The attribute form is validated on AST.
            return;
        };

        let Some(ItemLike::Item(Item {
            kind: ItemKind::Fn { sig: FnSig { decl, .. }, generics, .. },
            ..
        })) = item
        else {
            bug!("should be a function item");
        };

        for param in generics.params {
            match param.kind {
                hir::GenericParamKind::Const { .. } => {}
                _ => {
                    self.dcx().emit_err(errors::RustcLegacyConstGenericsOnly {
                        attr_span: attr.span(),
                        param_span: param.span,
                    });
                    return;
                }
            }
        }

        if list.len() != generics.params.len() {
            self.dcx().emit_err(errors::RustcLegacyConstGenericsIndex {
                attr_span: attr.span(),
                generics_span: generics.span,
            });
            return;
        }

        let arg_count = decl.inputs.len() as u128 + generics.params.len() as u128;
        let mut invalid_args = vec![];
        for meta in list {
            if let Some(LitKind::Int(val, _)) = meta.lit().map(|lit| &lit.kind) {
                if *val >= arg_count {
                    let span = meta.span();
                    self.dcx().emit_err(errors::RustcLegacyConstGenericsIndexExceed {
                        span,
                        arg_count: arg_count as usize,
                    });
                    return;
                }
            } else {
                invalid_args.push(meta.span());
            }
        }

        if !invalid_args.is_empty() {
            self.dcx().emit_err(errors::RustcLegacyConstGenericsIndexNegative { invalid_args });
        }
    }

    /// Helper function for checking that the provided attribute is only applied to a function or
    /// method.
    fn check_applied_to_fn_or_method(
        &self,
        hir_id: HirId,
        attr_span: Span,
        defn_span: Span,
        target: Target,
    ) {
        let is_function = matches!(target, Target::Fn | Target::Method(..));
        if !is_function {
            self.dcx().emit_err(errors::AttrShouldBeAppliedToFn {
                attr_span,
                defn_span,
                on_crate: hir_id == CRATE_HIR_ID,
            });
        }
    }

    /// Checks that the `#[rustc_lint_opt_ty]` attribute is only applied to a struct.
    fn check_rustc_lint_opt_ty(&self, attr: &Attribute, span: Span, target: Target) {
        match target {
            Target::Struct => {}
            _ => {
                self.dcx().emit_err(errors::RustcLintOptTy { attr_span: attr.span(), span });
            }
        }
    }

    /// Checks that the `#[rustc_lint_opt_deny_field_access]` attribute is only applied to a field.
    fn check_rustc_lint_opt_deny_field_access(&self, attr: &Attribute, span: Span, target: Target) {
        match target {
            Target::Field => {}
            _ => {
                self.tcx
                    .dcx()
                    .emit_err(errors::RustcLintOptDenyFieldAccess { attr_span: attr.span(), span });
            }
        }
    }

    /// Checks that the dep-graph debugging attributes are only present when the query-dep-graph
    /// option is passed to the compiler.
    fn check_rustc_dirty_clean(&self, attr: &Attribute) {
        if !self.tcx.sess.opts.unstable_opts.query_dep_graph {
            self.dcx().emit_err(errors::RustcDirtyClean { span: attr.span() });
        }
    }

    /// Checks if the attribute is applied to a trait.
    fn check_must_be_applied_to_trait(&self, attr_span: Span, defn_span: Span, target: Target) {
        match target {
            Target::Trait => {}
            _ => {
                self.dcx().emit_err(errors::AttrShouldBeAppliedToTrait { attr_span, defn_span });
            }
        }
    }

    /// Checks if the `#[repr]` attributes on `item` are valid.
    fn check_repr(
        &self,
        attrs: &[Attribute],
        span: Span,
        target: Target,
        item: Option<ItemLike<'_>>,
        hir_id: HirId,
    ) {
        // Extract the names of all repr hints, e.g., [foo, bar, align] for:
        // ```
        // #[repr(foo)]
        // #[repr(bar, align(8))]
        // ```
        let (reprs, first_attr_span) = find_attr!(attrs, AttributeKind::Repr { reprs, first_span } => (reprs.as_slice(), Some(*first_span))).unwrap_or((&[], None));

        let mut int_reprs = 0;
        let mut is_explicit_rust = false;
        let mut is_c = false;
        let mut is_simd = false;
        let mut is_transparent = false;

        for (repr, repr_span) in reprs {
            match repr {
                ReprAttr::ReprRust => {
                    is_explicit_rust = true;
                    match target {
                        Target::Struct | Target::Union | Target::Enum => continue,
                        _ => {
                            self.dcx().emit_err(errors::AttrApplication::StructEnumUnion {
                                hint_span: *repr_span,
                                span,
                            });
                        }
                    }
                }
                ReprAttr::ReprC => {
                    is_c = true;
                    match target {
                        Target::Struct | Target::Union | Target::Enum => continue,
                        _ => {
                            self.dcx().emit_err(errors::AttrApplication::StructEnumUnion {
                                hint_span: *repr_span,
                                span,
                            });
                        }
                    }
                }
                ReprAttr::ReprAlign(align) => {
                    match target {
                        Target::Struct | Target::Union | Target::Enum => {}
                        Target::Fn | Target::Method(_) if self.tcx.features().fn_align() => {
                            self.dcx().emit_err(errors::ReprAlignShouldBeAlign {
                                span: *repr_span,
                                item: target.plural_name(),
                            });
                        }
                        Target::Static if self.tcx.features().static_align() => {
                            self.dcx().emit_err(errors::ReprAlignShouldBeAlignStatic {
                                span: *repr_span,
                                item: target.plural_name(),
                            });
                        }
                        _ => {
                            self.dcx().emit_err(errors::AttrApplication::StructEnumUnion {
                                hint_span: *repr_span,
                                span,
                            });
                        }
                    }

                    self.check_align(*align, *repr_span);
                }
                ReprAttr::ReprPacked(_) => {
                    if target != Target::Struct && target != Target::Union {
                        self.dcx().emit_err(errors::AttrApplication::StructUnion {
                            hint_span: *repr_span,
                            span,
                        });
                    } else {
                        continue;
                    }
                }
                ReprAttr::ReprSimd => {
                    is_simd = true;
                    if target != Target::Struct {
                        self.dcx().emit_err(errors::AttrApplication::Struct {
                            hint_span: *repr_span,
                            span,
                        });
                    } else {
                        continue;
                    }
                }
                ReprAttr::ReprTransparent => {
                    is_transparent = true;
                    match target {
                        Target::Struct | Target::Union | Target::Enum => continue,
                        _ => {
                            self.dcx().emit_err(errors::AttrApplication::StructEnumUnion {
                                hint_span: *repr_span,
                                span,
                            });
                        }
                    }
                }
                ReprAttr::ReprInt(_) => {
                    int_reprs += 1;
                    if target != Target::Enum {
                        self.dcx().emit_err(errors::AttrApplication::Enum {
                            hint_span: *repr_span,
                            span,
                        });
                    } else {
                        continue;
                    }
                }
            };
        }

        // catch `repr()` with no arguments, applied to an item (i.e. not `#![repr()]`)
        if let Some(first_attr_span) = first_attr_span
            && reprs.is_empty()
            && item.is_some()
        {
            match target {
                Target::Struct | Target::Union | Target::Enum => {}
                Target::Fn | Target::Method(_) => {
                    self.dcx().emit_err(errors::ReprAlignShouldBeAlign {
                        span: first_attr_span,
                        item: target.plural_name(),
                    });
                }
                _ => {
                    self.dcx().emit_err(errors::AttrApplication::StructEnumUnion {
                        hint_span: first_attr_span,
                        span,
                    });
                }
            }
            return;
        }

        // Just point at all repr hints if there are any incompatibilities.
        // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
        let hint_spans = reprs.iter().map(|(_, span)| *span);

        // Error on repr(transparent, <anything else>).
        if is_transparent && reprs.len() > 1 {
            let hint_spans = hint_spans.clone().collect();
            self.dcx().emit_err(errors::TransparentIncompatible {
                hint_spans,
                target: target.to_string(),
            });
        }
        // Error on `#[repr(transparent)]` in combination with
        // `#[rustc_pass_indirectly_in_non_rustic_abis]`
        if is_transparent
            && let Some(&pass_indirectly_span) =
                find_attr!(attrs, AttributeKind::RustcPassIndirectlyInNonRusticAbis(span) => span)
        {
            self.dcx().emit_err(errors::TransparentIncompatible {
                hint_spans: vec![span, pass_indirectly_span],
                target: target.to_string(),
            });
        }
        if is_explicit_rust && (int_reprs > 0 || is_c || is_simd) {
            let hint_spans = hint_spans.clone().collect();
            self.dcx().emit_err(errors::ReprConflicting { hint_spans });
        }
        // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
        if (int_reprs > 1)
            || (is_simd && is_c)
            || (int_reprs == 1
                && is_c
                && item.is_some_and(|item| {
                    if let ItemLike::Item(item) = item { is_c_like_enum(item) } else { false }
                }))
        {
            self.tcx.emit_node_span_lint(
                CONFLICTING_REPR_HINTS,
                hir_id,
                hint_spans.collect::<Vec<Span>>(),
                errors::ReprConflictingLint,
            );
        }
    }

    fn check_align(&self, align: Align, span: Span) {
        if align.bytes() > 2_u64.pow(29) {
            // for values greater than 2^29, a different error will be emitted, make sure that happens
            self.dcx().span_delayed_bug(
                span,
                "alignment greater than 2^29 should be errored on elsewhere",
            );
        } else {
            // only do this check when <= 2^29 to prevent duplicate errors:
            // alignment greater than 2^29 not supported
            // alignment is too large for the current target

            let max = Size::from_bits(self.tcx.sess.target.pointer_width).signed_int_max() as u64;
            if align.bytes() > max {
                self.dcx().emit_err(errors::InvalidReprAlignForTarget { span, size: max });
            }
        }
    }

    /// Outputs an error for attributes that can only be applied to macros, such as
    /// `#[allow_internal_unsafe]` and `#[allow_internal_unstable]`.
    /// (Allows proc_macro functions)
    // FIXME(jdonszelmann): if possible, move to attr parsing
    fn check_macro_only_attr(
        &self,
        attr_span: Span,
        span: Span,
        target: Target,
        attrs: &[Attribute],
    ) {
        match target {
            Target::Fn => {
                for attr in attrs {
                    if attr.is_proc_macro_attr() {
                        // return on proc macros
                        return;
                    }
                }
                self.tcx.dcx().emit_err(errors::MacroOnlyAttribute { attr_span, span });
            }
            _ => {}
        }
    }

    /// Outputs an error for `#[allow_internal_unstable]` which can only be applied to macros.
    /// (Allows proc_macro functions)
    fn check_rustc_allow_const_fn_unstable(
        &self,
        hir_id: HirId,
        attr_span: Span,
        span: Span,
        target: Target,
    ) {
        match target {
            Target::Fn | Target::Method(_) => {
                if !self.tcx.is_const_fn(hir_id.expect_owner().to_def_id()) {
                    self.tcx.dcx().emit_err(errors::RustcAllowConstFnUnstable { attr_span, span });
                }
            }
            _ => {}
        }
    }

    fn check_stability(
        &self,
        attr_span: Span,
        item_span: Span,
        level: &StabilityLevel,
        feature: Symbol,
    ) {
        // Stable *language* features shouldn't be used as unstable library features.
        // (Not doing this for stable library features is checked by tidy.)
        if level.is_unstable()
            && ACCEPTED_LANG_FEATURES.iter().find(|f| f.name == feature).is_some()
        {
            self.tcx
                .dcx()
                .emit_err(errors::UnstableAttrForAlreadyStableFeature { attr_span, item_span });
        }
    }

    fn check_deprecated(&self, hir_id: HirId, attr_span: Span, target: Target) {
        match target {
            Target::AssocConst | Target::Method(..) | Target::AssocTy
                if matches!(
                    self.tcx.def_kind(self.tcx.local_parent(hir_id.owner.def_id)),
                    DefKind::Impl { of_trait: true }
                ) =>
            {
                self.tcx.emit_node_span_lint(
                    UNUSED_ATTRIBUTES,
                    hir_id,
                    attr_span,
                    errors::DeprecatedAnnotationHasNoEffect { span: attr_span },
                );
            }
            _ => {}
        }
    }

    fn check_macro_export(&self, hir_id: HirId, attr_span: Span, target: Target) {
        if target != Target::MacroDef {
            return;
        }

        // special case when `#[macro_export]` is applied to a macro 2.0
        let (_, macro_definition, _) = self.tcx.hir_node(hir_id).expect_item().expect_macro();
        let is_decl_macro = !macro_definition.macro_rules;

        if is_decl_macro {
            self.tcx.emit_node_span_lint(
                UNUSED_ATTRIBUTES,
                hir_id,
                attr_span,
                errors::MacroExport::OnDeclMacro,
            );
        }
    }

    fn check_unused_attribute(&self, hir_id: HirId, attr: &Attribute, style: Option<AttrStyle>) {
        // Warn on useless empty attributes.
        // FIXME(jdonszelmann): this lint should be moved to attribute parsing, see `AcceptContext::warn_empty_attribute`
        let note = if attr.has_any_name(&[
            sym::allow,
            sym::expect,
            sym::warn,
            sym::deny,
            sym::forbid,
            sym::feature,
        ]) && attr.meta_item_list().is_some_and(|list| list.is_empty())
        {
            errors::UnusedNote::EmptyList { name: attr.name().unwrap() }
        } else if attr.has_any_name(&[sym::allow, sym::warn, sym::deny, sym::forbid, sym::expect])
            && let Some(meta) = attr.meta_item_list()
            && let [meta] = meta.as_slice()
            && let Some(item) = meta.meta_item()
            && let MetaItemKind::NameValue(_) = &item.kind
            && item.path == sym::reason
        {
            errors::UnusedNote::NoLints { name: attr.name().unwrap() }
        } else if attr.has_any_name(&[sym::allow, sym::warn, sym::deny, sym::forbid, sym::expect])
            && let Some(meta) = attr.meta_item_list()
            && meta.iter().any(|meta| {
                meta.meta_item().map_or(false, |item| item.path == sym::linker_messages)
            })
        {
            if hir_id != CRATE_HIR_ID {
                match style {
                    Some(ast::AttrStyle::Outer) => {
                        let attr_span = attr.span();
                        let bang_position = self
                            .tcx
                            .sess
                            .source_map()
                            .span_until_char(attr_span, '[')
                            .shrink_to_hi();

                        self.tcx.emit_node_span_lint(
                            UNUSED_ATTRIBUTES,
                            hir_id,
                            attr_span,
                            errors::OuterCrateLevelAttr {
                                suggestion: errors::OuterCrateLevelAttrSuggestion { bang_position },
                            },
                        )
                    }
                    Some(ast::AttrStyle::Inner) | None => self.tcx.emit_node_span_lint(
                        UNUSED_ATTRIBUTES,
                        hir_id,
                        attr.span(),
                        errors::InnerCrateLevelAttr,
                    ),
                };
                return;
            } else {
                let never_needs_link = self
                    .tcx
                    .crate_types()
                    .iter()
                    .all(|kind| matches!(kind, CrateType::Rlib | CrateType::Staticlib));
                if never_needs_link {
                    errors::UnusedNote::LinkerMessagesBinaryCrateOnly
                } else {
                    return;
                }
            }
        } else if attr.has_name(sym::default_method_body_is_const) {
            errors::UnusedNote::DefaultMethodBodyConst
        } else {
            return;
        };

        self.tcx.emit_node_span_lint(
            UNUSED_ATTRIBUTES,
            hir_id,
            attr.span(),
            errors::Unused { attr_span: attr.span(), note },
        );
    }

    /// A best effort attempt to create an error for a mismatching proc macro signature.
    ///
    /// If this best effort goes wrong, it will just emit a worse error later (see #102923)
    fn check_proc_macro(&self, hir_id: HirId, target: Target, kind: ProcMacroKind) {
        if target != Target::Fn {
            return;
        }

        let tcx = self.tcx;
        let Some(token_stream_def_id) = tcx.get_diagnostic_item(sym::TokenStream) else {
            return;
        };
        let Some(token_stream) = tcx.type_of(token_stream_def_id).no_bound_vars() else {
            return;
        };

        let def_id = hir_id.expect_owner().def_id;
        let param_env = ty::ParamEnv::empty();

        let infcx = tcx.infer_ctxt().build(TypingMode::non_body_analysis());
        let ocx = ObligationCtxt::new_with_diagnostics(&infcx);

        let span = tcx.def_span(def_id);
        let fresh_args = infcx.fresh_args_for_item(span, def_id.to_def_id());
        let sig = tcx.liberate_late_bound_regions(
            def_id.to_def_id(),
            tcx.fn_sig(def_id).instantiate(tcx, fresh_args),
        );

        let mut cause = ObligationCause::misc(span, def_id);
        let sig = ocx.normalize(&cause, param_env, sig);

        // proc macro is not WF.
        let errors = ocx.try_evaluate_obligations();
        if !errors.is_empty() {
            return;
        }

        let expected_sig = tcx.mk_fn_sig(
            std::iter::repeat_n(
                token_stream,
                match kind {
                    ProcMacroKind::Attribute => 2,
                    ProcMacroKind::Derive | ProcMacroKind::FunctionLike => 1,
                },
            ),
            token_stream,
            false,
            Safety::Safe,
            ExternAbi::Rust,
        );

        if let Err(terr) = ocx.eq(&cause, param_env, expected_sig, sig) {
            let mut diag = tcx.dcx().create_err(errors::ProcMacroBadSig { span, kind });

            let hir_sig = tcx.hir_fn_sig_by_hir_id(hir_id);
            if let Some(hir_sig) = hir_sig {
                #[allow(rustc::diagnostic_outside_of_impl)] // FIXME
                match terr {
                    TypeError::ArgumentMutability(idx) | TypeError::ArgumentSorts(_, idx) => {
                        if let Some(ty) = hir_sig.decl.inputs.get(idx) {
                            diag.span(ty.span);
                            cause.span = ty.span;
                        } else if idx == hir_sig.decl.inputs.len() {
                            let span = hir_sig.decl.output.span();
                            diag.span(span);
                            cause.span = span;
                        }
                    }
                    TypeError::ArgCount => {
                        if let Some(ty) = hir_sig.decl.inputs.get(expected_sig.inputs().len()) {
                            diag.span(ty.span);
                            cause.span = ty.span;
                        }
                    }
                    TypeError::SafetyMismatch(_) => {
                        // FIXME: Would be nice if we had a span here..
                    }
                    TypeError::AbiMismatch(_) => {
                        // FIXME: Would be nice if we had a span here..
                    }
                    TypeError::VariadicMismatch(_) => {
                        // FIXME: Would be nice if we had a span here..
                    }
                    _ => {}
                }
            }

            infcx.err_ctxt().note_type_err(
                &mut diag,
                &cause,
                None,
                Some(param_env.and(ValuePairs::PolySigs(ExpectedFound {
                    expected: ty::Binder::dummy(expected_sig),
                    found: ty::Binder::dummy(sig),
                }))),
                terr,
                false,
                None,
            );
            diag.emit();
            self.abort.set(true);
        }

        let errors = ocx.evaluate_obligations_error_on_ambiguity();
        if !errors.is_empty() {
            infcx.err_ctxt().report_fulfillment_errors(errors);
            self.abort.set(true);
        }
    }

    fn check_rustc_pub_transparent(&self, attr_span: Span, span: Span, attrs: &[Attribute]) {
        if !find_attr!(attrs, AttributeKind::Repr { reprs, .. } => reprs.iter().any(|(r, _)| r == &ReprAttr::ReprTransparent))
            .unwrap_or(false)
        {
            self.dcx().emit_err(errors::RustcPubTransparent { span, attr_span });
        }
    }

    fn check_rustc_force_inline(&self, hir_id: HirId, attrs: &[Attribute], target: Target) {
        if let (Target::Closure, None) = (
            target,
            find_attr!(attrs, AttributeKind::Inline(InlineAttr::Force { attr_span, .. }, _) => *attr_span),
        ) {
            let is_coro = matches!(
                self.tcx.hir_expect_expr(hir_id).kind,
                hir::ExprKind::Closure(hir::Closure {
                    kind: hir::ClosureKind::Coroutine(..) | hir::ClosureKind::CoroutineClosure(..),
                    ..
                })
            );
            let parent_did = self.tcx.hir_get_parent_item(hir_id).to_def_id();
            let parent_span = self.tcx.def_span(parent_did);

            if let Some(attr_span) = find_attr!(
                self.tcx.get_all_attrs(parent_did),
                AttributeKind::Inline(InlineAttr::Force { attr_span, .. }, _) => *attr_span
            ) && is_coro
            {
                self.dcx().emit_err(errors::RustcForceInlineCoro { attr_span, span: parent_span });
            }
        }
    }

    fn check_mix_no_mangle_export(&self, hir_id: HirId, attrs: &[Attribute]) {
        if let Some(export_name_span) = find_attr!(attrs, AttributeKind::ExportName { span: export_name_span, .. } => *export_name_span)
            && let Some(no_mangle_span) =
                find_attr!(attrs, AttributeKind::NoMangle(no_mangle_span) => *no_mangle_span)
        {
            let no_mangle_attr = if no_mangle_span.edition() >= Edition::Edition2024 {
                "#[unsafe(no_mangle)]"
            } else {
                "#[no_mangle]"
            };
            let export_name_attr = if export_name_span.edition() >= Edition::Edition2024 {
                "#[unsafe(export_name)]"
            } else {
                "#[export_name]"
            };

            self.tcx.emit_node_span_lint(
                lint::builtin::UNUSED_ATTRIBUTES,
                hir_id,
                no_mangle_span,
                errors::MixedExportNameAndNoMangle {
                    no_mangle_span,
                    export_name_span,
                    no_mangle_attr,
                    export_name_attr,
                },
            );
        }
    }

    /// Checks if `#[autodiff]` is applied to an item other than a function item.
    fn check_autodiff(&self, _hir_id: HirId, _attr: &Attribute, span: Span, target: Target) {
        debug!("check_autodiff");
        match target {
            Target::Fn => {}
            _ => {
                self.dcx().emit_err(errors::AutoDiffAttr { attr_span: span });
                self.abort.set(true);
            }
        }
    }

    fn check_loop_match(&self, hir_id: HirId, attr_span: Span, target: Target) {
        let node_span = self.tcx.hir_span(hir_id);

        if !matches!(target, Target::Expression) {
            return; // Handled in target checking during attr parse
        }

        if !matches!(self.tcx.hir_expect_expr(hir_id).kind, hir::ExprKind::Loop(..)) {
            self.dcx().emit_err(errors::LoopMatchAttr { attr_span, node_span });
        };
    }

    fn check_const_continue(&self, hir_id: HirId, attr_span: Span, target: Target) {
        let node_span = self.tcx.hir_span(hir_id);

        if !matches!(target, Target::Expression) {
            return; // Handled in target checking during attr parse
        }

        if !matches!(self.tcx.hir_expect_expr(hir_id).kind, hir::ExprKind::Break(..)) {
            self.dcx().emit_err(errors::ConstContinueAttr { attr_span, node_span });
        };
    }

    fn check_custom_mir(
        &self,
        dialect: Option<(MirDialect, Span)>,
        phase: Option<(MirPhase, Span)>,
        attr_span: Span,
    ) {
        let Some((dialect, dialect_span)) = dialect else {
            if let Some((_, phase_span)) = phase {
                self.dcx()
                    .emit_err(errors::CustomMirPhaseRequiresDialect { attr_span, phase_span });
            }
            return;
        };

        match dialect {
            MirDialect::Analysis => {
                if let Some((MirPhase::Optimized, phase_span)) = phase {
                    self.dcx().emit_err(errors::CustomMirIncompatibleDialectAndPhase {
                        dialect,
                        phase: MirPhase::Optimized,
                        attr_span,
                        dialect_span,
                        phase_span,
                    });
                }
            }

            MirDialect::Built => {
                if let Some((phase, phase_span)) = phase {
                    self.dcx().emit_err(errors::CustomMirIncompatibleDialectAndPhase {
                        dialect,
                        phase,
                        attr_span,
                        dialect_span,
                        phase_span,
                    });
                }
            }
            MirDialect::Runtime => {}
        }
    }
}

impl<'tcx> Visitor<'tcx> for CheckAttrVisitor<'tcx> {
    type NestedFilter = nested_filter::OnlyBodies;

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

    fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
        // Historically we've run more checks on non-exported than exported macros,
        // so this lets us continue to run them while maintaining backwards compatibility.
        // In the long run, the checks should be harmonized.
        if let ItemKind::Macro(_, macro_def, _) = item.kind {
            let def_id = item.owner_id.to_def_id();
            if macro_def.macro_rules
                && !find_attr!(self.tcx.get_all_attrs(def_id), AttributeKind::MacroExport { .. })
            {
                check_non_exported_macro_for_invalid_attrs(self.tcx, item);
            }
        }

        let target = Target::from_item(item);
        self.check_attributes(item.hir_id(), item.span, target, Some(ItemLike::Item(item)));
        intravisit::walk_item(self, item)
    }

    fn visit_where_predicate(&mut self, where_predicate: &'tcx hir::WherePredicate<'tcx>) {
        // FIXME(where_clause_attrs): Currently, as the following check shows,
        // only `#[cfg]` and `#[cfg_attr]` are allowed, but it should be removed
        // if we allow more attributes (e.g., tool attributes and `allow/deny/warn`)
        // in where clauses. After that, only `self.check_attributes` should be enough.
        const ATTRS_ALLOWED: &[Symbol] = &[sym::cfg_trace, sym::cfg_attr_trace];
        let spans = self
            .tcx
            .hir_attrs(where_predicate.hir_id)
            .iter()
            .filter(|attr| !ATTRS_ALLOWED.iter().any(|&sym| attr.has_name(sym)))
            // FIXME: We shouldn't need to special-case `doc`!
            .filter(|attr| {
                matches!(
                    attr,
                    Attribute::Parsed(AttributeKind::DocComment { .. } | AttributeKind::Doc(_))
                        | Attribute::Unparsed(_)
                )
            })
            .map(|attr| attr.span())
            .collect::<Vec<_>>();
        if !spans.is_empty() {
            self.tcx.dcx().emit_err(errors::UnsupportedAttributesInWhere { span: spans.into() });
        }
        self.check_attributes(
            where_predicate.hir_id,
            where_predicate.span,
            Target::WherePredicate,
            None,
        );
        intravisit::walk_where_predicate(self, where_predicate)
    }

    fn visit_generic_param(&mut self, generic_param: &'tcx hir::GenericParam<'tcx>) {
        let target = Target::from_generic_param(generic_param);
        self.check_attributes(generic_param.hir_id, generic_param.span, target, None);
        intravisit::walk_generic_param(self, generic_param)
    }

    fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
        let target = Target::from_trait_item(trait_item);
        self.check_attributes(trait_item.hir_id(), trait_item.span, target, None);
        intravisit::walk_trait_item(self, trait_item)
    }

    fn visit_field_def(&mut self, struct_field: &'tcx hir::FieldDef<'tcx>) {
        self.check_attributes(struct_field.hir_id, struct_field.span, Target::Field, None);
        intravisit::walk_field_def(self, struct_field);
    }

    fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
        self.check_attributes(arm.hir_id, arm.span, Target::Arm, None);
        intravisit::walk_arm(self, arm);
    }

    fn visit_foreign_item(&mut self, f_item: &'tcx ForeignItem<'tcx>) {
        let target = Target::from_foreign_item(f_item);
        self.check_attributes(f_item.hir_id(), f_item.span, target, Some(ItemLike::ForeignItem));
        intravisit::walk_foreign_item(self, f_item)
    }

    fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
        let target = target_from_impl_item(self.tcx, impl_item);
        self.check_attributes(impl_item.hir_id(), impl_item.span, target, None);
        intravisit::walk_impl_item(self, impl_item)
    }

    fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
        // When checking statements ignore expressions, they will be checked later.
        if let hir::StmtKind::Let(l) = stmt.kind {
            self.check_attributes(l.hir_id, stmt.span, Target::Statement, None);
        }
        intravisit::walk_stmt(self, stmt)
    }

    fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
        let target = match expr.kind {
            hir::ExprKind::Closure { .. } => Target::Closure,
            _ => Target::Expression,
        };

        self.check_attributes(expr.hir_id, expr.span, target, None);
        intravisit::walk_expr(self, expr)
    }

    fn visit_expr_field(&mut self, field: &'tcx hir::ExprField<'tcx>) {
        self.check_attributes(field.hir_id, field.span, Target::ExprField, None);
        intravisit::walk_expr_field(self, field)
    }

    fn visit_variant(&mut self, variant: &'tcx hir::Variant<'tcx>) {
        self.check_attributes(variant.hir_id, variant.span, Target::Variant, None);
        intravisit::walk_variant(self, variant)
    }

    fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
        self.check_attributes(param.hir_id, param.span, Target::Param, None);

        intravisit::walk_param(self, param);
    }

    fn visit_pat_field(&mut self, field: &'tcx hir::PatField<'tcx>) {
        self.check_attributes(field.hir_id, field.span, Target::PatField, None);
        intravisit::walk_pat_field(self, field);
    }
}

fn is_c_like_enum(item: &Item<'_>) -> bool {
    if let ItemKind::Enum(_, _, ref def) = item.kind {
        for variant in def.variants {
            match variant.data {
                hir::VariantData::Unit(..) => { /* continue */ }
                _ => return false,
            }
        }
        true
    } else {
        false
    }
}

// FIXME: Fix "Cannot determine resolution" error and remove built-in macros
// from this check.
fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
    // Check for builtin attributes at the crate level
    // which were unsuccessfully resolved due to cannot determine
    // resolution for the attribute macro error.
    const ATTRS_TO_CHECK: &[Symbol] =
        &[sym::derive, sym::test, sym::test_case, sym::global_allocator, sym::bench];

    for attr in attrs {
        // FIXME(jdonszelmann): all attrs should be combined here cleaning this up some day.
        let (span, name) = if let Some(a) =
            ATTRS_TO_CHECK.iter().find(|attr_to_check| attr.has_name(**attr_to_check))
        {
            (attr.span(), *a)
        } else if let Attribute::Parsed(AttributeKind::Repr {
            reprs: _,
            first_span: first_attr_span,
        }) = attr
        {
            (*first_attr_span, sym::repr)
        } else {
            continue;
        };

        let item = tcx
            .hir_free_items()
            .map(|id| tcx.hir_item(id))
            .find(|item| !item.span.is_dummy()) // Skip prelude `use`s
            .map(|item| errors::ItemFollowingInnerAttr {
                span: if let Some(ident) = item.kind.ident() { ident.span } else { item.span },
                kind: tcx.def_descr(item.owner_id.to_def_id()),
            });
        let err = tcx.dcx().create_err(errors::InvalidAttrAtCrateLevel {
            span,
            sugg_span: tcx
                .sess
                .source_map()
                .span_to_snippet(span)
                .ok()
                .filter(|src| src.starts_with("#!["))
                .map(|_| span.with_lo(span.lo() + BytePos(1)).with_hi(span.lo() + BytePos(2))),
            name,
            item,
        });

        if let Attribute::Unparsed(p) = attr {
            tcx.dcx().try_steal_replace_and_emit_err(
                p.path.span,
                StashKey::UndeterminedMacroResolution,
                err,
            );
        } else {
            err.emit();
        }
    }
}

fn check_non_exported_macro_for_invalid_attrs(tcx: TyCtxt<'_>, item: &Item<'_>) {
    let attrs = tcx.hir_attrs(item.hir_id());

    if let Some(attr_span) = find_attr!(attrs, AttributeKind::Inline(i, span) if !matches!(i, InlineAttr::Force{..}) => *span)
    {
        tcx.dcx().emit_err(errors::NonExportedMacroInvalidAttrs { attr_span });
    }
}

fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: LocalModDefId) {
    let check_attr_visitor = &mut CheckAttrVisitor { tcx, abort: Cell::new(false) };
    tcx.hir_visit_item_likes_in_module(module_def_id, check_attr_visitor);
    if module_def_id.to_local_def_id().is_top_level_module() {
        check_attr_visitor.check_attributes(CRATE_HIR_ID, DUMMY_SP, Target::Mod, None);
        check_invalid_crate_level_attr(tcx, tcx.hir_krate_attrs());
    }
    if check_attr_visitor.abort.get() {
        tcx.dcx().abort_if_errors()
    }
}

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

// FIXME(jdonszelmann): remove, check during parsing
fn check_duplicates(
    tcx: TyCtxt<'_>,
    attr_span: Span,
    attr: &Attribute,
    hir_id: HirId,
    duplicates: AttributeDuplicates,
    seen: &mut FxHashMap<Symbol, Span>,
) {
    use AttributeDuplicates::*;
    if matches!(duplicates, WarnFollowingWordOnly) && !attr.is_word() {
        return;
    }
    let attr_name = attr.name().unwrap();
    match duplicates {
        DuplicatesOk => {}
        WarnFollowing | FutureWarnFollowing | WarnFollowingWordOnly | FutureWarnPreceding => {
            match seen.entry(attr_name) {
                Entry::Occupied(mut entry) => {
                    let (this, other) = if matches!(duplicates, FutureWarnPreceding) {
                        let to_remove = entry.insert(attr_span);
                        (to_remove, attr_span)
                    } else {
                        (attr_span, *entry.get())
                    };
                    tcx.emit_node_span_lint(
                        UNUSED_ATTRIBUTES,
                        hir_id,
                        this,
                        errors::UnusedDuplicate {
                            this,
                            other,
                            warning: matches!(
                                duplicates,
                                FutureWarnFollowing | FutureWarnPreceding
                            ),
                        },
                    );
                }
                Entry::Vacant(entry) => {
                    entry.insert(attr_span);
                }
            }
        }
        ErrorFollowing | ErrorPreceding => match seen.entry(attr_name) {
            Entry::Occupied(mut entry) => {
                let (this, other) = if matches!(duplicates, ErrorPreceding) {
                    let to_remove = entry.insert(attr_span);
                    (to_remove, attr_span)
                } else {
                    (attr_span, *entry.get())
                };
                tcx.dcx().emit_err(errors::UnusedMultiple { this, other, name: attr_name });
            }
            Entry::Vacant(entry) => {
                entry.insert(attr_span);
            }
        },
    }
}

fn doc_fake_variadic_is_allowed_self_ty(self_ty: &hir::Ty<'_>) -> bool {
    matches!(&self_ty.kind, hir::TyKind::Tup([_]))
        || if let hir::TyKind::FnPtr(fn_ptr_ty) = &self_ty.kind {
            fn_ptr_ty.decl.inputs.len() == 1
        } else {
            false
        }
        || (if let hir::TyKind::Path(hir::QPath::Resolved(_, path)) = &self_ty.kind
            && let Some(&[hir::GenericArg::Type(ty)]) =
                path.segments.last().map(|last| last.args().args)
        {
            doc_fake_variadic_is_allowed_self_ty(ty.as_unambig_ty())
        } else {
            false
        })
}