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, MetaItemInner, MetaItemKind, ast};
use rustc_attr_parsing::{AttributeParser, Late};
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{Applicability, DiagCtxtHandle, IntoDiagArg, MultiSpan, StashKey};
use rustc_feature::{
    ACCEPTED_LANG_FEATURES, AttributeDuplicates, AttributeType, BUILTIN_ATTRIBUTE_MAP,
    BuiltinAttribute,
};
use rustc_hir::attrs::{AttributeKind, InlineAttr, ReprAttr};
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, CRATE_OWNER_ID, 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, INVALID_MACRO_EXPORT_ARGUMENTS,
    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, edition, 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;

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 doc_aliases = FxHashMap::default();
        let mut specified_inline = None;
        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::TypeConst(attr_span)) => {
                    self.check_type_const(hir_id, attr_span, target)
                }
                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 { .. }) => {
                    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::MustUse { span, .. }) => {
                    self.check_must_use(hir_id, *span, target)
                }
                Attribute::Parsed(
                    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::ConstTrait(..)
                    | AttributeKind::DenyExplicitImpl(..)
                    | AttributeKind::DoNotImplementViaObject(..)
                    | AttributeKind::SpecializationTrait(..)
                    | AttributeKind::UnsafeSpecializationMarker(..)
                    | AttributeKind::ParenSugar(..)
                    | AttributeKind::AllowIncoherentImpl(..)
                    | AttributeKind::Confusables { .. }
                    // `#[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::CoherenceIsCore
                    | AttributeKind::Fundamental
                    | AttributeKind::Optimize(..)
                    | AttributeKind::LinkSection { .. }
                    | AttributeKind::MacroUse { .. }
                    | AttributeKind::MacroEscape( .. )
                    | AttributeKind::RustcLayoutScalarValidRangeStart(..)
                    | AttributeKind::RustcLayoutScalarValidRangeEnd(..)
                    | 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(..),
                ) => { /* 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::no_sanitize, ..] => {
                            self.check_no_sanitize(attr, span, target)
                        }
                        [sym::thread_local, ..] => self.check_thread_local(attr, span, target),
                        [sym::doc, ..] => self.check_doc_attrs(
                            attr,
                            attr_item.style,
                            hir_id,
                            target,
                            &mut specified_inline,
                            &mut doc_aliases,
                        ),
                        [sym::no_link, ..] => self.check_no_link(hir_id, attr, span, target),
                        [sym::debugger_visualizer, ..] => self.check_debugger_visualizer(attr, 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::link, ..] => self.check_link(hir_id, attr, span, target),
                        [sym::macro_export, ..] => self.check_macro_export(hir_id, attr, 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::windows_subsystem // 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
                            | sym::custom_mir,
                            ..
                        ] => {}
                        [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!(),
                    }
                }
            }

            let builtin = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));

            if hir_id != CRATE_HIR_ID {
                if let Some(BuiltinAttribute { type_: AttributeType::CrateLevel, .. }) =
                    attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name))
                {
                    match style {
                        Some(ast::AttrStyle::Outer) => self.tcx.emit_node_span_lint(
                            UNUSED_ATTRIBUTES,
                            hir_id,
                            attr.span(),
                            errors::OuterCrateLevelAttr,
                        ),
                        Some(ast::AttrStyle::Inner) | None => self.tcx.emit_node_span_lint(
                            UNUSED_ATTRIBUTES,
                            hir_id,
                            attr.span(),
                            errors::InnerCrateLevelAttr,
                        ),
                    }
                }
            }

            if let Some(BuiltinAttribute { duplicates, .. }) = builtin {
                check_duplicates(self.tcx, 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 },
        );
    }

    /// 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 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, did.into()) {
                        self.tcx.emit_node_span_lint(
                            UNUSED_ATTRIBUTES,
                            hir_id,
                            attr_span,
                            errors::InlineIgnoredForExported {},
                        );
                    }
                }
            }
            _ => {}
        }
    }

    fn check_no_sanitize(&self, attr: &Attribute, span: Span, target: Target) {
        if let Some(list) = attr.meta_item_list() {
            for item in list.iter() {
                let sym = item.name();
                match sym {
                    Some(s @ sym::address | s @ sym::hwaddress) => {
                        let is_valid =
                            matches!(target, Target::Fn | Target::Method(..) | Target::Static);
                        if !is_valid {
                            self.dcx().emit_err(errors::NoSanitize {
                                attr_span: item.span(),
                                defn_span: span,
                                accepted_kind: "a function or static",
                                attr_str: s.as_str(),
                            });
                        }
                    }
                    _ => {
                        let is_valid = matches!(target, Target::Fn | Target::Method(..));
                        if !is_valid {
                            self.dcx().emit_err(errors::NoSanitize {
                                attr_span: item.span(),
                                defn_span: span,
                                accepted_kind: "a function",
                                attr_str: &match sym {
                                    Some(name) => name.to_string(),
                                    None => "...".to_string(),
                                },
                            });
                        }
                    }
                }
            }
        }
    }

    /// 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,
                    });
                }
            }
            _ => {}
        }
    }

    /// 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 doc_attr_str_error(&self, meta: &MetaItemInner, attr_name: &str) {
        self.dcx().emit_err(errors::DocExpectStr { attr_span: meta.span(), attr_name });
    }

    fn check_doc_alias_value(
        &self,
        meta: &MetaItemInner,
        doc_alias: Symbol,
        hir_id: HirId,
        target: Target,
        is_list: bool,
        aliases: &mut FxHashMap<String, Span>,
    ) {
        let tcx = self.tcx;
        let span = meta.name_value_literal_span().unwrap_or_else(|| meta.span());
        let attr_str =
            &format!("`#[doc(alias{})]`", if is_list { "(\"...\")" } else { " = \"...\"" });
        if doc_alias == sym::empty {
            tcx.dcx().emit_err(errors::DocAliasEmpty { span, attr_str });
            return;
        }

        let doc_alias_str = doc_alias.as_str();
        if let Some(c) = doc_alias_str
            .chars()
            .find(|&c| c == '"' || c == '\'' || (c.is_whitespace() && c != ' '))
        {
            tcx.dcx().emit_err(errors::DocAliasBadChar { span, attr_str, char_: c });
            return;
        }
        if doc_alias_str.starts_with(' ') || doc_alias_str.ends_with(' ') {
            tcx.dcx().emit_err(errors::DocAliasStartEnd { span, attr_str });
            return;
        }

        let span = meta.span();
        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,
        } {
            tcx.dcx().emit_err(errors::DocAliasBadLocation { span, attr_str, location });
            return;
        }
        if self.tcx.hir_opt_name(hir_id) == Some(doc_alias) {
            tcx.dcx().emit_err(errors::DocAliasNotAnAlias { span, attr_str });
            return;
        }
        if let Err(entry) = aliases.try_insert(doc_alias_str.to_owned(), span) {
            self.tcx.emit_node_span_lint(
                UNUSED_ATTRIBUTES,
                hir_id,
                span,
                errors::DocAliasDuplicated { first_defn: *entry.entry.get() },
            );
        }
    }

    fn check_doc_alias(
        &self,
        meta: &MetaItemInner,
        hir_id: HirId,
        target: Target,
        aliases: &mut FxHashMap<String, Span>,
    ) {
        if let Some(values) = meta.meta_item_list() {
            for v in values {
                match v.lit() {
                    Some(l) => match l.kind {
                        LitKind::Str(s, _) => {
                            self.check_doc_alias_value(v, s, hir_id, target, true, aliases);
                        }
                        _ => {
                            self.tcx
                                .dcx()
                                .emit_err(errors::DocAliasNotStringLiteral { span: v.span() });
                        }
                    },
                    None => {
                        self.tcx
                            .dcx()
                            .emit_err(errors::DocAliasNotStringLiteral { span: v.span() });
                    }
                }
            }
        } else if let Some(doc_alias) = meta.value_str() {
            self.check_doc_alias_value(meta, doc_alias, hir_id, target, false, aliases)
        } else {
            self.dcx().emit_err(errors::DocAliasMalformed { span: meta.span() });
        }
    }

    fn check_doc_keyword(&self, meta: &MetaItemInner, hir_id: HirId) {
        fn is_doc_keyword(s: Symbol) -> bool {
            // FIXME: Once rustdoc can handle URL conflicts on case insensitive file systems, we
            // can remove the `SelfTy` case here, remove `sym::SelfTy`, and update the
            // `#[doc(keyword = "SelfTy")` attribute in `library/std/src/keyword_docs.rs`.
            s.is_reserved(|| edition::LATEST_STABLE_EDITION) || s.is_weak() || s == sym::SelfTy
        }

        let doc_keyword = match meta.value_str() {
            Some(value) if value != sym::empty => value,
            _ => return self.doc_attr_str_error(meta, "keyword"),
        };

        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::DocKeywordEmptyMod { span: meta.span() });
                    return;
                }
            }
            _ => {
                self.dcx().emit_err(errors::DocKeywordNotMod { span: meta.span() });
                return;
            }
        }
        if !is_doc_keyword(doc_keyword) {
            self.dcx().emit_err(errors::DocKeywordNotKeyword {
                span: meta.name_value_literal_span().unwrap_or_else(|| meta.span()),
                keyword: doc_keyword,
            });
        }
    }

    fn check_doc_fake_variadic(&self, meta: &MetaItemInner, 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: meta.span() });
                }
            }
            _ => {
                self.dcx().emit_err(errors::DocKeywordOnlyImpl { span: meta.span() });
            }
        }
    }

    fn check_doc_search_unbox(&self, meta: &MetaItemInner, hir_id: HirId) {
        let hir::Node::Item(item) = self.tcx.hir_node(hir_id) else {
            self.dcx().emit_err(errors::DocSearchUnboxInvalid { span: meta.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: meta.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,
        style: AttrStyle,
        meta: &MetaItemInner,
        hir_id: HirId,
        target: Target,
        specified_inline: &mut Option<(bool, Span)>,
    ) {
        match target {
            Target::Use | Target::ExternCrate => {
                let do_inline = meta.has_name(sym::inline);
                if let Some((prev_inline, prev_span)) = *specified_inline {
                    if do_inline != prev_inline {
                        let mut spans = MultiSpan::from_spans(vec![prev_span, meta.span()]);
                        spans.push_span_label(prev_span, fluent::passes_doc_inline_conflict_first);
                        spans.push_span_label(
                            meta.span(),
                            fluent::passes_doc_inline_conflict_second,
                        );
                        self.dcx().emit_err(errors::DocKeywordConflict { spans });
                    }
                } else {
                    *specified_inline = Some((do_inline, meta.span()));
                }
            }
            _ => {
                self.tcx.emit_node_span_lint(
                    INVALID_DOC_ATTRIBUTES,
                    hir_id,
                    meta.span(),
                    errors::DocInlineOnlyUse {
                        attr_span: meta.span(),
                        item_span: (style == AttrStyle::Outer).then(|| self.tcx.hir_span(hir_id)),
                    },
                );
            }
        }
    }

    fn check_doc_masked(
        &self,
        style: AttrStyle,
        meta: &MetaItemInner,
        hir_id: HirId,
        target: Target,
    ) {
        if target != Target::ExternCrate {
            self.tcx.emit_node_span_lint(
                INVALID_DOC_ATTRIBUTES,
                hir_id,
                meta.span(),
                errors::DocMaskedOnlyExternCrate {
                    attr_span: meta.span(),
                    item_span: (style == AttrStyle::Outer).then(|| 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,
                meta.span(),
                errors::DocMaskedNotExternCrateSelf {
                    attr_span: meta.span(),
                    item_span: (style == AttrStyle::Outer).then(|| self.tcx.hir_span(hir_id)),
                },
            );
        }
    }

    /// Checks that an attribute is *not* used at the crate level. Returns `true` if valid.
    fn check_attr_not_crate_level(
        &self,
        meta: &MetaItemInner,
        hir_id: HirId,
        attr_name: &str,
    ) -> bool {
        if CRATE_HIR_ID == hir_id {
            self.dcx().emit_err(errors::DocAttrNotCrateLevel { span: meta.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,
        attr: &Attribute,
        style: AttrStyle,
        meta: &MetaItemInner,
        hir_id: HirId,
    ) -> bool {
        if hir_id != CRATE_HIR_ID {
            // insert a bang between `#` and `[...`
            let bang_span = attr.span().lo() + BytePos(1);
            let sugg = (style == AttrStyle::Outer
                && self.tcx.hir_get_parent_item(hir_id) == CRATE_OWNER_ID)
                .then_some(errors::AttrCrateLevelOnlySugg {
                    attr: attr.span().with_lo(bang_span).with_hi(bang_span),
                });
            self.tcx.emit_node_span_lint(
                INVALID_DOC_ATTRIBUTES,
                hir_id,
                meta.span(),
                errors::AttrCrateLevelOnly { sugg },
            );
            return false;
        }
        true
    }

    /// Checks that `doc(test(...))` attribute contains only valid attributes and are at the right place.
    fn check_test_attr(
        &self,
        attr: &Attribute,
        style: AttrStyle,
        meta: &MetaItemInner,
        hir_id: HirId,
    ) {
        if let Some(metas) = meta.meta_item_list() {
            for i_meta in metas {
                match (i_meta.name(), i_meta.meta_item()) {
                    (Some(sym::attr), _) => {
                        // Allowed everywhere like `#[doc]`
                    }
                    (Some(sym::no_crate_inject), _) => {
                        self.check_attr_crate_level(attr, style, meta, hir_id);
                    }
                    (_, Some(m)) => {
                        self.tcx.emit_node_span_lint(
                            INVALID_DOC_ATTRIBUTES,
                            hir_id,
                            i_meta.span(),
                            errors::DocTestUnknown {
                                path: rustc_ast_pretty::pprust::path_to_string(&m.path),
                            },
                        );
                    }
                    (_, None) => {
                        self.tcx.emit_node_span_lint(
                            INVALID_DOC_ATTRIBUTES,
                            hir_id,
                            i_meta.span(),
                            errors::DocTestLiteral,
                        );
                    }
                }
            }
        } else {
            self.tcx.emit_node_span_lint(
                INVALID_DOC_ATTRIBUTES,
                hir_id,
                meta.span(),
                errors::DocTestTakesList,
            );
        }
    }

    /// Check that the `#![doc(cfg_hide(...))]` attribute only contains a list of attributes.
    ///
    fn check_doc_cfg_hide(&self, meta: &MetaItemInner, hir_id: HirId) {
        if meta.meta_item_list().is_none() {
            self.tcx.emit_node_span_lint(
                INVALID_DOC_ATTRIBUTES,
                hir_id,
                meta.span(),
                errors::DocCfgHideTakesList,
            );
        }
    }

    /// 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: &Attribute,
        style: AttrStyle,
        hir_id: HirId,
        target: Target,
        specified_inline: &mut Option<(bool, Span)>,
        aliases: &mut FxHashMap<String, Span>,
    ) {
        if let Some(list) = attr.meta_item_list() {
            for meta in &list {
                if let Some(i_meta) = meta.meta_item() {
                    match i_meta.name() {
                        Some(sym::alias) => {
                            if self.check_attr_not_crate_level(meta, hir_id, "alias") {
                                self.check_doc_alias(meta, hir_id, target, aliases);
                            }
                        }

                        Some(sym::keyword) => {
                            if self.check_attr_not_crate_level(meta, hir_id, "keyword") {
                                self.check_doc_keyword(meta, hir_id);
                            }
                        }

                        Some(sym::fake_variadic) => {
                            if self.check_attr_not_crate_level(meta, hir_id, "fake_variadic") {
                                self.check_doc_fake_variadic(meta, hir_id);
                            }
                        }

                        Some(sym::search_unbox) => {
                            if self.check_attr_not_crate_level(meta, hir_id, "fake_variadic") {
                                self.check_doc_search_unbox(meta, hir_id);
                            }
                        }

                        Some(sym::test) => {
                            self.check_test_attr(attr, style, meta, hir_id);
                        }

                        Some(
                            sym::html_favicon_url
                            | sym::html_logo_url
                            | sym::html_playground_url
                            | sym::issue_tracker_base_url
                            | sym::html_root_url
                            | sym::html_no_source,
                        ) => {
                            self.check_attr_crate_level(attr, style, meta, hir_id);
                        }

                        Some(sym::cfg_hide) => {
                            if self.check_attr_crate_level(attr, style, meta, hir_id) {
                                self.check_doc_cfg_hide(meta, hir_id);
                            }
                        }

                        Some(sym::inline | sym::no_inline) => {
                            self.check_doc_inline(style, meta, hir_id, target, specified_inline)
                        }

                        Some(sym::masked) => self.check_doc_masked(style, meta, hir_id, target),

                        Some(sym::cfg | sym::hidden | sym::notable_trait) => {}

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

                        _ => {
                            let path = rustc_ast_pretty::pprust::path_to_string(&i_meta.path);
                            if i_meta.has_name(sym::spotlight) {
                                self.tcx.emit_node_span_lint(
                                    INVALID_DOC_ATTRIBUTES,
                                    hir_id,
                                    i_meta.span,
                                    errors::DocTestUnknownSpotlight { path, span: i_meta.span },
                                );
                            } else if i_meta.has_name(sym::include)
                                && let Some(value) = i_meta.value_str()
                            {
                                let applicability = if list.len() == 1 {
                                    Applicability::MachineApplicable
                                } else {
                                    Applicability::MaybeIncorrect
                                };
                                // If there are multiple attributes, the suggestion would suggest
                                // deleting all of them, which is incorrect.
                                self.tcx.emit_node_span_lint(
                                    INVALID_DOC_ATTRIBUTES,
                                    hir_id,
                                    i_meta.span,
                                    errors::DocTestUnknownInclude {
                                        path,
                                        value: value.to_string(),
                                        inner: match style {
                                            AttrStyle::Inner => "!",
                                            AttrStyle::Outer => "",
                                        },
                                        sugg: (attr.span(), applicability),
                                    },
                                );
                            } else if i_meta.has_name(sym::passes)
                                || i_meta.has_name(sym::no_default_passes)
                            {
                                self.tcx.emit_node_span_lint(
                                    INVALID_DOC_ATTRIBUTES,
                                    hir_id,
                                    i_meta.span,
                                    errors::DocTestUnknownPasses { path, span: i_meta.span },
                                );
                            } else if i_meta.has_name(sym::plugins) {
                                self.tcx.emit_node_span_lint(
                                    INVALID_DOC_ATTRIBUTES,
                                    hir_id,
                                    i_meta.span,
                                    errors::DocTestUnknownPlugins { path, span: i_meta.span },
                                );
                            } else {
                                self.tcx.emit_node_span_lint(
                                    INVALID_DOC_ATTRIBUTES,
                                    hir_id,
                                    i_meta.span,
                                    errors::DocTestUnknownAny { path },
                                );
                            }
                        }
                    }
                } else {
                    self.tcx.emit_node_span_lint(
                        INVALID_DOC_ATTRIBUTES,
                        hir_id,
                        meta.span(),
                        errors::DocInvalid,
                    );
                }
            }
        }
    }

    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 });
        }
    }

    /// Warns against some misuses of `#[must_use]`
    fn check_must_use(&self, hir_id: HirId, attr_span: Span, target: Target) {
        if matches!(
            target,
            Target::Fn
                | Target::Enum
                | Target::Struct
                | Target::Union
                | Target::Method(MethodKind::Trait { body: false } | MethodKind::Inherent)
                | Target::ForeignFn
                // `impl Trait` in return position can trip
                // `unused_must_use` if `Trait` is marked as
                // `#[must_use]`
                | Target::Trait
        ) {
            return;
        }

        // `#[must_use]` can be applied to a trait method definition with a default body
        if let Target::Method(MethodKind::Trait { body: true }) = target
            && 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)
            && let hir::ItemKind::Trait(..) = containing_item.kind
        {
            return;
        }

        self.tcx.emit_node_span_lint(
            UNUSED_ATTRIBUTES,
            hir_id,
            attr_span,
            errors::MustUseNoEffect { target: target.plural_name(), 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: &Attribute, 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(_) => {
                            self.dcx().emit_err(errors::ReprAlignShouldBeAlign {
                                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(),
            });
        }
        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 });
            }
            _ => {}
        }
    }

    /// Checks if the items on the `#[debugger_visualizer]` attribute are valid.
    fn check_debugger_visualizer(&self, attr: &Attribute, target: Target) {
        // Here we only check that the #[debugger_visualizer] attribute is attached
        // to nothing other than a module. All other checks are done in the
        // `debugger_visualizer` query where they need to be done for decoding
        // anyway.
        match target {
            Target::Mod => {}
            _ => {
                self.dcx().emit_err(errors::DebugVisualizerPlacement { span: attr.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: &Attribute, _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: &Attribute, target: Target) {
        if target != Target::MacroDef {
            self.tcx.emit_node_span_lint(
                UNUSED_ATTRIBUTES,
                hir_id,
                attr.span(),
                errors::MacroExport::Normal,
            );
        } else if let Some(meta_item_list) = attr.meta_item_list()
            && !meta_item_list.is_empty()
        {
            if meta_item_list.len() > 1 {
                self.tcx.emit_node_span_lint(
                    INVALID_MACRO_EXPORT_ARGUMENTS,
                    hir_id,
                    attr.span(),
                    errors::MacroExport::TooManyItems,
                );
            } else if !meta_item_list[0].has_name(sym::local_inner_macros) {
                self.tcx.emit_node_span_lint(
                    INVALID_MACRO_EXPORT_ARGUMENTS,
                    hir_id,
                    meta_item_list[0].span(),
                    errors::MacroExport::InvalidArgument,
                );
            }
        } else {
            // 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) => self.tcx.emit_node_span_lint(
                        UNUSED_ATTRIBUTES,
                        hir_id,
                        attr.span(),
                        errors::OuterCrateLevelAttr,
                    ),
                    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.select_where_possible();
        if !errors.is_empty() {
            return;
        }

        let expected_sig = tcx.mk_fn_sig(
            std::iter::repeat(token_stream).take(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.select_all_or_error();
        if !errors.is_empty() {
            infcx.err_ctxt().report_fulfillment_errors(errors);
            self.abort.set(true);
        }
    }

    fn check_type_const(&self, hir_id: HirId, attr_span: Span, target: Target) {
        let tcx = self.tcx;
        if target == Target::AssocConst
            && let parent = tcx.parent(hir_id.expect_owner().to_def_id())
            && self.tcx.def_kind(parent) == DefKind::Trait
        {
            return;
        } else {
            self.dcx()
                .struct_span_err(
                    attr_span,
                    "`#[type_const]` must only be applied to trait associated constants",
                )
                .emit();
        }
    }

    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 });
        };
    }
}

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 && !self.tcx.has_attr(def_id, sym::macro_export) {
                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)))
            .filter(|attr| !attr.is_parsed_attr())
            .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::macro_export,
        sym::rustc_main,
        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: &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
        })
}