rustc_attr_parsing/attributes/

rustc_internal.rs

use std::path::PathBuf;

use rustc_ast::{LitIntType, LitKind, MetaItemLit};
use rustc_feature::AttributeStability;
use rustc_hir::LangItem;
use rustc_hir::attrs::{
    BorrowckGraphvizFormatKind, CguFields, CguKind, DivergingBlockBehavior,
    DivergingFallbackBehavior, RustcCleanAttribute, RustcCleanQueries, RustcMirKind,
};
use rustc_span::Symbol;

use super::prelude::*;
use super::util::parse_single_integer;
use crate::diagnostics;
use crate::diagnostics::UnknownExternLangItem;
use crate::session_diagnostics::{
    AttributeRequiresOpt, CguFieldsMissing, RustcScalableVectorCountOutOfRange, UnknownLangItem,
};

pub(crate) struct RustcMainParser;

impl NoArgsAttributeParser for RustcMainParser {
    const PATH: &[Symbol] = &[sym::rustc_main];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
    const STABILITY: AttributeStability = unstable!(
        rustc_attrs,
        "the `#[rustc_main]` attribute is used internally to specify test entry point function"
    );
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcMain;
}

pub(crate) struct RustcMustImplementOneOfParser;

impl SingleAttributeParser for RustcMustImplementOneOfParser {
    const PATH: &[Symbol] = &[sym::rustc_must_implement_one_of];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
    const STABILITY: AttributeStability = unstable!(
        rustc_attrs,
        "the `#[rustc_must_implement_one_of]` attribute is used to change minimal complete definition of a trait. Its syntax and semantics are highly experimental and will be subject to change before stabilization"
    );
    const TEMPLATE: AttributeTemplate = template!(List: &["function1, function2, ..."]);
    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        let list = cx.expect_list(args, cx.attr_span)?;

        let mut fn_names = ThinVec::new();

        let inputs: Vec<_> = list.mixed().collect();

        if inputs.len() < 2 {
            cx.adcx().expected_list_with_num_args_or_more(2, list.span);
            return None;
        }

        let mut errored = false;
        for argument in inputs {
            let Some(meta) = argument.meta_item_no_args() else {
                cx.adcx().expected_identifier(argument.span());
                return None;
            };

            let Some(ident) = meta.ident() else {
                cx.dcx()
                    .emit_err(diagnostics::MustBeNameOfAssociatedFunction { span: meta.span() });
                errored = true;
                continue;
            };

            fn_names.push(ident);
        }
        if errored {
            return None;
        }

        Some(AttributeKind::RustcMustImplementOneOf { attr_span: cx.attr_span, fn_names })
    }
}

pub(crate) struct RustcNeverReturnsNullPtrParser;

impl NoArgsAttributeParser for RustcNeverReturnsNullPtrParser {
    const PATH: &[Symbol] = &[sym::rustc_never_returns_null_ptr];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);

    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcNeverReturnsNullPtr;
}
pub(crate) struct RustcNoImplicitAutorefsParser;

impl NoArgsAttributeParser for RustcNoImplicitAutorefsParser {
    const PATH: &[Symbol] = &[sym::rustc_no_implicit_autorefs];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);

    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcNoImplicitAutorefs;
}

pub(crate) struct RustcLegacyConstGenericsParser;

impl SingleAttributeParser for RustcLegacyConstGenericsParser {
    const PATH: &[Symbol] = &[sym::rustc_legacy_const_generics];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
    const TEMPLATE: AttributeTemplate = template!(List: &["N"]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        let meta_items = cx.expect_list(args, cx.attr_span)?;

        let mut parsed_indexes = ThinVec::new();
        let mut errored = false;

        for possible_index in meta_items.mixed() {
            if let MetaItemOrLitParser::Lit(MetaItemLit {
                kind: LitKind::Int(index, LitIntType::Unsuffixed),
                ..
            }) = possible_index
            {
                parsed_indexes.push((index.0 as usize, possible_index.span()));
            } else {
                cx.adcx().expected_integer_literal(possible_index.span());
                errored = true;
            }
        }
        if errored {
            return None;
        } else if parsed_indexes.is_empty() {
            cx.adcx().expected_at_least_one_argument(args.span()?);
            return None;
        }

        Some(AttributeKind::RustcLegacyConstGenerics {
            fn_indexes: parsed_indexes,
            attr_span: cx.attr_span,
        })
    }
}

pub(crate) struct RustcInheritOverflowChecksParser;

impl NoArgsAttributeParser for RustcInheritOverflowChecksParser {
    const PATH: &[Symbol] = &[sym::rustc_inherit_overflow_checks];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Closure),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcInheritOverflowChecks;
}

pub(crate) struct RustcLintOptDenyFieldAccessParser;

impl SingleAttributeParser for RustcLintOptDenyFieldAccessParser {
    const PATH: &[Symbol] = &[sym::rustc_lint_opt_deny_field_access];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Field)]);
    const TEMPLATE: AttributeTemplate = template!(Word);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        let arg = cx.expect_single_element_list(args, cx.attr_span)?;
        let lint_message = cx.expect_string_literal(arg)?;

        Some(AttributeKind::RustcLintOptDenyFieldAccess { lint_message })
    }
}

pub(crate) struct RustcLintOptTyParser;

impl NoArgsAttributeParser for RustcLintOptTyParser {
    const PATH: &[Symbol] = &[sym::rustc_lint_opt_ty];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Struct)]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcLintOptTy;
}

fn parse_cgu_fields(
    cx: &mut AcceptContext<'_, '_>,
    args: &ArgParser,
    accepts_kind: bool,
) -> Option<(Symbol, Symbol, Option<CguKind>)> {
    let args = cx.expect_list(args, cx.attr_span)?;

    let mut cfg = None::<(Symbol, Span)>;
    let mut module = None::<(Symbol, Span)>;
    let mut kind = None::<(Symbol, Span)>;

    for arg in args.mixed() {
        let Some((ident, arg)) = cx.expect_name_value(arg, arg.span(), None) else {
            continue;
        };

        let res = match ident.name {
            sym::cfg => &mut cfg,
            sym::module => &mut module,
            sym::kind if accepts_kind => &mut kind,
            _ => {
                cx.adcx().expected_specific_argument(
                    ident.span,
                    if accepts_kind {
                        &[sym::cfg, sym::module, sym::kind]
                    } else {
                        &[sym::cfg, sym::module]
                    },
                );
                continue;
            }
        };

        let str = cx.expect_string_literal(arg)?;

        if res.is_some() {
            cx.adcx().duplicate_key(ident.span.to(arg.args_span()), ident.name);
            continue;
        }

        *res = Some((str, arg.value_span));
    }

    let Some((cfg, _)) = cfg else {
        cx.emit_err(CguFieldsMissing { span: args.span, name: &cx.attr_path, field: sym::cfg });
        return None;
    };
    let Some((module, _)) = module else {
        cx.emit_err(CguFieldsMissing { span: args.span, name: &cx.attr_path, field: sym::module });
        return None;
    };
    let kind = if let Some((kind, span)) = kind {
        Some(match kind {
            sym::no => CguKind::No,
            sym::pre_dash_lto => CguKind::PreDashLto,
            sym::post_dash_lto => CguKind::PostDashLto,
            sym::any => CguKind::Any,
            _ => {
                cx.adcx().expected_specific_argument_strings(
                    span,
                    &[sym::no, sym::pre_dash_lto, sym::post_dash_lto, sym::any],
                );
                return None;
            }
        })
    } else {
        // return None so that an unwrap for the attributes that need it is ok.
        if accepts_kind {
            cx.emit_err(CguFieldsMissing {
                span: args.span,
                name: &cx.attr_path,
                field: sym::kind,
            });
            return None;
        };

        None
    };

    Some((cfg, module, kind))
}

#[derive(Default)]
pub(crate) struct RustcCguTestAttributeParser {
    items: ThinVec<(Span, CguFields)>,
}

impl AttributeParser for RustcCguTestAttributeParser {
    const ATTRIBUTES: AcceptMapping<Self> = &[
        (
            &[sym::rustc_partition_reused],
            template!(List: &[r#"cfg = "...", module = "...""#]),
            unstable!(rustc_attrs),
            |this, cx, args| {
                this.items.extend(parse_cgu_fields(cx, args, false).map(|(cfg, module, _)| {
                    (cx.attr_span, CguFields::PartitionReused { cfg, module })
                }));
            },
        ),
        (
            &[sym::rustc_partition_codegened],
            template!(List: &[r#"cfg = "...", module = "...""#]),
            unstable!(rustc_attrs),
            |this, cx, args| {
                this.items.extend(parse_cgu_fields(cx, args, false).map(|(cfg, module, _)| {
                    (cx.attr_span, CguFields::PartitionCodegened { cfg, module })
                }));
            },
        ),
        (
            &[sym::rustc_expected_cgu_reuse],
            template!(List: &[r#"cfg = "...", module = "...", kind = "...""#]),
            unstable!(rustc_attrs),
            |this, cx, args| {
                this.items.extend(parse_cgu_fields(cx, args, true).map(|(cfg, module, kind)| {
                    // unwrap ok because if not given, we return None in `parse_cgu_fields`.
                    (cx.attr_span, CguFields::ExpectedCguReuse { cfg, module, kind: kind.unwrap() })
                }));
            },
        ),
    ];

    const ALLOWED_TARGETS: AllowedTargets<'_> =
        AllowedTargets::AllowList(&[Allow(Target::Mod), Allow(Target::Crate)]);

    fn finalize(self, _cx: &FinalizeContext<'_, '_>) -> Option<AttributeKind> {
        Some(AttributeKind::RustcCguTestAttr(self.items))
    }
}

pub(crate) struct RustcDeprecatedSafe2024Parser;

impl SingleAttributeParser for RustcDeprecatedSafe2024Parser {
    const PATH: &[Symbol] = &[sym::rustc_deprecated_safe_2024];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
    ]);
    const TEMPLATE: AttributeTemplate = template!(List: &[r#"audit_that = "...""#]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        let single = cx.expect_single_element_list(args, cx.attr_span)?;

        let (path, arg) = cx.expect_name_value(single, cx.attr_span, None)?;

        if path.name != sym::audit_that {
            cx.adcx().expected_specific_argument(path.span, &[sym::audit_that]);
            return None;
        };

        let suggestion = cx.expect_string_literal(arg)?;

        Some(AttributeKind::RustcDeprecatedSafe2024 { suggestion })
    }
}

pub(crate) struct RustcConversionSuggestionParser;

impl NoArgsAttributeParser for RustcConversionSuggestionParser {
    const PATH: &[Symbol] = &[sym::rustc_conversion_suggestion];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcConversionSuggestion;
}

pub(crate) struct RustcCaptureAnalysisParser;

impl NoArgsAttributeParser for RustcCaptureAnalysisParser {
    const PATH: &[Symbol] = &[sym::rustc_capture_analysis];
    const ALLOWED_TARGETS: AllowedTargets<'_> =
        AllowedTargets::AllowList(&[Allow(Target::Closure)]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcCaptureAnalysis;
}

pub(crate) struct RustcNeverTypeOptionsParser;

impl SingleAttributeParser for RustcNeverTypeOptionsParser {
    const PATH: &[Symbol] = &[sym::rustc_never_type_options];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Crate)]);
    const TEMPLATE: AttributeTemplate = template!(List: &[
        r#"fallback = "unit", "never", "no""#,
        r#"diverging_block_default = "unit", "never""#,
    ]);
    const STABILITY: AttributeStability = unstable!(
        rustc_attrs,
        "`rustc_never_type_options` is used to experiment with never type fallback and work on never type stabilization"
    );

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        let list = cx.expect_list(args, cx.attr_span)?;

        let mut fallback = None::<Ident>;
        let mut diverging_block_default = None::<Ident>;

        for arg in list.mixed() {
            let Some((ident, arg)) = cx.expect_name_value(arg, arg.span(), None) else {
                continue;
            };

            let res = match ident.name {
                sym::fallback => &mut fallback,
                sym::diverging_block_default => &mut diverging_block_default,
                _ => {
                    cx.adcx().expected_specific_argument(
                        ident.span,
                        &[sym::fallback, sym::diverging_block_default],
                    );
                    continue;
                }
            };

            let field = cx.expect_string_literal(arg)?;

            if res.is_some() {
                cx.adcx().duplicate_key(ident.span, ident.name);
                continue;
            }

            *res = Some(Ident { name: field, span: arg.value_span });
        }

        let fallback = match fallback {
            None => None,
            Some(Ident { name: sym::unit, .. }) => Some(DivergingFallbackBehavior::ToUnit),
            Some(Ident { name: sym::never, .. }) => Some(DivergingFallbackBehavior::ToNever),
            Some(Ident { name: sym::no, .. }) => Some(DivergingFallbackBehavior::NoFallback),
            Some(Ident { span, .. }) => {
                cx.adcx()
                    .expected_specific_argument_strings(span, &[sym::unit, sym::never, sym::no]);
                return None;
            }
        };

        let diverging_block_default = match diverging_block_default {
            None => None,
            Some(Ident { name: sym::unit, .. }) => Some(DivergingBlockBehavior::Unit),
            Some(Ident { name: sym::never, .. }) => Some(DivergingBlockBehavior::Never),
            Some(Ident { span, .. }) => {
                cx.adcx().expected_specific_argument_strings(span, &[sym::unit, sym::no]);
                return None;
            }
        };

        Some(AttributeKind::RustcNeverTypeOptions { fallback, diverging_block_default })
    }
}

pub(crate) struct RustcTrivialFieldReadsParser;

impl NoArgsAttributeParser for RustcTrivialFieldReadsParser {
    const PATH: &[Symbol] = &[sym::rustc_trivial_field_reads];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcTrivialFieldReads;
}

pub(crate) struct RustcNoMirInlineParser;

impl NoArgsAttributeParser for RustcNoMirInlineParser {
    const PATH: &[Symbol] = &[sym::rustc_no_mir_inline];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcNoMirInline;
}

pub(crate) struct RustcNoWritableParser;

impl NoArgsAttributeParser for RustcNoWritableParser {
    const PATH: &[Symbol] = &[sym::rustc_no_writable];
    const ON_DUPLICATE: OnDuplicate = OnDuplicate::Error;
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Closure),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Method(MethodKind::Trait { body: true })),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcNoWritable;
}

pub(crate) struct RustcLintQueryInstabilityParser;

impl NoArgsAttributeParser for RustcLintQueryInstabilityParser {
    const PATH: &[Symbol] = &[sym::rustc_lint_query_instability];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcLintQueryInstability;
}

pub(crate) struct RustcRegionsParser;

impl NoArgsAttributeParser for RustcRegionsParser {
    const PATH: &[Symbol] = &[sym::rustc_regions];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcRegions;
}

pub(crate) struct RustcLintUntrackedQueryInformationParser;

impl NoArgsAttributeParser for RustcLintUntrackedQueryInformationParser {
    const PATH: &[Symbol] = &[sym::rustc_lint_untracked_query_information];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcLintUntrackedQueryInformation;
}

pub(crate) struct RustcSimdMonomorphizeLaneLimitParser;

impl SingleAttributeParser for RustcSimdMonomorphizeLaneLimitParser {
    const PATH: &[Symbol] = &[sym::rustc_simd_monomorphize_lane_limit];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Struct)]);
    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "N");
    const STABILITY: AttributeStability = unstable!(rustc_attrs);

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        let nv = cx.expect_name_value(args, cx.attr_span, None)?;
        Some(AttributeKind::RustcSimdMonomorphizeLaneLimit(cx.parse_limit_int(nv)?))
    }
}

pub(crate) struct RustcScalableVectorParser;

impl SingleAttributeParser for RustcScalableVectorParser {
    const PATH: &[Symbol] = &[sym::rustc_scalable_vector];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Struct)]);
    const TEMPLATE: AttributeTemplate = template!(Word, List: &["count"]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        if args.as_no_args().is_ok() {
            return Some(AttributeKind::RustcScalableVector { element_count: None });
        }

        let n = parse_single_integer(cx, args)?;
        let Ok(n) = n.try_into() else {
            cx.emit_err(RustcScalableVectorCountOutOfRange { span: cx.attr_span, n });
            return None;
        };
        Some(AttributeKind::RustcScalableVector { element_count: Some(n) })
    }
}

pub(crate) struct LangParser;

impl SingleAttributeParser for LangParser {
    const PATH: &[Symbol] = &[sym::lang];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::ManuallyChecked;
    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "name");
    const STABILITY: AttributeStability = unstable!(lang_items);

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        let nv = cx.expect_name_value(args, cx.attr_span, None)?;
        let name = cx.expect_string_literal(nv)?;
        let Some(lang_item) = LangItem::from_name(name) else {
            cx.emit_err(UnknownLangItem { span: cx.attr_span, name });
            return None;
        };

        // Only weak lang items may be applied to foreign items
        if [Target::ForeignFn, Target::ForeignStatic, Target::ForeignTy, Target::ForeignMod]
            .contains(&cx.target)
            && !lang_item.is_weak()
        {
            cx.emit_err(UnknownExternLangItem { span: cx.attr_span, lang_item: lang_item.name() });
            return None;
        }

        // Check the target
        let allowed_targets: &[_] = if lang_item == LangItem::PanicImpl {
            &[Allow(Target::Fn), Allow(Target::ForeignFn)]
        } else {
            &[Allow(lang_item.target())]
        };
        cx.check_target(&format!(" = \"{name}\""), &AllowedTargets::AllowList(allowed_targets));

        Some(AttributeKind::Lang(lang_item))
    }
}

pub(crate) struct RustcHasIncoherentInherentImplsParser;

impl NoArgsAttributeParser for RustcHasIncoherentInherentImplsParser {
    const PATH: &[Symbol] = &[sym::rustc_has_incoherent_inherent_impls];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Trait),
        Allow(Target::Struct),
        Allow(Target::Enum),
        Allow(Target::Union),
        Allow(Target::ForeignTy),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcHasIncoherentInherentImpls;
}

pub(crate) struct PanicHandlerParser;

impl NoArgsAttributeParser for PanicHandlerParser {
    const PATH: &[Symbol] = &[sym::panic_handler];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
    const STABILITY: AttributeStability = AttributeStability::Stable;
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Lang(LangItem::PanicImpl);
}

pub(crate) struct RustcNounwindParser;

impl NoArgsAttributeParser for RustcNounwindParser {
    const PATH: &[Symbol] = &[sym::rustc_nounwind];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::ForeignFn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Method(MethodKind::Trait { body: true })),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcNounwind;
}

pub(crate) struct RustcOffloadKernelParser;

impl NoArgsAttributeParser for RustcOffloadKernelParser {
    const PATH: &[Symbol] = &[sym::rustc_offload_kernel];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcOffloadKernel;
}

pub(crate) struct RustcMirParser;

impl CombineAttributeParser for RustcMirParser {
    const PATH: &[Symbol] = &[sym::rustc_mir];

    type Item = RustcMirKind;

    const CONVERT: ConvertFn<Self::Item> = |items, _| AttributeKind::RustcMir(items);
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
    ]);
    const TEMPLATE: AttributeTemplate = template!(List: &["arg1, arg2, ..."]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);

    fn extend(
        cx: &mut AcceptContext<'_, '_>,
        args: &ArgParser,
    ) -> impl IntoIterator<Item = Self::Item> {
        let Some(list) = cx.expect_list(args, cx.attr_span) else {
            return ThinVec::new();
        };

        list.mixed()
            .filter_map(|arg| arg.meta_item())
            .filter_map(|mi| {
                if let Some(ident) = mi.ident() {
                    match ident.name {
                        sym::rustc_peek_maybe_init => Some(RustcMirKind::PeekMaybeInit),
                        sym::rustc_peek_maybe_uninit => Some(RustcMirKind::PeekMaybeUninit),
                        sym::rustc_peek_liveness => Some(RustcMirKind::PeekLiveness),
                        sym::stop_after_dataflow => Some(RustcMirKind::StopAfterDataflow),
                        sym::borrowck_graphviz_postflow => {
                            let nv = cx.expect_name_value(
                                mi.args(),
                                mi.span(),
                                Some(sym::borrowck_graphviz_postflow),
                            )?;
                            let path = cx.expect_string_literal(nv)?;
                            let path = PathBuf::from(path.to_string());
                            if path.file_name().is_some() {
                                Some(RustcMirKind::BorrowckGraphvizPostflow { path })
                            } else {
                                cx.adcx().expected_filename_literal(nv.value_span);
                                None
                            }
                        }
                        sym::borrowck_graphviz_format => {
                            let nv = cx.expect_name_value(
                                mi.args(),
                                mi.span(),
                                Some(sym::borrowck_graphviz_format),
                            )?;
                            let Some(format) = nv.value_as_ident() else {
                                cx.adcx().expected_identifier(nv.value_span);
                                return None;
                            };
                            match format.name {
                                sym::two_phase => Some(RustcMirKind::BorrowckGraphvizFormat {
                                    format: BorrowckGraphvizFormatKind::TwoPhase,
                                }),
                                _ => {
                                    cx.adcx()
                                        .expected_specific_argument(format.span, &[sym::two_phase]);
                                    None
                                }
                            }
                        }
                        _ => None,
                    }
                } else {
                    None
                }
            })
            .collect()
    }
}
pub(crate) struct RustcNonConstTraitMethodParser;

impl NoArgsAttributeParser for RustcNonConstTraitMethodParser {
    const PATH: &[Symbol] = &[sym::rustc_non_const_trait_method];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::Trait { body: false })),
    ]);
    const STABILITY: AttributeStability = unstable!(
        rustc_attrs,
        "`#[rustc_non_const_trait_method]` should only used by the standard library to mark trait methods as non-const to allow large traits an easier transition to const"
    );
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcNonConstTraitMethod;
}

pub(crate) struct RustcCleanParser;

impl CombineAttributeParser for RustcCleanParser {
    const PATH: &[Symbol] = &[sym::rustc_clean];

    type Item = RustcCleanAttribute;

    const CONVERT: ConvertFn<Self::Item> = |items, _| AttributeKind::RustcClean(items);
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        // tidy-alphabetical-start
        Allow(Target::AssocConst),
        Allow(Target::AssocTy),
        Allow(Target::Const),
        Allow(Target::Enum),
        Allow(Target::Expression),
        Allow(Target::Field),
        Allow(Target::Fn),
        Allow(Target::ForeignMod),
        Allow(Target::Impl { of_trait: false }),
        Allow(Target::Impl { of_trait: true }),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Mod),
        Allow(Target::Static),
        Allow(Target::Struct),
        Allow(Target::Trait),
        Allow(Target::TyAlias),
        Allow(Target::Union),
        // tidy-alphabetical-end
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const TEMPLATE: AttributeTemplate =
        template!(List: &[r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#]);

    fn extend(
        cx: &mut AcceptContext<'_, '_>,
        args: &ArgParser,
    ) -> impl IntoIterator<Item = Self::Item> {
        if !cx.cx.sess.opts.unstable_opts.query_dep_graph {
            cx.emit_err(AttributeRequiresOpt { span: cx.attr_span, opt: "-Z query-dep-graph" });
        }
        let list = cx.expect_list(args, cx.attr_span)?;

        let mut except = None;
        let mut loaded_from_disk = None;
        let mut cfg = None;

        for item in list.mixed() {
            let Some((ident, value)) = cx.expect_name_value(item, item.span(), None) else {
                continue;
            };
            let value_span = value.value_span;
            let Some(value) = cx.expect_string_literal(value) else {
                continue;
            };
            match ident.name {
                sym::cfg if cfg.is_some() => {
                    cx.adcx().duplicate_key(item.span(), sym::cfg);
                }
                sym::cfg => {
                    cfg = Some(value);
                }
                sym::except if except.is_some() => {
                    cx.adcx().duplicate_key(item.span(), sym::except);
                }
                sym::except => {
                    let entries =
                        value.as_str().split(',').map(|s| Symbol::intern(s.trim())).collect();
                    except = Some(RustcCleanQueries { entries, span: value_span });
                }
                sym::loaded_from_disk if loaded_from_disk.is_some() => {
                    cx.adcx().duplicate_key(item.span(), sym::loaded_from_disk);
                }
                sym::loaded_from_disk => {
                    let entries =
                        value.as_str().split(',').map(|s| Symbol::intern(s.trim())).collect();
                    loaded_from_disk = Some(RustcCleanQueries { entries, span: value_span });
                }
                _ => {
                    cx.adcx().expected_specific_argument(
                        ident.span,
                        &[sym::cfg, sym::except, sym::loaded_from_disk],
                    );
                }
            }
        }
        let Some(cfg) = cfg else {
            cx.adcx().expected_specific_argument(list.span, &[sym::cfg]);
            return None;
        };

        Some(RustcCleanAttribute { span: cx.attr_span, cfg, except, loaded_from_disk })
    }
}

pub(crate) struct RustcIfThisChangedParser;

impl SingleAttributeParser for RustcIfThisChangedParser {
    const PATH: &[Symbol] = &[sym::rustc_if_this_changed];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        // tidy-alphabetical-start
        Allow(Target::AssocConst),
        Allow(Target::AssocTy),
        Allow(Target::Const),
        Allow(Target::Enum),
        Allow(Target::Expression),
        Allow(Target::Field),
        Allow(Target::Fn),
        Allow(Target::ForeignMod),
        Allow(Target::Impl { of_trait: false }),
        Allow(Target::Impl { of_trait: true }),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Mod),
        Allow(Target::Static),
        Allow(Target::Struct),
        Allow(Target::Trait),
        Allow(Target::TyAlias),
        Allow(Target::Union),
        // tidy-alphabetical-end
    ]);
    const TEMPLATE: AttributeTemplate = template!(Word, List: &["DepNode"]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        if !cx.cx.sess.opts.unstable_opts.query_dep_graph {
            cx.emit_err(AttributeRequiresOpt { span: cx.attr_span, opt: "-Z query-dep-graph" });
        }
        match args {
            ArgParser::NoArgs => Some(AttributeKind::RustcIfThisChanged(cx.attr_span, None)),
            ArgParser::List(list) => {
                let item = cx.expect_single(list)?;
                let Some(ident) = item.meta_item_no_args().and_then(|item| item.ident()) else {
                    cx.adcx().expected_identifier(item.span());
                    return None;
                };
                Some(AttributeKind::RustcIfThisChanged(cx.attr_span, Some(ident.name)))
            }
            ArgParser::NameValue(_) => {
                let inner_span = cx.inner_span;
                cx.adcx().expected_list_or_no_args(inner_span);
                None
            }
        }
    }
}

pub(crate) struct RustcThenThisWouldNeedParser;

impl CombineAttributeParser for RustcThenThisWouldNeedParser {
    const PATH: &[Symbol] = &[sym::rustc_then_this_would_need];
    type Item = Ident;

    const CONVERT: ConvertFn<Self::Item> =
        |items, _span| AttributeKind::RustcThenThisWouldNeed(items);
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        // tidy-alphabetical-start
        Allow(Target::AssocConst),
        Allow(Target::AssocTy),
        Allow(Target::Const),
        Allow(Target::Enum),
        Allow(Target::Expression),
        Allow(Target::Field),
        Allow(Target::Fn),
        Allow(Target::ForeignMod),
        Allow(Target::Impl { of_trait: false }),
        Allow(Target::Impl { of_trait: true }),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Mod),
        Allow(Target::Static),
        Allow(Target::Struct),
        Allow(Target::Trait),
        Allow(Target::TyAlias),
        Allow(Target::Union),
        // tidy-alphabetical-end
    ]);
    const TEMPLATE: AttributeTemplate = template!(List: &["DepNode"]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);

    fn extend(
        cx: &mut AcceptContext<'_, '_>,
        args: &ArgParser,
    ) -> impl IntoIterator<Item = Self::Item> {
        if !cx.cx.sess.opts.unstable_opts.query_dep_graph {
            cx.emit_err(AttributeRequiresOpt { span: cx.attr_span, opt: "-Z query-dep-graph" });
        }
        let item = cx.expect_single_element_list(args, cx.attr_span)?;
        let Some(ident) = item.meta_item_no_args().and_then(|item| item.ident()) else {
            cx.adcx().expected_identifier(item.span());
            return None;
        };
        Some(ident)
    }
}

pub(crate) struct RustcInsignificantDtorParser;

impl NoArgsAttributeParser for RustcInsignificantDtorParser {
    const PATH: &[Symbol] = &[sym::rustc_insignificant_dtor];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Enum),
        Allow(Target::Struct),
        Allow(Target::ForeignTy),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcInsignificantDtor;
}

pub(crate) struct RustcEffectiveVisibilityParser;

impl NoArgsAttributeParser for RustcEffectiveVisibilityParser {
    const PATH: &[Symbol] = &[sym::rustc_effective_visibility];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Use),
        Allow(Target::Static),
        Allow(Target::Const),
        Allow(Target::Fn),
        Allow(Target::Closure),
        Allow(Target::Mod),
        Allow(Target::ForeignMod),
        Allow(Target::TyAlias),
        Allow(Target::Enum),
        Allow(Target::Variant),
        Allow(Target::Struct),
        Allow(Target::Field),
        Allow(Target::Union),
        Allow(Target::Trait),
        Allow(Target::TraitAlias),
        Allow(Target::Impl { of_trait: false }),
        Allow(Target::Impl { of_trait: true }),
        Allow(Target::AssocConst),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::AssocTy),
        Allow(Target::ForeignFn),
        Allow(Target::ForeignStatic),
        Allow(Target::ForeignTy),
        Allow(Target::MacroDef),
        Allow(Target::PatField),
        Allow(Target::Crate),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcEffectiveVisibility;
}

pub(crate) struct RustcDiagnosticItemParser;

impl SingleAttributeParser for RustcDiagnosticItemParser {
    const PATH: &[Symbol] = &[sym::rustc_diagnostic_item];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Trait),
        Allow(Target::Struct),
        Allow(Target::Enum),
        Allow(Target::MacroDef),
        Allow(Target::TyAlias),
        Allow(Target::AssocTy),
        Allow(Target::AssocConst),
        Allow(Target::Fn),
        Allow(Target::Const),
        Allow(Target::Mod),
        Allow(Target::Impl { of_trait: false }),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Crate),
    ]);
    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "name");
    const STABILITY: AttributeStability = unstable!(
        rustc_attrs,
        "the `#[rustc_diagnostic_item]` attribute allows the compiler to reference types from the standard library for diagnostic purposes"
    );

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        let nv = cx.expect_name_value(args, cx.attr_span, None)?;
        let value = cx.expect_string_literal(nv)?;
        Some(AttributeKind::RustcDiagnosticItem(value))
    }
}

pub(crate) struct RustcDoNotConstCheckParser;

impl NoArgsAttributeParser for RustcDoNotConstCheckParser {
    const PATH: &[Symbol] = &[sym::rustc_do_not_const_check];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Method(MethodKind::Trait { body: false })),
        Allow(Target::Method(MethodKind::Trait { body: true })),
    ]);
    const STABILITY: AttributeStability = unstable!(
        rustc_attrs,
        "`#[rustc_do_not_const_check]` skips const-check for this function's body"
    );
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcDoNotConstCheck;
}

pub(crate) struct RustcNonnullOptimizationGuaranteedParser;

impl NoArgsAttributeParser for RustcNonnullOptimizationGuaranteedParser {
    const PATH: &[Symbol] = &[sym::rustc_nonnull_optimization_guaranteed];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Struct)]);
    const STABILITY: AttributeStability = unstable!(
        rustc_attrs,
        "the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to document guaranteed niche optimizations in the standard library",
        "the compiler does not even check whether the type indeed is being non-null-optimized; it is your responsibility to ensure that the attribute is only used on types that are optimized"
    );
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcNonnullOptimizationGuaranteed;
}

pub(crate) struct RustcStrictCoherenceParser;

impl NoArgsAttributeParser for RustcStrictCoherenceParser {
    const PATH: &[Symbol] = &[sym::rustc_strict_coherence];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Trait),
        Allow(Target::Struct),
        Allow(Target::Enum),
        Allow(Target::Union),
        Allow(Target::ForeignTy),
    ]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = AttributeKind::RustcStrictCoherence;
}

pub(crate) struct RustcReservationImplParser;

impl SingleAttributeParser for RustcReservationImplParser {
    const PATH: &[Symbol] = &[sym::rustc_reservation_impl];
    const ALLOWED_TARGETS: AllowedTargets<'_> =
        AllowedTargets::AllowList(&[Allow(Target::Impl { of_trait: true })]);
    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "reservation message");
    const STABILITY: AttributeStability = unstable!(rustc_attrs);

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        let nv = cx.expect_name_value(args, cx.attr_span, None)?;
        let value_str = cx.expect_string_literal(nv)?;

        Some(AttributeKind::RustcReservationImpl(value_str))
    }
}

pub(crate) struct PreludeImportParser;

impl NoArgsAttributeParser for PreludeImportParser {
    const PATH: &[Symbol] = &[sym::prelude_import];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Use)]);
    const STABILITY: AttributeStability = unstable!(prelude_import);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::PreludeImport;
}

pub(crate) struct RustcDocPrimitiveParser;

impl SingleAttributeParser for RustcDocPrimitiveParser {
    const PATH: &[Symbol] = &[sym::rustc_doc_primitive];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Mod)]);
    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "primitive name");
    const STABILITY: AttributeStability = unstable!(
        rustc_attrs,
        "the `#[rustc_doc_primitive]` attribute is used by the standard library to provide a way to generate documentation for primitive types"
    );

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        let nv = cx.expect_name_value(args, cx.attr_span, None)?;
        let value_str = cx.expect_string_literal(nv)?;

        Some(AttributeKind::RustcDocPrimitive(cx.attr_span, value_str))
    }
}

pub(crate) struct RustcIntrinsicParser;

impl NoArgsAttributeParser for RustcIntrinsicParser {
    const PATH: &[Symbol] = &[sym::rustc_intrinsic];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
    const STABILITY: AttributeStability = unstable!(intrinsics);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcIntrinsic;
}

pub(crate) struct RustcIntrinsicConstStableIndirectParser;

impl NoArgsAttributeParser for RustcIntrinsicConstStableIndirectParser {
    const PATH: &'static [Symbol] = &[sym::rustc_intrinsic_const_stable_indirect];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcIntrinsicConstStableIndirect;
}

pub(crate) struct RustcExhaustiveParser;

impl NoArgsAttributeParser for RustcExhaustiveParser {
    const PATH: &'static [Symbol] = &[sym::rustc_must_match_exhaustively];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Enum)]);
    const STABILITY: AttributeStability = unstable!(rustc_attrs);
    const CREATE: fn(Span) -> AttributeKind = AttributeKind::RustcMustMatchExhaustively;
}