rustc_attr_parsing/attributes/

codegen_attrs.rs

use rustc_attr_ir::{
    CoverageAttrKind, InstrumentFnAttr, OptimizeAttr, RtsanSetting, UsedBy, find_attr,
};
use rustc_feature::AttributeStability;
use rustc_session::diagnostics::feature_err;
use rustc_span::edition::Edition::Edition2024;
use rustc_structures::SanitizerSet;

use super::prelude::*;
use crate::attributes::AttributeSafety;
use crate::diagnostics::{
    EmptyExportName, EmptySection, NakedFunctionIncompatibleAttribute, NullOnExport,
    NullOnObjcClass, NullOnObjcSelector, NullOnSection, ObjcClassExpectedStringLiteral,
    ObjcSelectorExpectedStringLiteral, SanitizeInvalidStatic, TargetFeatureOnLangItem,
    TrackCallerOnLangItem,
};
use crate::target_checking::Policy::AllowSilent;

pub(crate) struct OptimizeParser;

impl SingleAttributeParser for OptimizeParser {
    const PATH: &[Symbol] = &[sym::optimize];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Closure),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Method(MethodKind::Inherent)),
    ]);
    const TEMPLATE: AttributeTemplate = template!(List: &["size", "speed", "none"]);
    const STABILITY: AttributeStability = unstable!(optimize_attribute);

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

        let res = match single.meta_item_no_args().and_then(|i| i.path().word().map(|i| i.name)) {
            Some(sym::size) => OptimizeAttr::Size,
            Some(sym::speed) => OptimizeAttr::Speed,
            Some(sym::none) => OptimizeAttr::DoNotOptimize,
            _ => {
                cx.adcx()
                    .expected_specific_argument(single.span(), &[sym::size, sym::speed, sym::none]);
                OptimizeAttr::Default
            }
        };

        Some(AttributeKind::Optimize(res, cx.attr_span))
    }
}

pub(crate) struct ColdParser;

impl NoArgsAttributeParser for ColdParser {
    const PATH: &[Symbol] = &[sym::cold];
    const ON_DUPLICATE: OnDuplicate = OnDuplicate::Warn;
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowListWarnRest(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::ForeignFn),
        Allow(Target::Closure),
    ]);
    const STABILITY: AttributeStability = AttributeStability::Stable;
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Cold;
}

pub(crate) struct CoverageParser;

impl SingleAttributeParser for CoverageParser {
    const PATH: &[Symbol] = &[sym::coverage];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Closure),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Impl { of_trait: true }),
        Allow(Target::Impl { of_trait: false }),
        Allow(Target::Mod),
        Allow(Target::Crate),
    ]);
    const TEMPLATE: AttributeTemplate = template!(OneOf: &[sym::off, sym::on]);
    const STABILITY: AttributeStability = unstable!(coverage_attribute);

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

        let mut fail_incorrect_argument =
            |span| cx.adcx().expected_specific_argument(span, &[sym::on, sym::off]);

        let Some(arg) = arg.meta_item_no_args() else {
            fail_incorrect_argument(arg.span());
            return None;
        };

        let kind = match arg.path().word_sym() {
            Some(sym::off) => CoverageAttrKind::Off,
            Some(sym::on) => CoverageAttrKind::On,
            None | Some(_) => {
                fail_incorrect_argument(arg.span());
                return None;
            }
        };

        Some(AttributeKind::Coverage(kind))
    }
}

pub(crate) struct ExportNameParser;

impl SingleAttributeParser for ExportNameParser {
    const PATH: &[rustc_span::Symbol] = &[sym::export_name];
    const ON_DUPLICATE: OnDuplicate = OnDuplicate::WarnButFutureError;
    const SAFETY: AttributeSafety = AttributeSafety::Unsafe {
        note: "the linker's behavior with multiple libraries exporting duplicate symbol names is undefined and Rust cannot provide guarantees when you manually override them",
        unsafe_since: Some(Edition2024),
    };
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Static),
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Warn(Target::Field),
        Warn(Target::Arm),
        Warn(Target::MacroDef),
        Warn(Target::MacroCall),
    ]);
    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "name");
    const STABILITY: AttributeStability = AttributeStability::Stable;

    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)?;
        if name.as_str().contains('\0') {
            // `#[export_name = ...]` will be converted to a null-terminated string,
            // so it may not contain any null characters.
            cx.emit_err(NullOnExport { span: cx.attr_span });
            return None;
        }
        if name.is_empty() {
            // LLVM will make up a name if the empty string is given, but that name will be
            // inconsistent between compilation units, causing linker errors.
            cx.emit_err(EmptyExportName { span: cx.attr_span });
            return None;
        }
        Some(AttributeKind::ExportName { name, span: cx.attr_span })
    }
}

pub(crate) struct RustcObjcClassParser;

impl SingleAttributeParser for RustcObjcClassParser {
    const PATH: &[rustc_span::Symbol] = &[sym::rustc_objc_class];
    const ALLOWED_TARGETS: AllowedTargets<'_> =
        AllowedTargets::AllowList(&[Allow(Target::ForeignStatic)]);
    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "ClassName");
    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 Some(classname) = nv.value_as_str() else {
            // `#[rustc_objc_class = ...]` is expected to be used as an implementation detail
            // inside a standard library macro, but `cx.expected_string_literal` exposes too much.
            // Use a custom error message instead.
            cx.emit_err(ObjcClassExpectedStringLiteral { span: nv.value_span });
            return None;
        };
        if classname.as_str().contains('\0') {
            // `#[rustc_objc_class = ...]` will be converted to a null-terminated string,
            // so it may not contain any null characters.
            cx.emit_err(NullOnObjcClass { span: nv.value_span });
            return None;
        }
        Some(AttributeKind::RustcObjcClass { classname })
    }
}

pub(crate) struct RustcObjcSelectorParser;

impl SingleAttributeParser for RustcObjcSelectorParser {
    const PATH: &[rustc_span::Symbol] = &[sym::rustc_objc_selector];
    const ALLOWED_TARGETS: AllowedTargets<'_> =
        AllowedTargets::AllowList(&[Allow(Target::ForeignStatic)]);
    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "methodName");
    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 Some(methname) = nv.value_as_str() else {
            // `#[rustc_objc_selector = ...]` is expected to be used as an implementation detail
            // inside a standard library macro, but `cx.expected_string_literal` exposes too much.
            // Use a custom error message instead.
            cx.emit_err(ObjcSelectorExpectedStringLiteral { span: nv.value_span });
            return None;
        };
        if methname.as_str().contains('\0') {
            // `#[rustc_objc_selector = ...]` will be converted to a null-terminated string,
            // so it may not contain any null characters.
            cx.emit_err(NullOnObjcSelector { span: nv.value_span });
            return None;
        }
        Some(AttributeKind::RustcObjcSelector { methname })
    }
}

#[derive(Default)]
pub(crate) struct NakedParser {
    span: Option<Span>,
}

impl AttributeParser for NakedParser {
    const ATTRIBUTES: AcceptMapping<Self> =
        &[(&[sym::naked], template!(Word), AttributeStability::Stable, |this, cx, args| {
            let Some(()) = cx.expect_no_args(args) else {
                return;
            };

            if let Some(earlier) = this.span {
                let span = cx.attr_span;
                cx.warn_unused_duplicate(earlier, span);
            } else {
                this.span = Some(cx.attr_span);
            }
        })];
    const SAFETY: AttributeSafety = AttributeSafety::Unsafe {
        note: "the `#[naked]` attribute adds the safety obligation that the function's body must respect the function’s calling convention, uphold its signature, and either return or diverge (i.e., not fall through past the end of the assembly code).",
        unsafe_since: None,
    };
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Warn(Target::MacroCall),
    ]);

    fn finalize(self, cx: &FinalizeContext<'_, '_>) -> Option<AttributeKind> {
        // FIXME(jdonszelmann): upgrade this list to *parsed* attributes
        // once all of these have parsed forms. That'd make the check much nicer...
        //
        // many attributes don't make sense in combination with #[naked].
        // Notable attributes that are incompatible with `#[naked]` are:
        //
        // * `#[inline]`
        // * `#[track_caller]`
        // * `#[test]`, `#[ignore]`, `#[should_panic]`
        //
        // NOTE: when making changes to this list, check that `error_codes/E0736.md` remains
        // accurate.
        const ALLOW_LIST: &[rustc_span::Symbol] = &[
            // testing (allowed here so better errors can be generated in `rustc_builtin_macros::test`)
            sym::test,
            sym::ignore,
            sym::should_panic,
            sym::bench,
            // diagnostics
            sym::allow,
            sym::warn,
            sym::deny,
            sym::forbid,
            sym::deprecated,
            sym::must_use,
            // abi, linking and FFI
            sym::cold,
            sym::export_name,
            sym::link_section,
            sym::linkage,
            sym::no_mangle,
            sym::instruction_set,
            sym::repr,
            sym::rustc_std_internal_symbol,
            // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
            sym::rustc_align,
            sym::rustc_align_static,
            // obviously compatible with self
            sym::naked,
            // documentation
            sym::doc,
        ];

        let span = self.span?;

        let Some(tools) = cx.attr_tools else {
            unreachable!("tools required while parsing attributes");
        };

        // only if we found a naked attribute do we do the somewhat expensive check
        'outer: for other_attr in cx.all_attrs {
            for allowed_attr in ALLOW_LIST {
                if other_attr
                    .segments()
                    .next()
                    .is_some_and(|i| tools.iter().any(|tool| tool.name == i.name))
                {
                    // effectively skips the error message  being emitted below
                    // if it's a tool attribute
                    continue 'outer;
                }
                if other_attr.word_is(*allowed_attr) {
                    // effectively skips the error message  being emitted below
                    // if its an allowed attribute
                    continue 'outer;
                }

                if other_attr.word_is(sym::target_feature) {
                    if !cx.features().naked_functions_target_feature() {
                        feature_err(
                            cx.sess(),
                            sym::naked_functions_target_feature,
                            other_attr.span(),
                            "`#[target_feature(/* ... */)]` is currently unstable on `#[naked]` functions",
                        ).emit();
                    }

                    continue 'outer;
                }
            }

            cx.emit_err(NakedFunctionIncompatibleAttribute {
                span: other_attr.span(),
                naked_span: span,
                attr: other_attr.get_attribute_path().to_string(),
            });
        }

        Some(AttributeKind::Naked(span))
    }
}

pub(crate) struct TrackCallerParser;
impl NoArgsAttributeParser for TrackCallerParser {
    const PATH: &[Symbol] = &[sym::track_caller];
    const ON_DUPLICATE: OnDuplicate = OnDuplicate::Warn;
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Method(MethodKind::Trait { body: false })), // `#[track_caller]` is inherited from trait methods
        Allow(Target::ForeignFn),
        Allow(Target::Closure),
        Warn(Target::MacroDef),
        Warn(Target::Arm),
        Warn(Target::Field),
        Warn(Target::MacroCall),
    ]);
    const STABILITY: AttributeStability = AttributeStability::Stable;
    const CREATE: fn(Span) -> AttributeKind = AttributeKind::TrackCaller;

    fn finalize_check(cx: &FinalizeCheckContext<'_, '_>, attr_span: Span) {
        match cx.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(item) = find_attr!(cx.parsed_attrs, Lang(item) => item)
                    && item.is_weak()
                {
                    cx.emit_err(TrackCallerOnLangItem {
                        attr_span,
                        name: item.name(),
                        sig_span: cx.target_span,
                    });
                }
            }
            Target::Closure if !cx.features().closure_track_caller() => {
                feature_err(
                    cx.sess(),
                    sym::closure_track_caller,
                    attr_span,
                    "`#[track_caller]` on closures is currently unstable",
                )
                .emit();
            }
            _ => {}
        }
    }
}

pub(crate) struct NoMangleParser;
impl NoArgsAttributeParser for NoMangleParser {
    const PATH: &[Symbol] = &[sym::no_mangle];
    const ON_DUPLICATE: OnDuplicate = OnDuplicate::Warn;
    const SAFETY: AttributeSafety = AttributeSafety::Unsafe {
        note: "the linker's behavior with multiple libraries exporting duplicate symbol names is undefined and Rust cannot provide guarantees when you manually override them",
        unsafe_since: Some(Edition2024),
    };
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowListWarnRest(&[
        Allow(Target::Fn),
        Allow(Target::Static),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::TraitImpl)),
        AllowSilent(Target::Const), // Handled in the `InvalidNoMangleItems` pass
        Error(Target::Closure),
    ]);
    const STABILITY: AttributeStability = AttributeStability::Stable;
    const CREATE: fn(Span) -> AttributeKind = AttributeKind::NoMangle;
}

#[derive(Default)]
pub(crate) struct UsedParser {
    first_compiler: Option<Span>,
    first_linker: Option<Span>,
    first_default: Option<Span>,
}

// A custom `AttributeParser` is used rather than a Simple attribute parser because
// - Specifying two `#[used]` attributes is a warning (but will be an error in the future)
// - But specifying two conflicting attributes: `#[used(compiler)]` and `#[used(linker)]` is already an error today
// We can change this to a Simple parser once the warning becomes an error
impl AttributeParser for UsedParser {
    const ATTRIBUTES: AcceptMapping<Self> = &[(
        &[sym::used],
        template!(Word, List: &["compiler", "linker"]),
        AttributeStability::Stable,
        |group: &mut Self, cx, args| {
            let used_by = match args {
                ArgParser::NoArgs => UsedBy::Default,
                ArgParser::List(list) => {
                    let Some(l) = cx.expect_single(list) else {
                        return;
                    };

                    match l.meta_item_no_args().and_then(|i| i.path().word_sym()) {
                        Some(sym::compiler) => {
                            if !cx.features().used_with_arg() {
                                feature_err(
                                    cx.sess(),
                                    sym::used_with_arg,
                                    cx.attr_span,
                                    "`#[used(compiler)]` is currently unstable",
                                )
                                .emit();
                            }
                            UsedBy::Compiler
                        }
                        Some(sym::linker) => {
                            if !cx.features().used_with_arg() {
                                feature_err(
                                    cx.sess(),
                                    sym::used_with_arg,
                                    cx.attr_span,
                                    "`#[used(linker)]` is currently unstable",
                                )
                                .emit();
                            }
                            UsedBy::Linker
                        }
                        _ => {
                            cx.adcx().expected_specific_argument(
                                l.span(),
                                &[sym::compiler, sym::linker],
                            );
                            return;
                        }
                    }
                }
                ArgParser::NameValue(_) => return,
            };

            let attr_span = cx.attr_span;

            // `#[used]` is interpreted as `#[used(linker)]` (though depending on target OS the
            // circumstances are more complicated). While we're checking `used_by`, also report
            // these cross-`UsedBy` duplicates to warn.
            let target = match used_by {
                UsedBy::Compiler => &mut group.first_compiler,
                UsedBy::Linker => {
                    if let Some(prev) = group.first_default {
                        cx.warn_unused_duplicate(prev, attr_span);
                        return;
                    }
                    &mut group.first_linker
                }
                UsedBy::Default => {
                    if let Some(prev) = group.first_linker {
                        cx.warn_unused_duplicate(prev, attr_span);
                        return;
                    }
                    &mut group.first_default
                }
            };

            if let Some(prev) = *target {
                cx.warn_unused_duplicate(prev, attr_span);
            } else {
                *target = Some(attr_span);
            }
        },
    )];
    const ALLOWED_TARGETS: AllowedTargets<'_> =
        AllowedTargets::AllowList(&[Allow(Target::Static), Warn(Target::MacroCall)]);

    fn finalize(self, _cx: &FinalizeContext<'_, '_>) -> Option<AttributeKind> {
        // If a specific form of `used` is specified, it takes precedence over generic `#[used]`.
        // If both `linker` and `compiler` are specified, use `linker`.
        Some(match (self.first_compiler, self.first_linker, self.first_default) {
            (_, Some(_), _) => AttributeKind::Used { used_by: UsedBy::Linker },
            (Some(_), _, _) => AttributeKind::Used { used_by: UsedBy::Compiler },
            (_, _, Some(_)) => AttributeKind::Used { used_by: UsedBy::Default },
            (None, None, None) => return None,
        })
    }
}

fn parse_tf_attribute(
    cx: &mut AcceptContext<'_, '_>,
    args: &ArgParser,
) -> impl IntoIterator<Item = (Symbol, Span)> {
    let mut features = Vec::new();
    let Some(list) = cx.expect_list(args, cx.attr_span) else {
        return features;
    };
    if list.is_empty() {
        let attr_span = cx.attr_span;
        cx.adcx().warn_empty_attribute(attr_span);
        return features;
    }
    for item in list.mixed() {
        let Some((ident, value)) = cx.expect_name_value(item, item.span(), Some(sym::enable))
        else {
            return features;
        };

        // Validate name
        if ident.name != sym::enable {
            cx.adcx().expected_specific_argument(ident.span, &[sym::enable]);
            return features;
        }

        // Use value
        let Some(value_str) = cx.expect_string_literal(value) else {
            return features;
        };
        for feature in value_str.as_str().split(',') {
            features.push((Symbol::intern(feature), item.span()));
        }
    }
    features
}

pub(crate) struct TargetFeatureParser;

impl CombineAttributeParser for TargetFeatureParser {
    type Item = (Symbol, Span);
    const PATH: &[Symbol] = &[sym::target_feature];
    const CONVERT: ConvertFn<Self::Item> = |items, span| AttributeKind::TargetFeature {
        features: items,
        attr_span: span,
        was_forced: false,
    };
    const TEMPLATE: AttributeTemplate = template!(List: &["enable = \"feat1, feat2\""]);
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Warn(Target::Statement),
        Warn(Target::Field),
        Warn(Target::Arm),
        Warn(Target::MacroDef),
        Warn(Target::MacroCall),
    ]);
    const STABILITY: AttributeStability = AttributeStability::Stable;

    fn extend(
        cx: &mut AcceptContext<'_, '_>,
        args: &ArgParser,
    ) -> impl IntoIterator<Item = Self::Item> {
        parse_tf_attribute(cx, args)
    }

    fn finalize_check(cx: &FinalizeCheckContext<'_, '_>, attr_span: Span) {
        // `#[target_feature]` is incompatible with lang item functions,
        // except on WASM where calling target-feature functions is safe (see #84988).
        if !cx.sess().target.is_like_wasm && !cx.sess().opts.actually_rustdoc {
            // `#[panic_handler]` is checked first so it takes priority in the diagnostic.
            let lang_kind = cx
                .all_attrs
                .iter()
                .find_map(|a| [sym::panic_handler, sym::lang].into_iter().find(|&s| a.word_is(s)));
            if let Some(kind) = lang_kind {
                cx.emit_err(TargetFeatureOnLangItem { attr_span, kind, item_span: cx.target_span });
            }
        }
    }
}

pub(crate) struct ForceTargetFeatureParser;

impl CombineAttributeParser for ForceTargetFeatureParser {
    type Item = (Symbol, Span);
    const PATH: &[Symbol] = &[sym::force_target_feature];
    const SAFETY: AttributeSafety = AttributeSafety::Unsafe {
        note: "a function with the signature of the function the attribute is applied to must only be callable if the force-enabled features are guaranteed to be present",
        unsafe_since: None,
    };
    const CONVERT: ConvertFn<Self::Item> = |items, span| AttributeKind::TargetFeature {
        features: items,
        attr_span: span,
        was_forced: true,
    };
    const TEMPLATE: AttributeTemplate = template!(List: &["enable = \"feat1, feat2\""]);
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
    ]);
    const STABILITY: AttributeStability = unstable!(effective_target_features);

    fn extend(
        cx: &mut AcceptContext<'_, '_>,
        args: &ArgParser,
    ) -> impl IntoIterator<Item = Self::Item> {
        parse_tf_attribute(cx, args)
    }
}

pub(crate) struct InstrumentFnParser;

impl SingleAttributeParser for InstrumentFnParser {
    const PATH: &[Symbol] = &[sym::instrument_fn];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
    ]);
    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "on|off");
    const STABILITY: AttributeStability = unstable!(instrument_fn);

    fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind> {
        match args {
            ArgParser::NameValue(nv) => match nv.value_as_str() {
                Some(sym::on) => Some(AttributeKind::InstrumentFn(InstrumentFnAttr::On)),
                Some(sym::off) => Some(AttributeKind::InstrumentFn(InstrumentFnAttr::Off)),
                _ => {
                    cx.adcx()
                        .expected_specific_argument_strings(nv.value_span, &[sym::on, sym::off]);
                    None
                }
            },
            ArgParser::List(l) => {
                cx.adcx().expected_single_argument(l.span, l.len());
                None
            }
            ArgParser::NoArgs => {
                let span = cx.attr_span;
                cx.adcx().expected_specific_argument_strings(span, &[sym::on, sym::off]);
                None
            }
        }
    }
}

pub(crate) struct SanitizeParser;

impl SingleAttributeParser for SanitizeParser {
    const PATH: &[Symbol] = &[sym::sanitize];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
        Allow(Target::Fn),
        Allow(Target::Closure),
        Allow(Target::Method(MethodKind::Inherent)),
        Allow(Target::Method(MethodKind::Trait { body: true })),
        Allow(Target::Method(MethodKind::TraitImpl)),
        Allow(Target::Impl { of_trait: false }),
        Allow(Target::Impl { of_trait: true }),
        Allow(Target::Mod),
        Allow(Target::Crate),
        Allow(Target::Static),
    ]);
    const TEMPLATE: AttributeTemplate = template!(List: &[
        r#"address = "on|off""#,
        r#"kernel_address = "on|off""#,
        r#"cfi = "on|off""#,
        r#"hwaddress = "on|off""#,
        r#"kernel_hwaddress = "on|off""#,
        r#"kcfi = "on|off""#,
        r#"memory = "on|off""#,
        r#"memtag = "on|off""#,
        r#"safestack = "on|off""#,
        r#"shadow_call_stack = "on|off""#,
        r#"thread = "on|off""#,
        r#"realtime = "nonblocking|blocking|caller""#,
    ]);
    const STABILITY: AttributeStability = unstable!(sanitize);

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

        let mut on_set = SanitizerSet::empty();
        let mut off_set = SanitizerSet::empty();
        let mut rtsan = None;

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

            let mut apply = |s: SanitizerSet| {
                let is_on = match value.value_as_str() {
                    Some(sym::on) => true,
                    Some(sym::off) => false,
                    _ => {
                        cx.adcx().expected_specific_argument_strings(
                            value.value_span,
                            &[sym::on, sym::off],
                        );
                        return;
                    }
                };

                if is_on {
                    on_set |= s;
                } else {
                    off_set |= s;
                }
            };

            match ident.name {
                sym::address | sym::kernel_address => {
                    apply(SanitizerSet::ADDRESS | SanitizerSet::KERNELADDRESS)
                }
                sym::cfi => apply(SanitizerSet::CFI),
                sym::kcfi => apply(SanitizerSet::KCFI),
                sym::memory => apply(SanitizerSet::MEMORY),
                sym::memtag => apply(SanitizerSet::MEMTAG),
                sym::safestack => apply(SanitizerSet::SAFESTACK),
                sym::shadow_call_stack => apply(SanitizerSet::SHADOWCALLSTACK),
                sym::thread => apply(SanitizerSet::THREAD),
                sym::hwaddress | sym::kernel_hwaddress => {
                    apply(SanitizerSet::HWADDRESS | SanitizerSet::KERNELHWADDRESS)
                }
                sym::realtime => match value.value_as_str() {
                    Some(sym::nonblocking) => rtsan = Some(RtsanSetting::Nonblocking),
                    Some(sym::blocking) => rtsan = Some(RtsanSetting::Blocking),
                    Some(sym::caller) => rtsan = Some(RtsanSetting::Caller),
                    _ => {
                        cx.adcx().expected_specific_argument_strings(
                            value.value_span,
                            &[sym::nonblocking, sym::blocking, sym::caller],
                        );
                    }
                },
                _ => {
                    cx.adcx().expected_specific_argument_strings(
                        ident.span,
                        &[
                            sym::address,
                            sym::kernel_address,
                            sym::cfi,
                            sym::kcfi,
                            sym::memory,
                            sym::memtag,
                            sym::safestack,
                            sym::shadow_call_stack,
                            sym::thread,
                            sym::hwaddress,
                            sym::kernel_hwaddress,
                            sym::realtime,
                        ],
                    );
                }
            }
        }

        // The sanitizer attribute is only allowed on statics, if only address bits are set
        let all_set_except_address =
            (on_set | off_set) & !(SanitizerSet::ADDRESS | SanitizerSet::KERNELADDRESS);
        if cx.target == Target::Static
            && let Some(set) = all_set_except_address.iter().next()
        {
            cx.emit_err(SanitizeInvalidStatic {
                span: cx.attr_span,
                field: set.as_str().expect("Since this `SanitizerSet` is returned from an iterator, exactly one field is set")
            });
        }

        Some(AttributeKind::Sanitize { on_set, off_set, rtsan, span: cx.attr_span })
    }
}

pub(crate) struct ThreadLocalParser;

impl NoArgsAttributeParser for ThreadLocalParser {
    const PATH: &[Symbol] = &[sym::thread_local];
    const ALLOWED_TARGETS: AllowedTargets<'_> =
        AllowedTargets::AllowList(&[Allow(Target::Static), Allow(Target::ForeignStatic)]);
    const STABILITY: AttributeStability = unstable!(thread_local);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::ThreadLocal;
}

pub(crate) struct RustcPassIndirectlyInNonRusticAbisParser;

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

pub(crate) struct RustcEiiForeignItemParser;

impl NoArgsAttributeParser for RustcEiiForeignItemParser {
    const PATH: &[Symbol] = &[sym::rustc_eii_foreign_item];
    const ALLOWED_TARGETS: AllowedTargets<'_> =
        AllowedTargets::AllowList(&[Allow(Target::ForeignFn), Allow(Target::ForeignStatic)]);
    const STABILITY: AttributeStability = unstable!(eii_internals);
    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcEiiForeignItem;
}

pub(crate) struct PatchableFunctionEntryParser;

impl SingleAttributeParser for PatchableFunctionEntryParser {
    const PATH: &[Symbol] = &[sym::patchable_function_entry];
    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
    const TEMPLATE: AttributeTemplate =
        template!(List: &["prefix_nops = m, entry_nops = n, section = \"section\""]);
    const STABILITY: AttributeStability = unstable!(patchable_function_entry);

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

        let mut prefix = None;
        let mut entry = None;
        let mut section = None;

        if meta_item_list.len() == 0 {
            cx.adcx().expected_at_least_one_argument(meta_item_list.span);
            return None;
        }

        for item in meta_item_list.mixed() {
            let (ident, value) = cx.expect_name_value(item, item.span(), None)?;

            let attrib_to_write = match ident.name {
                sym::prefix_nops => {
                    // Duplicate prefixes are not allowed
                    if prefix.is_some() {
                        cx.adcx().duplicate_key(ident.span, sym::prefix_nops);
                        return None;
                    }
                    &mut prefix
                }
                sym::entry_nops => {
                    // Duplicate entries are not allowed
                    if entry.is_some() {
                        cx.adcx().duplicate_key(ident.span, sym::entry_nops);
                        return None;
                    }
                    &mut entry
                }
                sym::section => {
                    // Duplicate entries are not allowed
                    if section.is_some() {
                        cx.adcx().duplicate_key(ident.span, sym::section);
                        return None;
                    }
                    // Only a string type value is allowed.
                    let Some(value_str) = value.value_as_str() else {
                        cx.adcx().expect_string_literal(value);
                        return None;
                    };
                    // The section name does not allow null characters.
                    if value_str.as_str().contains('\0') {
                        cx.emit_err(NullOnSection { span: value.value_span });
                    }
                    // The section name is not allowed to be empty, LLVM does
                    // not allow them.
                    if value_str.is_empty() {
                        cx.emit_err(EmptySection { span: value.value_span });
                    }
                    section = Some(value_str);
                    // Integer parsing is not needed, process next item.
                    continue;
                }
                _ => {
                    cx.adcx().expected_specific_argument(
                        ident.span,
                        &[sym::prefix_nops, sym::entry_nops],
                    );
                    return None;
                }
            };

            let rustc_ast::LitKind::Int(val, _) = value.value_as_lit().kind else {
                cx.adcx().expected_integer_literal(value.value_span);
                return None;
            };

            let Ok(val) = val.get().try_into() else {
                cx.adcx().expected_integer_literal_in_range(
                    value.value_span,
                    u8::MIN as isize,
                    u8::MAX as isize,
                );
                return None;
            };

            *attrib_to_write = Some(val);
        }

        Some(AttributeKind::PatchableFunctionEntry { prefix, entry, section })
    }
}