path: root/compiler/rustc_hir/src/attrs/data_structures.rs

use std::borrow::Cow;
use std::path::PathBuf;

pub use ReprAttr::*;
use rustc_abi::Align;
use rustc_ast::token::CommentKind;
use rustc_ast::{AttrStyle, ast};
use rustc_error_messages::{DiagArgValue, IntoDiagArg};
use rustc_macros::{Decodable, Encodable, HashStable_Generic, PrintAttribute};
use rustc_span::def_id::DefId;
use rustc_span::hygiene::Transparency;
use rustc_span::{Ident, Span, Symbol};
pub use rustc_target::spec::SanitizerSet;
use thin_vec::ThinVec;

use crate::attrs::pretty_printing::PrintAttribute;
use crate::limit::Limit;
use crate::{DefaultBodyStability, PartialConstStability, RustcVersion, Stability};

#[derive(Copy, Clone, PartialEq, Encodable, Decodable, Debug, HashStable_Generic, PrintAttribute)]
pub enum InlineAttr {
    None,
    Hint,
    Always,
    Never,
    /// `#[rustc_force_inline]` forces inlining to happen in the MIR inliner - it reports an error
    /// if the inlining cannot happen. It is limited to only free functions so that the calls
    /// can always be resolved.
    Force {
        attr_span: Span,
        reason: Option<Symbol>,
    },
}

impl InlineAttr {
    pub fn always(&self) -> bool {
        match self {
            InlineAttr::Always | InlineAttr::Force { .. } => true,
            InlineAttr::None | InlineAttr::Hint | InlineAttr::Never => false,
        }
    }
}

#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq, HashStable_Generic)]
pub enum InstructionSetAttr {
    ArmA32,
    ArmT32,
}

#[derive(Copy, Clone, Debug, PartialEq, Eq, Default, PrintAttribute)]
#[derive(Encodable, Decodable, HashStable_Generic)]
pub enum OptimizeAttr {
    /// No `#[optimize(..)]` attribute
    #[default]
    Default,
    /// `#[optimize(none)]`
    DoNotOptimize,
    /// `#[optimize(speed)]`
    Speed,
    /// `#[optimize(size)]`
    Size,
}

impl OptimizeAttr {
    pub fn do_not_optimize(&self) -> bool {
        matches!(self, Self::DoNotOptimize)
    }
}

#[derive(PartialEq, Debug, Encodable, Decodable, Copy, Clone, HashStable_Generic, PrintAttribute)]
pub enum ReprAttr {
    ReprInt(IntType),
    ReprRust,
    ReprC,
    ReprPacked(Align),
    ReprSimd,
    ReprTransparent,
    ReprAlign(Align),
}

pub enum TransparencyError {
    UnknownTransparency(Symbol, Span),
    MultipleTransparencyAttrs(Span, Span),
}

#[derive(Eq, PartialEq, Debug, Copy, Clone)]
#[derive(Encodable, Decodable, HashStable_Generic, PrintAttribute)]
pub enum IntType {
    SignedInt(ast::IntTy),
    UnsignedInt(ast::UintTy),
}

#[derive(Copy, Debug, Encodable, Decodable, Clone, HashStable_Generic, PrintAttribute)]
pub struct Deprecation {
    pub since: DeprecatedSince,
    /// The note to issue a reason.
    pub note: Option<Symbol>,
    /// A text snippet used to completely replace any use of the deprecated item in an expression.
    ///
    /// This is currently unstable.
    pub suggestion: Option<Symbol>,
}

/// Release in which an API is deprecated.
#[derive(Copy, Debug, Encodable, Decodable, Clone, HashStable_Generic, PrintAttribute)]
pub enum DeprecatedSince {
    RustcVersion(RustcVersion),
    /// Deprecated in the future ("to be determined").
    Future,
    /// `feature(staged_api)` is off. Deprecation versions outside the standard
    /// library are allowed to be arbitrary strings, for better or worse.
    NonStandard(Symbol),
    /// Deprecation version is unspecified but optional.
    Unspecified,
    /// Failed to parse a deprecation version, or the deprecation version is
    /// unspecified and required. An error has already been emitted.
    Err,
}

/// Successfully-parsed value of a `#[coverage(..)]` attribute.
#[derive(Copy, Debug, Eq, PartialEq, Encodable, Decodable, Clone)]
#[derive(HashStable_Generic, PrintAttribute)]
pub enum CoverageAttrKind {
    On,
    Off,
}

impl Deprecation {
    /// Whether an item marked with #[deprecated(since = "X")] is currently
    /// deprecated (i.e., whether X is not greater than the current rustc
    /// version).
    pub fn is_in_effect(&self) -> bool {
        match self.since {
            DeprecatedSince::RustcVersion(since) => since <= RustcVersion::CURRENT,
            DeprecatedSince::Future => false,
            // The `since` field doesn't have semantic purpose without `#![staged_api]`.
            DeprecatedSince::NonStandard(_) => true,
            // Assume deprecation is in effect if "since" field is absent or invalid.
            DeprecatedSince::Unspecified | DeprecatedSince::Err => true,
        }
    }

    pub fn is_since_rustc_version(&self) -> bool {
        matches!(self.since, DeprecatedSince::RustcVersion(_))
    }
}

/// There are three valid forms of the attribute:
/// `#[used]`, which is equivalent to `#[used(linker)]` on targets that support it, but `#[used(compiler)]` if not.
/// `#[used(compiler)]`
/// `#[used(linker)]`
#[derive(Encodable, Decodable, Copy, Clone, Debug, PartialEq, Eq, Hash)]
#[derive(HashStable_Generic, PrintAttribute)]
pub enum UsedBy {
    Default,
    Compiler,
    Linker,
}

#[derive(Encodable, Decodable, Clone, Debug, PartialEq, Eq, Hash)]
#[derive(HashStable_Generic, PrintAttribute)]
pub enum MacroUseArgs {
    UseAll,
    UseSpecific(ThinVec<Ident>),
}

impl Default for MacroUseArgs {
    fn default() -> Self {
        Self::UseSpecific(ThinVec::new())
    }
}

#[derive(Debug, Clone, Encodable, Decodable, HashStable_Generic)]
pub struct StrippedCfgItem<ModId = DefId> {
    pub parent_module: ModId,
    pub ident: Ident,
    pub cfg: (CfgEntry, Span),
}

impl<ModId> StrippedCfgItem<ModId> {
    pub fn map_mod_id<New>(self, f: impl FnOnce(ModId) -> New) -> StrippedCfgItem<New> {
        StrippedCfgItem { parent_module: f(self.parent_module), ident: self.ident, cfg: self.cfg }
    }
}

#[derive(Encodable, Decodable, Clone, Debug, PartialEq, Eq, Hash)]
#[derive(HashStable_Generic, PrintAttribute)]
pub enum CfgEntry {
    All(ThinVec<CfgEntry>, Span),
    Any(ThinVec<CfgEntry>, Span),
    Not(Box<CfgEntry>, Span),
    Bool(bool, Span),
    NameValue { name: Symbol, name_span: Span, value: Option<(Symbol, Span)>, span: Span },
    Version(Option<RustcVersion>, Span),
}

/// Possible values for the `#[linkage]` attribute, allowing to specify the
/// linkage type for a `MonoItem`.
///
/// See <https://llvm.org/docs/LangRef.html#linkage-types> for more details about these variants.
#[derive(Encodable, Decodable, Clone, Copy, Debug, PartialEq, Eq, Hash)]
#[derive(HashStable_Generic, PrintAttribute)]
pub enum Linkage {
    AvailableExternally,
    Common,
    ExternalWeak,
    External,
    Internal,
    LinkOnceAny,
    LinkOnceODR,
    WeakAny,
    WeakODR,
}

#[derive(Clone, Copy, Decodable, Debug, Encodable, PartialEq)]
#[derive(HashStable_Generic, PrintAttribute)]
pub enum MirDialect {
    Analysis,
    Built,
    Runtime,
}

impl IntoDiagArg for MirDialect {
    fn into_diag_arg(self, _path: &mut Option<PathBuf>) -> DiagArgValue {
        let arg = match self {
            MirDialect::Analysis => "analysis",
            MirDialect::Built => "built",
            MirDialect::Runtime => "runtime",
        };
        DiagArgValue::Str(Cow::Borrowed(arg))
    }
}

#[derive(Clone, Copy, Decodable, Debug, Encodable, PartialEq)]
#[derive(HashStable_Generic, PrintAttribute)]
pub enum MirPhase {
    Initial,
    PostCleanup,
    Optimized,
}

impl IntoDiagArg for MirPhase {
    fn into_diag_arg(self, _path: &mut Option<PathBuf>) -> DiagArgValue {
        let arg = match self {
            MirPhase::Initial => "initial",
            MirPhase::PostCleanup => "post-cleanup",
            MirPhase::Optimized => "optimized",
        };
        DiagArgValue::Str(Cow::Borrowed(arg))
    }
}

/// Different ways that the PE Format can decorate a symbol name.
/// From <https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#import-name-type>
#[derive(
    Copy,
    Clone,
    Debug,
    Encodable,
    Decodable,
    HashStable_Generic,
    PartialEq,
    Eq,
    PrintAttribute
)]
pub enum PeImportNameType {
    /// IMPORT_ORDINAL
    /// Uses the ordinal (i.e., a number) rather than the name.
    Ordinal(u16),
    /// Same as IMPORT_NAME
    /// Name is decorated with all prefixes and suffixes.
    Decorated,
    /// Same as IMPORT_NAME_NOPREFIX
    /// Prefix (e.g., the leading `_` or `@`) is skipped, but suffix is kept.
    NoPrefix,
    /// Same as IMPORT_NAME_UNDECORATE
    /// Prefix (e.g., the leading `_` or `@`) and suffix (the first `@` and all
    /// trailing characters) are skipped.
    Undecorated,
}

#[derive(
    Copy,
    Clone,
    Debug,
    PartialEq,
    Eq,
    PartialOrd,
    Ord,
    Hash,
    Encodable,
    Decodable,
    PrintAttribute
)]
#[derive(HashStable_Generic)]
pub enum NativeLibKind {
    /// Static library (e.g. `libfoo.a` on Linux or `foo.lib` on Windows/MSVC)
    Static {
        /// Whether to bundle objects from static library into produced rlib
        bundle: Option<bool>,
        /// Whether to link static library without throwing any object files away
        whole_archive: Option<bool>,
    },
    /// Dynamic library (e.g. `libfoo.so` on Linux)
    /// or an import library corresponding to a dynamic library (e.g. `foo.lib` on Windows/MSVC).
    Dylib {
        /// Whether the dynamic library will be linked only if it satisfies some undefined symbols
        as_needed: Option<bool>,
    },
    /// Dynamic library (e.g. `foo.dll` on Windows) without a corresponding import library.
    /// On Linux, it refers to a generated shared library stub.
    RawDylib,
    /// A macOS-specific kind of dynamic libraries.
    Framework {
        /// Whether the framework will be linked only if it satisfies some undefined symbols
        as_needed: Option<bool>,
    },
    /// Argument which is passed to linker, relative order with libraries and other arguments
    /// is preserved
    LinkArg,

    /// Module imported from WebAssembly
    WasmImportModule,

    /// The library kind wasn't specified, `Dylib` is currently used as a default.
    Unspecified,
}

impl NativeLibKind {
    pub fn has_modifiers(&self) -> bool {
        match self {
            NativeLibKind::Static { bundle, whole_archive } => {
                bundle.is_some() || whole_archive.is_some()
            }
            NativeLibKind::Dylib { as_needed } | NativeLibKind::Framework { as_needed } => {
                as_needed.is_some()
            }
            NativeLibKind::RawDylib
            | NativeLibKind::Unspecified
            | NativeLibKind::LinkArg
            | NativeLibKind::WasmImportModule => false,
        }
    }

    pub fn is_statically_included(&self) -> bool {
        matches!(self, NativeLibKind::Static { .. })
    }

    pub fn is_dllimport(&self) -> bool {
        matches!(
            self,
            NativeLibKind::Dylib { .. } | NativeLibKind::RawDylib | NativeLibKind::Unspecified
        )
    }
}

#[derive(Debug, Encodable, Decodable, Clone, HashStable_Generic, PrintAttribute)]
pub struct LinkEntry {
    pub span: Span,
    pub kind: NativeLibKind,
    pub name: Symbol,
    pub cfg: Option<CfgEntry>,
    pub verbatim: Option<bool>,
    pub import_name_type: Option<(PeImportNameType, Span)>,
}

#[derive(HashStable_Generic, PrintAttribute)]
#[derive(Copy, PartialEq, PartialOrd, Clone, Ord, Eq, Hash, Debug, Encodable, Decodable)]
pub enum DebuggerVisualizerType {
    Natvis,
    GdbPrettyPrinter,
}

#[derive(Debug, Encodable, Decodable, Clone, HashStable_Generic, PrintAttribute)]
pub struct DebugVisualizer {
    pub span: Span,
    pub visualizer_type: DebuggerVisualizerType,
    pub path: Symbol,
}

/// Represents parsed *built-in* inert attributes.
///
/// ## Overview
/// These attributes are markers that guide the compilation process and are never expanded into other code.
/// They persist throughout the compilation phases, from AST to HIR and beyond.
///
/// ## Attribute Processing
/// While attributes are initially parsed by [`rustc_parse`] into [`ast::Attribute`], they still contain raw token streams
/// because different attributes have different internal structures. This enum represents the final,
/// fully parsed form of these attributes, where each variant contains all the information and
/// structure relevant for the specific attribute.
///
/// Some attributes can be applied multiple times to the same item, and they are "collapsed" into a single
/// semantic attribute. For example:
/// ```rust
/// #[repr(C)]
/// #[repr(packed)]
/// struct S { }
/// ```
/// This is equivalent to `#[repr(C, packed)]` and results in a single [`AttributeKind::Repr`] containing
/// both `C` and `packed` annotations. This collapsing happens during parsing and is reflected in the
/// data structures defined in this enum.
///
/// ## Usage
/// These parsed attributes are used throughout the compiler to:
/// - Control code generation (e.g., `#[repr]`)
/// - Mark API stability (`#[stable]`, `#[unstable]`)
/// - Provide documentation (`#[doc]`)
/// - Guide compiler behavior (e.g., `#[allow_internal_unstable]`)
///
/// ## Note on Attribute Organization
/// Some attributes like `InlineAttr`, `OptimizeAttr`, and `InstructionSetAttr` are defined separately
/// from this enum because they are used in specific compiler phases (like code generation) and don't
/// need to persist throughout the entire compilation process. They are typically processed and
/// converted into their final form earlier in the compilation pipeline.
///
/// For example:
/// - `InlineAttr` is used during code generation to control function inlining
/// - `OptimizeAttr` is used to control optimization levels
/// - `InstructionSetAttr` is used for target-specific code generation
///
/// These attributes are handled by their respective compiler passes in the [`rustc_codegen_ssa`] crate
/// and don't need to be preserved in the same way as the attributes in this enum.
///
/// For more details on attribute parsing, see the [`rustc_attr_parsing`] crate.
///
/// [`rustc_parse`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/index.html
/// [`rustc_codegen_ssa`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/index.html
/// [`rustc_attr_parsing`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_attr_parsing/index.html
#[derive(Clone, Debug, HashStable_Generic, Encodable, Decodable, PrintAttribute)]
pub enum AttributeKind {
    // tidy-alphabetical-start
    /// Represents `#[align(N)]`.
    // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
    Align { align: Align, span: Span },

    /// Represents `#[rustc_allow_const_fn_unstable]`.
    AllowConstFnUnstable(ThinVec<Symbol>, Span),

    /// Represents `#[rustc_allow_incoherent_impl]`.
    AllowIncoherentImpl(Span),

    /// Represents `#[allow_internal_unsafe]`.
    AllowInternalUnsafe(Span),

    /// Represents `#[allow_internal_unstable]`.
    AllowInternalUnstable(ThinVec<(Symbol, Span)>, Span),

    /// Represents `#[rustc_as_ptr]` (used by the `dangling_pointers_from_temporaries` lint).
    AsPtr(Span),

    /// Represents `#[automatically_derived]`
    AutomaticallyDerived(Span),

    /// Represents `#[rustc_default_body_unstable]`.
    BodyStability {
        stability: DefaultBodyStability,
        /// Span of the `#[rustc_default_body_unstable(...)]` attribute
        span: Span,
    },

    /// Represents `#[rustc_coinductive]`.
    Coinductive(Span),

    /// Represents `#[cold]`.
    Cold(Span),

    /// Represents `#[rustc_confusables]`.
    Confusables {
        symbols: ThinVec<Symbol>,
        // FIXME(jdonszelmann): remove when target validation code is moved
        first_span: Span,
    },

    /// Represents `#[const_continue]`.
    ConstContinue(Span),

    /// Represents `#[rustc_const_stable]` and `#[rustc_const_unstable]`.
    ConstStability {
        stability: PartialConstStability,
        /// Span of the `#[rustc_const_stable(...)]` or `#[rustc_const_unstable(...)]` attribute
        span: Span,
    },

    /// Represents `#[rustc_const_stable_indirect]`.
    ConstStabilityIndirect,

    /// Represents `#[const_trait]`.
    ConstTrait(Span),

    /// Represents `#[coroutine]`.
    Coroutine(Span),

    /// Represents `#[coverage(..)]`.
    Coverage(Span, CoverageAttrKind),

    /// Represents `#[crate_name = ...]`
    CrateName { name: Symbol, name_span: Span, attr_span: Span, style: AttrStyle },

    /// Represents `#[custom_mir]`.
    CustomMir(Option<(MirDialect, Span)>, Option<(MirPhase, Span)>, Span),

    /// Represents `#[debugger_visualizer]`.
    DebuggerVisualizer(ThinVec<DebugVisualizer>),

    /// Represents `#[rustc_deny_explicit_impl]`.
    DenyExplicitImpl(Span),

    /// Represents [`#[deprecated]`](https://doc.rust-lang.org/stable/reference/attributes/diagnostics.html#the-deprecated-attribute).
    Deprecation { deprecation: Deprecation, span: Span },

    /// Represents `#[rustc_do_not_implement_via_object]`.
    DoNotImplementViaObject(Span),

    /// Represents [`#[doc]`](https://doc.rust-lang.org/stable/rustdoc/write-documentation/the-doc-attribute.html).
    DocComment { style: AttrStyle, kind: CommentKind, span: Span, comment: Symbol },

    /// Represents `#[rustc_dummy]`.
    Dummy,

    /// Represents [`#[export_name]`](https://doc.rust-lang.org/reference/abi.html#the-export_name-attribute).
    ExportName {
        /// The name to export this item with.
        /// It may not contain \0 bytes as it will be converted to a null-terminated string.
        name: Symbol,
        span: Span,
    },

    /// Represents `#[export_stable]`.
    ExportStable,

    /// Represents `#[ffi_const]`.
    FfiConst(Span),

    /// Represents `#[ffi_pure]`.
    FfiPure(Span),

    /// Represents `#[fundamental]`.
    Fundamental,

    /// Represents `#[ignore]`
    Ignore {
        span: Span,
        /// ignore can optionally have a reason: `#[ignore = "reason this is ignored"]`
        reason: Option<Symbol>,
    },

    /// Represents `#[inline]` and `#[rustc_force_inline]`.
    Inline(InlineAttr, Span),

    /// Represents `#[link]`.
    Link(ThinVec<LinkEntry>, Span),

    /// Represents `#[link_name]`.
    LinkName { name: Symbol, span: Span },

    /// Represents `#[link_ordinal]`.
    LinkOrdinal { ordinal: u16, span: Span },

    /// Represents [`#[link_section]`](https://doc.rust-lang.org/reference/abi.html#the-link_section-attribute)
    LinkSection { name: Symbol, span: Span },

    /// Represents `#[linkage]`.
    Linkage(Linkage, Span),

    /// Represents `#[loop_match]`.
    LoopMatch(Span),

    /// Represents `#[macro_escape]`.
    MacroEscape(Span),

    /// Represents [`#[macro_export]`](https://doc.rust-lang.org/reference/macros-by-example.html#r-macro.decl.scope.path).
    MacroExport { span: Span, local_inner_macros: bool },

    /// Represents `#[rustc_macro_transparency]`.
    MacroTransparency(Transparency),

    /// Represents `#[macro_use]`.
    MacroUse { span: Span, arguments: MacroUseArgs },

    /// Represents `#[marker]`.
    Marker(Span),

    /// Represents [`#[may_dangle]`](https://std-dev-guide.rust-lang.org/tricky/may-dangle.html).
    MayDangle(Span),

    /// Represents `#[move_size_limit]`
    MoveSizeLimit { attr_span: Span, limit_span: Span, limit: Limit },

    /// Represents `#[must_use]`.
    MustUse {
        span: Span,
        /// must_use can optionally have a reason: `#[must_use = "reason this must be used"]`
        reason: Option<Symbol>,
    },

    /// Represents `#[naked]`
    Naked(Span),

    /// Represents `#[no_core]`
    NoCore(Span),

    /// Represents `#[no_implicit_prelude]`
    NoImplicitPrelude(Span),

    /// Represents `#[no_mangle]`
    NoMangle(Span),

    /// Represents `#[no_std]`
    NoStd(Span),

    /// Represents `#[non_exhaustive]`
    NonExhaustive(Span),

    /// Represents `#[rustc_objc_class]`
    ObjcClass { classname: Symbol, span: Span },

    /// Represents `#[rustc_objc_selector]`
    ObjcSelector { methname: Symbol, span: Span },

    /// Represents `#[optimize(size|speed)]`
    Optimize(OptimizeAttr, Span),

    /// Represents `#[rustc_paren_sugar]`.
    ParenSugar(Span),

    /// Represents `#[rustc_pass_by_value]` (used by the `rustc_pass_by_value` lint).
    PassByValue(Span),

    /// Represents `#[path]`
    Path(Symbol, Span),

    /// Represents `#[pattern_complexity_limit]`
    PatternComplexityLimit { attr_span: Span, limit_span: Span, limit: Limit },

    /// Represents `#[pointee]`
    Pointee(Span),

    /// Represents `#[proc_macro]`
    ProcMacro(Span),

    /// Represents `#[proc_macro_attribute]`
    ProcMacroAttribute(Span),

    /// Represents `#[proc_macro_derive]`
    ProcMacroDerive { trait_name: Symbol, helper_attrs: ThinVec<Symbol>, span: Span },

    /// Represents `#[rustc_pub_transparent]` (used by the `repr_transparent_external_private_fields` lint).
    PubTransparent(Span),

    /// Represents [`#[recursion_limit]`](https://doc.rust-lang.org/reference/attributes/limits.html#the-recursion_limit-attribute)
    RecursionLimit { attr_span: Span, limit_span: Span, limit: Limit },

    /// Represents [`#[repr]`](https://doc.rust-lang.org/stable/reference/type-layout.html#representations).
    Repr { reprs: ThinVec<(ReprAttr, Span)>, first_span: Span },

    /// Represents `#[rustc_builtin_macro]`.
    RustcBuiltinMacro { builtin_name: Option<Symbol>, helper_attrs: ThinVec<Symbol>, span: Span },

    /// Represents `#[rustc_coherence_is_core]`
    RustcCoherenceIsCore(Span),

    /// Represents `#[rustc_layout_scalar_valid_range_end]`.
    RustcLayoutScalarValidRangeEnd(Box<u128>, Span),

    /// Represents `#[rustc_layout_scalar_valid_range_start]`.
    RustcLayoutScalarValidRangeStart(Box<u128>, Span),

    /// Represents `#[rustc_object_lifetime_default]`.
    RustcObjectLifetimeDefault,

    /// Represents `#[rustc_simd_monomorphize_lane_limit = "N"]`.
    RustcSimdMonomorphizeLaneLimit(Limit),

    /// Represents `#[sanitize]`
    ///
    /// the on set and off set are distjoint since there's a third option: unset.
    /// a node may not set the sanitizer setting in which case it inherits from parents.
    Sanitize { on_set: SanitizerSet, off_set: SanitizerSet, span: Span },

    /// Represents `#[should_panic]`
    ShouldPanic { reason: Option<Symbol>, span: Span },

    /// Represents `#[rustc_skip_during_method_dispatch]`.
    SkipDuringMethodDispatch { array: bool, boxed_slice: bool, span: Span },

    /// Represents `#[rustc_specialization_trait]`.
    SpecializationTrait(Span),

    /// Represents `#[stable]`, `#[unstable]` and `#[rustc_allowed_through_unstable_modules]`.
    Stability {
        stability: Stability,
        /// Span of the attribute.
        span: Span,
    },

    /// Represents `#[rustc_std_internal_symbol]`.
    StdInternalSymbol(Span),

    /// Represents `#[target_feature(enable = "...")]` and
    /// `#[unsafe(force_target_feature(enable = "...")]`.
    TargetFeature { features: ThinVec<(Symbol, Span)>, attr_span: Span, was_forced: bool },

    /// Represents `#[track_caller]`
    TrackCaller(Span),

    /// Represents `#[type_const]`.
    TypeConst(Span),

    /// Represents `#[type_length_limit]`
    TypeLengthLimit { attr_span: Span, limit_span: Span, limit: Limit },

    /// Represents `#[rustc_unsafe_specialization_marker]`.
    UnsafeSpecializationMarker(Span),

    /// Represents `#[unstable_feature_bound]`.
    UnstableFeatureBound(ThinVec<(Symbol, Span)>),

    /// Represents `#[used]`
    Used { used_by: UsedBy, span: Span },
    // tidy-alphabetical-end
}