Merge pull request #20032 from lnicola/sync-from-rust

minor: Sync from downstream

4 files changed, 92 insertions, 34 deletions

diff --git a/compiler/rustc_attr_data_structures/src/attributes.rs b/compiler/rustc_attr_data_structures/src/attributes.rs
index d2d1285b075..8f95a017809 100644
--- a/compiler/rustc_attr_data_structures/src/attributes.rs
+++ b/compiler/rustc_attr_data_structures/src/attributes.rs
@@ -57,14 +57,6 @@ impl OptimizeAttr {
     }
 }
 
-#[derive(Clone, Debug, Encodable, Decodable, HashStable_Generic, PrintAttribute)]
-pub enum DiagnosticAttribute {
-    // tidy-alphabetical-start
-    DoNotRecommend,
-    OnUnimplemented,
-    // tidy-alphabetical-end
-}
-
 #[derive(PartialEq, Debug, Encodable, Decodable, Copy, Clone, HashStable_Generic, PrintAttribute)]
 pub enum ReprAttr {
     ReprInt(IntType),
@@ -138,62 +130,107 @@ impl Deprecation {
     }
 }
 
-/// Represent parsed, *built in*, inert attributes.
+/// 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 contains all the information and
+/// structure relevant for the specific attribute.
 ///
-/// That means attributes that are not actually ever expanded.
-/// For more information on this, see the module docs on the [`rustc_attr_parsing`] crate.
-/// They're instead used as markers, to guide the compilation process in various way in most every stage of the compiler.
-/// These are kept around after the AST, into the HIR and further on.
+/// 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.
 ///
-/// The word "parsed" could be a little misleading here, because the parser already parses
-/// attributes early on. However, the result, an [`ast::Attribute`]
-/// is only parsed at a high level, still containing a token stream in many cases. That is
-/// because the structure of the contents varies from attribute to attribute.
-/// With a parsed attribute I mean that each attribute is processed individually into a
-/// final structure, which on-site (the place where the attribute is useful for, think the
-/// the place where `must_use` is checked) little to no extra parsing or validating needs to
-/// happen.
+/// ## 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]`)
 ///
-/// For more docs, look in [`rustc_attr_parsing`].
+/// ## 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 `#[rustc_allow_const_fn_unstable]`.
     AllowConstFnUnstable(ThinVec<Symbol>),
+
+    /// Represents `#[allow_internal_unstable]`.
     AllowInternalUnstable(ThinVec<(Symbol, Span)>),
+
+    /// Represents `#[rustc_as_ptr]` (used by the `dangling_pointers_from_temporaries` lint).
+    AsPtr(Span),
+
+    /// Represents `#[rustc_default_body_unstable]`.
     BodyStability {
         stability: DefaultBodyStability,
         /// Span of the `#[rustc_default_body_unstable(...)]` attribute
         span: Span,
     },
+
+    /// Represents `#[rustc_confusables]`.
     Confusables {
         symbols: ThinVec<Symbol>,
         // FIXME(jdonszelmann): remove when target validation code is moved
         first_span: 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,
-    Deprecation {
-        deprecation: Deprecation,
-        span: Span,
-    },
-    Diagnostic(DiagnosticAttribute),
-    DocComment {
-        style: AttrStyle,
-        kind: CommentKind,
-        span: Span,
-        comment: Symbol,
-    },
+
+    /// Represents [`#[deprecated]`](https://doc.rust-lang.org/stable/reference/attributes/diagnostics.html#the-deprecated-attribute).
+    Deprecation { deprecation: Deprecation, span: 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_macro_transparency]`.
     MacroTransparency(Transparency),
+
+    /// Represents [`#[repr]`](https://doc.rust-lang.org/stable/reference/type-layout.html#representations).
     Repr(ThinVec<(ReprAttr, Span)>),
+
+    /// Represents `#[stable]`, `#[unstable]` and `#[rustc_allowed_through_unstable_modules]`.
     Stability {
         stability: Stability,
-        /// Span of the `#[stable(...)]` or `#[unstable(...)]` attribute
+        /// Span of the attribute.
         span: Span,
     },
     // tidy-alphabetical-end
diff --git a/compiler/rustc_attr_data_structures/src/lib.rs b/compiler/rustc_attr_data_structures/src/lib.rs
index dbfc95b047a..f8355be09ad 100644
--- a/compiler/rustc_attr_data_structures/src/lib.rs
+++ b/compiler/rustc_attr_data_structures/src/lib.rs
@@ -1,3 +1,7 @@
+//! Data structures for representing parsed attributes in the Rust compiler.
+//! For detailed documentation about attribute processing,
+//! see [rustc_attr_parsing](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_attr_parsing/index.html).
+
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![doc(rust_logo)]
@@ -8,6 +12,8 @@ mod attributes;
 mod stability;
 mod version;
 
+pub mod lints;
+
 use std::num::NonZero;
 
 pub use attributes::*;
diff --git a/compiler/rustc_attr_data_structures/src/lints.rs b/compiler/rustc_attr_data_structures/src/lints.rs
new file mode 100644
index 00000000000..7e3664b2263
--- /dev/null
+++ b/compiler/rustc_attr_data_structures/src/lints.rs
@@ -0,0 +1,14 @@
+use rustc_macros::HashStable_Generic;
+use rustc_span::Span;
+
+#[derive(Clone, Debug, HashStable_Generic)]
+pub struct AttributeLint<Id> {
+    pub id: Id,
+    pub span: Span,
+    pub kind: AttributeLintKind,
+}
+
+#[derive(Clone, Debug, HashStable_Generic)]
+pub enum AttributeLintKind {
+    UnusedDuplicate { this: Span, other: Span, warning: bool },
+}
diff --git a/compiler/rustc_attr_data_structures/src/stability.rs b/compiler/rustc_attr_data_structures/src/stability.rs
index c0ca08a60f8..218e771c745 100644
--- a/compiler/rustc_attr_data_structures/src/stability.rs
+++ b/compiler/rustc_attr_data_structures/src/stability.rs
@@ -132,6 +132,7 @@ pub enum StabilityLevel {
         /// fn foobar() {}
         /// ```
         implied_by: Option<Symbol>,
+        old_name: Option<Symbol>,
     },
     /// `#[stable]`
     Stable {