Move check_rustc_pub_transparent into the attribute parser

compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

@@ -541,7 +541,7 @@ impl CombineAttributeParser for TargetFeatureParser {
         parse_tf_attribute(cx, args)
     }
 
-    fn finalize_check(cx: &FinalizeContext<'_, '_>, attr_span: Span) {
+    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 {

compiler/rustc_attr_parsing/src/attributes/link_attrs.rs

@@ -576,7 +576,7 @@ impl NoArgsAttributeParser for FfiPureParser {
     const STABILITY: AttributeStability = unstable!(ffi_pure);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::FfiPure;
 
-    fn finalize_check(cx: &FinalizeContext<'_, '_>, attr_span: Span) {
+    fn finalize_check(cx: &FinalizeCheckContext<'_, '_>, attr_span: Span) {
         // `#[ffi_const]` functions cannot be `#[ffi_pure]`.
         if cx.all_attrs.iter().any(|a| a.word_is(sym::ffi_const)) {
             cx.emit_err(BothFfiConstAndPure { attr_span });

compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs

@@ -1,6 +1,9 @@
 use rustc_feature::AttributeStability;
+use rustc_hir::attrs::ReprAttr;
+use rustc_hir::find_attr;
 
 use super::prelude::*;
+use crate::session_diagnostics::RustcPubTransparent;
 
 pub(crate) struct RustcAsPtrParser;
 impl NoArgsAttributeParser for RustcAsPtrParser {
@@ -26,6 +29,17 @@ impl NoArgsAttributeParser for RustcPubTransparentParser {
     ]);
     const STABILITY: AttributeStability = unstable!(rustc_attrs);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::RustcPubTransparent;
+
+    fn finalize_check(cx: &FinalizeCheckContext<'_, '_>, attr_span: Span) {
+        // `#[rustc_pub_transparent]` may only be applied to `#[repr(transparent)]` types.
+        let is_transparent = find_attr!(
+            cx.parsed_attrs,
+            Repr { reprs, .. } if reprs.iter().any(|(r, _)| r == &ReprAttr::ReprTransparent)
+        );
+        if !is_transparent {
+            cx.emit_err(RustcPubTransparent { span: cx.target_span, attr_span });
+        }
+    }
 }
 
 pub(crate) struct RustcPassByValueParser;

compiler/rustc_attr_parsing/src/attributes/mod.rs

@@ -26,7 +26,7 @@ use rustc_span::edition::Edition;
 use rustc_span::{Span, Symbol};
 use thin_vec::ThinVec;
 
-use crate::context::{AcceptContext, FinalizeContext};
+use crate::context::{AcceptContext, FinalizeCheckContext, FinalizeCheckFn, FinalizeContext};
 use crate::parser::ArgParser;
 use crate::session_diagnostics::UnusedMultiple;
 use crate::target_checking::AllowedTargets;
@@ -117,6 +117,20 @@ pub(crate) trait AttributeParser: Default + 'static {
     /// every single syntax item that could have attributes applied to it.
     /// Your accept mappings should determine whether this returns something.
     fn finalize(self, cx: &FinalizeContext<'_, '_>) -> Option<AttributeKind>;
+
+    /// If this parser produced an attribute, optionally returns a cross-attribute check
+    /// to run once *all* attributes on the item have been finalized, together with the
+    /// span it should be reported at.
+    ///
+    /// Running after finalization means the check can inspect the fully parsed attributes
+    /// via [`FinalizeCheckContext::parsed_attrs`], which are not yet all available during
+    /// [`finalize`](Self::finalize). This is queried right before `finalize` consumes the
+    /// parser state.
+    ///
+    /// Defaults to no check.
+    fn deferred_finalize_check(&self) -> Option<(FinalizeCheckFn, Span)> {
+        None
+    }
 }
 
 /// Alternative to [`AttributeParser`] that automatically handles state management.
@@ -148,13 +162,14 @@ pub(crate) trait SingleAttributeParser: 'static {
     /// Converts a single syntactical attribute to a single semantic attribute, or [`AttributeKind`]
     fn convert(cx: &mut AcceptContext<'_, '_>, args: &ArgParser) -> Option<AttributeKind>;
 
-    /// Optional cross-attribute validation, run once during finalization after all
-    /// attributes on the item have been parsed. Unlike [`convert`](Self::convert), this
-    /// has access to the sibling attributes via [`FinalizeContext::all_attrs`], so it can
-    /// reject incompatible combinations. `attr_span` is the span of this attribute.
+    /// Optional cross-attribute validation, run once *after* all attributes on the item
+    /// have been finalized. Unlike [`convert`](Self::convert), this has access to the
+    /// sibling attributes via [`FinalizeCheckContext::all_attrs`] and the fully parsed
+    /// attributes via [`FinalizeCheckContext::parsed_attrs`], so it can reject incompatible
+    /// combinations. `attr_span` is the span of this attribute.
     ///
     /// Defaults to a no-op.
-    fn finalize_check(_cx: &FinalizeContext<'_, '_>, _attr_span: Span) {}
+    fn finalize_check(_cx: &FinalizeCheckContext<'_, '_>, _attr_span: Span) {}
 }
 
 /// Use in combination with [`SingleAttributeParser`].
@@ -185,11 +200,15 @@ impl<T: SingleAttributeParser> AttributeParser for Single<T> {
     const ALLOWED_TARGETS: AllowedTargets<'_> = T::ALLOWED_TARGETS;
     const SAFETY: AttributeSafety = T::SAFETY;
 
-    fn finalize(self, cx: &FinalizeContext<'_, '_>) -> Option<AttributeKind> {
-        let (kind, span) = self.1?;
-        T::finalize_check(cx, span);
+    fn finalize(self, _cx: &FinalizeContext<'_, '_>) -> Option<AttributeKind> {
+        let (kind, _span) = self.1?;
         Some(kind)
     }
+
+    fn deferred_finalize_check(&self) -> Option<(FinalizeCheckFn, Span)> {
+        let (_, span) = self.1.as_ref()?;
+        Some((<T as SingleAttributeParser>::finalize_check, *span))
+    }
 }
 
 pub(crate) enum OnDuplicate {
@@ -269,13 +288,14 @@ pub(crate) trait NoArgsAttributeParser: 'static {
     /// Create the [`AttributeKind`] given attribute's [`Span`].
     const CREATE: fn(Span) -> AttributeKind;
 
-    /// Optional cross-attribute validation, run once during finalization after all
-    /// attributes on the item have been parsed. Has access to the sibling attributes via
-    /// [`FinalizeContext::all_attrs`], so it can reject incompatible combinations.
+    /// Optional cross-attribute validation, run once *after* all attributes on the item
+    /// have been finalized. Has access to the sibling attributes via
+    /// [`FinalizeCheckContext::all_attrs`] and the fully parsed attributes via
+    /// [`FinalizeCheckContext::parsed_attrs`], so it can reject incompatible combinations.
     /// `attr_span` is the span of this attribute.
     ///
     /// Defaults to a no-op.
-    fn finalize_check(_cx: &FinalizeContext<'_, '_>, _attr_span: Span) {}
+    fn finalize_check(_cx: &FinalizeCheckContext<'_, '_>, _attr_span: Span) {}
 }
 
 pub(crate) struct WithoutArgs<T: NoArgsAttributeParser>(PhantomData<T>);
@@ -299,7 +319,7 @@ impl<T: NoArgsAttributeParser> SingleAttributeParser for WithoutArgs<T> {
         Some(T::CREATE(cx.attr_span))
     }
 
-    fn finalize_check(cx: &FinalizeContext<'_, '_>, attr_span: Span) {
+    fn finalize_check(cx: &FinalizeCheckContext<'_, '_>, attr_span: Span) {
         T::finalize_check(cx, attr_span)
     }
 }
@@ -336,13 +356,14 @@ pub(crate) trait CombineAttributeParser: 'static {
         args: &ArgParser,
     ) -> impl IntoIterator<Item = Self::Item>;
 
-    /// Optional cross-attribute validation, run once during finalization after all
-    /// attributes on the item have been parsed. Has access to the sibling attributes via
-    /// [`FinalizeContext::all_attrs`], so it can reject incompatible combinations.
+    /// Optional cross-attribute validation, run once *after* all attributes on the item
+    /// have been finalized. Has access to the sibling attributes via
+    /// [`FinalizeCheckContext::all_attrs`] and the fully parsed attributes via
+    /// [`FinalizeCheckContext::parsed_attrs`], so it can reject incompatible combinations.
     /// `attr_span` is the span of the first attribute that was encountered.
     ///
     /// Defaults to a no-op.
-    fn finalize_check(_cx: &FinalizeContext<'_, '_>, _attr_span: Span) {}
+    fn finalize_check(_cx: &FinalizeCheckContext<'_, '_>, _attr_span: Span) {}
 }
 
 /// Use in combination with [`CombineAttributeParser`].
@@ -375,12 +396,12 @@ impl<T: CombineAttributeParser> AttributeParser for Combine<T> {
     const ALLOWED_TARGETS: AllowedTargets<'_> = T::ALLOWED_TARGETS;
     const SAFETY: AttributeSafety = T::SAFETY;
 
-    fn finalize(self, cx: &FinalizeContext<'_, '_>) -> Option<AttributeKind> {
-        if let Some(first_span) = self.first_span {
-            T::finalize_check(cx, first_span);
-            Some(T::CONVERT(self.items, first_span))
-        } else {
-            None
-        }
+    fn finalize(self, _cx: &FinalizeContext<'_, '_>) -> Option<AttributeKind> {
+        let first_span = self.first_span?;
+        Some(T::CONVERT(self.items, first_span))
+    }
+
+    fn deferred_finalize_check(&self) -> Option<(FinalizeCheckFn, Span)> {
+        Some((<T as CombineAttributeParser>::finalize_check, self.first_span?))
     }
 }

compiler/rustc_attr_parsing/src/attributes/prelude.rs

@@ -15,7 +15,7 @@ pub(super) use crate::attributes::{
 };
 // contexts
 #[doc(hidden)]
-pub(super) use crate::context::{AcceptContext, FinalizeContext};
+pub(super) use crate::context::{AcceptContext, FinalizeCheckContext, FinalizeContext};
 #[doc(hidden)]
 pub(super) use crate::parser::*;
 // target checking

compiler/rustc_attr_parsing/src/context.rs

@@ -12,8 +12,8 @@ use rustc_ast::{AttrStyle, MetaItemLit, Safety};
 use rustc_data_structures::sync::{DynSend, DynSync};
 use rustc_errors::{Diag, DiagCtxtHandle, Diagnostic, Level, MultiSpan};
 use rustc_feature::AttributeStability;
-use rustc_hir::AttrPath;
 use rustc_hir::attrs::AttributeKind;
+use rustc_hir::{AttrPath, Attribute};
 use rustc_parse::parser::Recovery;
 use rustc_session::Session;
 use rustc_session::lint::{Lint, LintId};
@@ -94,7 +94,24 @@ pub(super) struct GroupTypeInnerAccept {
 
 pub(crate) type AcceptFn =
     Box<dyn for<'sess> Fn(&mut AcceptContext<'_, 'sess>, &ArgParser) + Send + Sync>;
-pub(crate) type FinalizeFn = fn(&mut FinalizeContext<'_, '_>) -> Option<AttributeKind>;
+
+pub(crate) type FinalizeFn = fn(&mut FinalizeContext<'_, '_>) -> FinalizeOutput;
+
+/// A cross-attribute check that runs *after* all attributes on an item have been
+/// finalized, so it can inspect the fully parsed attributes via
+/// [`FinalizeCheckContext::parsed_attrs`]. The [`Span`] is the span of the attribute the
+/// check is associated with, used for diagnostics.
+pub(crate) type FinalizeCheckFn = fn(&FinalizeCheckContext<'_, '_>, Span);
+
+/// The result of finalizing a single attribute parser.
+pub(crate) struct FinalizeOutput {
+    /// The attribute the parser produced, if any.
+    pub(crate) attr: Option<AttributeKind>,
+    /// A check to run once *all* attributes on the item have been finalized, together
+    /// with the span it should be reported at. Deferred so that it can inspect the fully
+    /// parsed attributes via [`FinalizeCheckContext::parsed_attrs`].
+    pub(crate) deferred_check: Option<(FinalizeCheckFn, Span)>,
+}
 
 macro_rules! attribute_parsers {
     (
@@ -123,7 +140,11 @@ macro_rules! attribute_parsers {
                                     allowed_targets: <$names as crate::attributes::AttributeParser>::ALLOWED_TARGETS,
                                     finalizer: |cx| {
                                         let state = STATE_OBJECT.take();
-                                        state.finalize(cx)
+                                        // Compute the deferred check (if any) before consuming
+                                        // the state in `finalize`.
+                                        let deferred_check = state.deferred_finalize_check();
+                                        let attr = state.finalize(cx);
+                                        FinalizeOutput { attr, deferred_check }
                                     }
                                 });
                             }
@@ -792,6 +813,42 @@ impl<'p, 'sess: 'p> DerefMut for FinalizeContext<'p, 'sess> {
     }
 }
 
+/// Context given to deferred cross-attribute checks (`finalize_check`).
+///
+/// These checks run *after* every attribute on an item has been finalized, so unlike
+/// [`FinalizeContext`] this context can also inspect the fully parsed attributes via
+/// [`parsed_attrs`](Self::parsed_attrs).
+pub(crate) struct FinalizeCheckContext<'p, 'sess> {
+    pub(crate) shared: SharedContext<'p, 'sess>,
+
+    /// A list of all attribute on this syntax node.
+    ///
+    /// Useful for compatibility checks with other attributes.
+    ///
+    /// Unlike [`parsed_attrs`](Self::parsed_attrs), this only contains the *paths* of the
+    /// attributes.
+    pub(crate) all_attrs: &'p [RefPathParser<'p>],
+
+    /// All attributes that have been parsed on this syntax node.
+    ///
+    /// Unlike [`all_attrs`](Self::all_attrs), this contains the fully parsed attributes.
+    pub(crate) parsed_attrs: &'p [Attribute],
+}
+
+impl<'p, 'sess: 'p> Deref for FinalizeCheckContext<'p, 'sess> {
+    type Target = SharedContext<'p, 'sess>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.shared
+    }
+}
+
+impl<'p, 'sess: 'p> DerefMut for FinalizeCheckContext<'p, 'sess> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.shared
+    }
+}
+
 impl<'p, 'sess: 'p> Deref for SharedContext<'p, 'sess> {
     type Target = AttributeParser<'sess>;
 

compiler/rustc_attr_parsing/src/interface.rs

@@ -18,7 +18,8 @@ use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, Symbol, sym};
 
 use crate::attributes::AttributeSafety;
 use crate::context::{
-    ATTRIBUTE_PARSERS, AcceptContext, FinalizeContext, FinalizeFn, SharedContext,
+    ATTRIBUTE_PARSERS, AcceptContext, FinalizeCheckContext, FinalizeCheckFn, FinalizeContext,
+    FinalizeFn, FinalizeOutput, SharedContext,
 };
 use crate::parser::{AllowExprMetavar, ArgParser, PathParser, RefPathParser};
 use crate::session_diagnostics::ParsedDescription;
@@ -448,8 +449,14 @@ impl<'sess> AttributeParser<'sess> {
         }
 
         synthetic_attr_state.finalize_synthetic_attrs(&mut attributes);
+
+        // First, run all finalizers to produce the parsed attributes. Cross-attribute
+        // checks that need to inspect the fully parsed attributes are deferred until all
+        // finalizers have run (see below), since the parsed attributes are not yet all
+        // available here.
+        let mut deferred_checks: Vec<(FinalizeCheckFn, Span)> = Vec::new();
         for f in &finalizers {
-            if let Some(attr) = f(&mut FinalizeContext {
+            let FinalizeOutput { attr, deferred_check } = f(&mut FinalizeContext {
                 shared: SharedContext {
                     cx: self,
                     target_span,
@@ -459,9 +466,33 @@ impl<'sess> AttributeParser<'sess> {
                     has_lint_been_emitted: AtomicBool::new(false),
                 },
                 all_attrs: &attr_paths,
-            }) {
+            });
+            if let Some(attr) = attr {
                 attributes.push(Attribute::Parsed(attr));
             }
+            if let Some(deferred_check) = deferred_check {
+                deferred_checks.push(deferred_check);
+            }
+        }
+
+        // Now that all attributes have been parsed, run the deferred checks. These can
+        // inspect the fully parsed attributes via `FinalizeCheckContext::parsed_attrs`.
+        for (check, attr_span) in deferred_checks {
+            check(
+                &FinalizeCheckContext {
+                    shared: SharedContext {
+                        cx: self,
+                        target_span,
+                        target,
+                        emit_lint: &mut emit_lint,
+                        #[cfg(debug_assertions)]
+                        has_lint_been_emitted: AtomicBool::new(false),
+                    },
+                    all_attrs: &attr_paths,
+                    parsed_attrs: &attributes,
+                },
+                attr_span,
+            );
         }
 
         if !matches!(self.should_emit, ShouldEmit::Nothing) && target == Target::WherePredicate {

compiler/rustc_attr_parsing/src/session_diagnostics.rs

@@ -20,6 +20,15 @@ pub(crate) struct BothFfiConstAndPure {
     pub attr_span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag("attribute should be applied to `#[repr(transparent)]` types")]
+pub(crate) struct RustcPubTransparent {
+    #[primary_span]
+    pub attr_span: Span,
+    #[label("not a `#[repr(transparent)]` type")]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag("{$attr_str} attribute cannot have empty value")]
 pub(crate) struct DocAliasEmpty<'a> {

compiler/rustc_passes/src/check_attr.rs

@@ -207,9 +207,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             AttributeKind::RustcDumpObjectLifetimeDefaults => {
                 self.check_dump_object_lifetime_defaults(hir_id);
             }
-            &AttributeKind::RustcPubTransparent(attr_span) => {
-                self.check_rustc_pub_transparent(attr_span, span, attrs)
-            }
             AttributeKind::Naked(..) => self.check_naked(hir_id, target),
             AttributeKind::TrackCaller(attr_span) => {
                 self.check_track_caller(hir_id, *attr_span, attrs, target)
@@ -386,6 +383,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             AttributeKind::RustcPassIndirectlyInNonRusticAbis(..) => (),
             AttributeKind::RustcPreserveUbChecks => (),
             AttributeKind::RustcProcMacroDecls => (),
+            AttributeKind::RustcPubTransparent(..) => (),
             AttributeKind::RustcReallocator => (),
             AttributeKind::RustcRegions => (),
             AttributeKind::RustcReservationImpl(..) => (),
@@ -1592,14 +1590,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_rustc_pub_transparent(&self, attr_span: Span, span: Span, attrs: &[Attribute]) {
-        if !find_attr!(attrs, Repr { reprs, .. } => reprs.iter().any(|(r, _)| r == &ReprAttr::ReprTransparent))
-            .unwrap_or(false)
-        {
-            self.dcx().emit_err(diagnostics::RustcPubTransparent { span, attr_span });
-        }
-    }
-
     fn check_rustc_force_inline(&self, hir_id: HirId, attrs: &[Attribute], target: Target) {
         if let (Target::Closure, None) = (
             target,