Rewrite empty attribute lint

JonathanBrouwer · JonathanBrouwer · commit bdb57ed42235 · 2025-06-30T19:17:21.000+02:00
Signed-off-by: Jonathan Brouwer &lt;jonathantbrouwer@gmail.com&gt;
diff --git a/compiler/rustc_attr_data_structures/src/attributes.rs b/compiler/rustc_attr_data_structures/src/attributes.rs
@@ -67,8 +67,6 @@ pub enum ReprAttr {
     ReprSimd,
     ReprTransparent,
     ReprAlign(Align),
-    // this one is just so we can emit a lint for it
-    ReprEmpty,
 }
 pub use ReprAttr::*;
 
@@ -201,7 +199,7 @@ pub enum AttributeKind {
     AllowConstFnUnstable(ThinVec<Symbol>),
 
     /// Represents `#[allow_internal_unstable]`.
-    AllowInternalUnstable(ThinVec<(Symbol, Span)>),
+    AllowInternalUnstable(ThinVec<(Symbol, Span)>, Span),
 
     /// Represents `#[rustc_as_ptr]` (used by the `dangling_pointers_from_temporaries` lint).
     AsPtr(Span),
@@ -285,7 +283,7 @@ pub enum AttributeKind {
     PubTransparent(Span),
 
     /// Represents [`#[repr]`](https://doc.rust-lang.org/stable/reference/type-layout.html#representations).
-    Repr(ThinVec<(ReprAttr, Span)>),
+    Repr(ThinVec<(ReprAttr, Span)>, Span),
 
     /// Represents `#[rustc_skip_during_method_dispatch]`.
     SkipDuringMethodDispatch { array: bool, boxed_slice: bool, span: Span },
diff --git a/compiler/rustc_attr_data_structures/src/lints.rs b/compiler/rustc_attr_data_structures/src/lints.rs
@@ -12,4 +12,5 @@ pub struct AttributeLint<Id> {
 pub enum AttributeLintKind {
     UnusedDuplicate { this: Span, other: Span, warning: bool },
     IllFormedAttributeInput { suggestions: Vec<String> },
+    EmptyAttribute { span: Span },
 }
diff --git a/compiler/rustc_attr_parsing/messages.ftl b/compiler/rustc_attr_parsing/messages.ftl
@@ -6,6 +6,10 @@ attr_parsing_deprecated_item_suggestion =
     .help = add `#![feature(deprecated_suggestion)]` to the crate root
     .note = see #94785 for more details
 
+attr_parsing_empty_attribute =
+    unused attribute
+    .suggestion = remove this attribute
+
 attr_parsing_empty_confusables =
     expected at least one confusable name
 attr_parsing_expected_one_cfg_pattern =
diff --git a/compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs b/compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs
@@ -13,7 +13,8 @@ pub(crate) struct AllowInternalUnstableParser;
 impl<S: Stage> CombineAttributeParser<S> for AllowInternalUnstableParser {
     const PATH: &[Symbol] = &[sym::allow_internal_unstable];
     type Item = (Symbol, Span);
-    const CONVERT: ConvertFn<Self::Item> = AttributeKind::AllowInternalUnstable;
+    const CONVERT: ConvertFn<Self::Item> =
+        ConvertFn::WithFirstAttributeSpan(AttributeKind::AllowInternalUnstable);
     const TEMPLATE: AttributeTemplate = template!(Word, List: "feat1, feat2, ...");
 
     fn extend<'c>(
@@ -30,7 +31,7 @@ pub(crate) struct AllowConstFnUnstableParser;
 impl<S: Stage> CombineAttributeParser<S> for AllowConstFnUnstableParser {
     const PATH: &[Symbol] = &[sym::rustc_allow_const_fn_unstable];
     type Item = Symbol;
-    const CONVERT: ConvertFn<Self::Item> = AttributeKind::AllowConstFnUnstable;
+    const CONVERT: ConvertFn<Self::Item> = ConvertFn::Simple(AttributeKind::AllowConstFnUnstable);
     const TEMPLATE: AttributeTemplate = template!(Word, List: "feat1, feat2, ...");
 
     fn extend<'c>(
diff --git a/compiler/rustc_attr_parsing/src/attributes/mod.rs b/compiler/rustc_attr_parsing/src/attributes/mod.rs
@@ -228,7 +228,10 @@ pub(crate) enum AttributeOrder {
     KeepLast,
 }
 
-type ConvertFn<E> = fn(ThinVec<E>) -> AttributeKind;
+pub(crate) enum ConvertFn<E> {
+    Simple(fn(ThinVec<E>) -> AttributeKind),
+    WithFirstAttributeSpan(fn(ThinVec<E>, Span) -> AttributeKind),
+}
 
 /// Alternative to [`AttributeParser`] that automatically handles state management.
 /// If multiple attributes appear on an element, combines the values of each into a
@@ -262,22 +265,36 @@ pub(crate) trait CombineAttributeParser<S: Stage>: 'static {
 pub(crate) struct Combine<T: CombineAttributeParser<S>, S: Stage>(
     PhantomData<(S, T)>,
     ThinVec<<T as CombineAttributeParser<S>>::Item>,
+    Option<Span>,
 );
 
 impl<T: CombineAttributeParser<S>, S: Stage> Default for Combine<T, S> {
     fn default() -> Self {
-        Self(Default::default(), Default::default())
+        Self(Default::default(), Default::default(), Default::default())
     }
 }
 
 impl<T: CombineAttributeParser<S>, S: Stage> AttributeParser<S> for Combine<T, S> {
     const ATTRIBUTES: AcceptMapping<Self, S> = &[(
         T::PATH,
         <T as CombineAttributeParser<S>>::TEMPLATE,
-        |group: &mut Combine<T, S>, cx, args| group.1.extend(T::extend(cx, args)),
+        |group: &mut Combine<T, S>, cx, args| {
+            // Keep track of the span of the first attribute, for diagnostics
+            if group.2.is_none() {
+                group.2 = Some(cx.attr_span);
+            }
+            group.1.extend(T::extend(cx, args))
+        },
     )];
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
-        if self.1.is_empty() { None } else { Some(T::CONVERT(self.1)) }
+        if let Some(first_span) = self.2 {
+            Some(match T::CONVERT {
+                ConvertFn::Simple(f) => f(self.1),
+                ConvertFn::WithFirstAttributeSpan(f) => f(self.1, first_span),
+            })
+        } else {
+            None
+        }
     }
 }
diff --git a/compiler/rustc_attr_parsing/src/attributes/repr.rs b/compiler/rustc_attr_parsing/src/attributes/repr.rs
@@ -23,7 +23,7 @@ pub(crate) struct ReprParser;
 impl<S: Stage> CombineAttributeParser<S> for ReprParser {
     type Item = (ReprAttr, Span);
     const PATH: &[Symbol] = &[sym::repr];
-    const CONVERT: ConvertFn<Self::Item> = AttributeKind::Repr;
+    const CONVERT: ConvertFn<Self::Item> = ConvertFn::WithFirstAttributeSpan(AttributeKind::Repr);
     // FIXME(jdonszelmann): never used
     const TEMPLATE: AttributeTemplate =
         template!(List: "C | Rust | align(...) | packed(...) | <integer type> | transparent");
@@ -40,8 +40,8 @@ impl<S: Stage> CombineAttributeParser<S> for ReprParser {
         };
 
         if list.is_empty() {
-            // this is so validation can emit a lint
-            reprs.push((ReprAttr::ReprEmpty, cx.attr_span));
+            cx.warn_empty_attribute(cx.attr_span);
+            return reprs;
         }
 
         for param in list.mixed() {
diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
@@ -147,6 +147,7 @@ mod private {
 #[allow(private_interfaces)]
 pub trait Stage: Sized + 'static + Sealed {
     type Id: Copy;
+    const SHOULD_EMIT_LINTS: bool;
 
     fn parsers() -> &'static group_type!(Self);
 
@@ -157,6 +158,7 @@ pub trait Stage: Sized + 'static + Sealed {
 #[allow(private_interfaces)]
 impl Stage for Early {
     type Id = NodeId;
+    const SHOULD_EMIT_LINTS: bool = false;
 
     fn parsers() -> &'static group_type!(Self) {
         &early::ATTRIBUTE_PARSERS
@@ -170,6 +172,7 @@ impl Stage for Early {
 #[allow(private_interfaces)]
 impl Stage for Late {
     type Id = HirId;
+    const SHOULD_EMIT_LINTS: bool = true;
 
     fn parsers() -> &'static group_type!(Self) {
         &late::ATTRIBUTE_PARSERS
@@ -210,6 +213,9 @@ impl<'f, 'sess: 'f, S: Stage> SharedContext<'f, 'sess, S> {
     /// must be delayed until after HIR is built. This method will take care of the details of
     /// that.
     pub(crate) fn emit_lint(&mut self, lint: AttributeLintKind, span: Span) {
+        if !S::SHOULD_EMIT_LINTS {
+            return;
+        }
         let id = self.target_id;
         (self.emit_lint)(AttributeLint { id, span, kind: lint });
     }
@@ -381,6 +387,10 @@ impl<'f, 'sess: 'f, S: Stage> AcceptContext<'f, 'sess, S> {
             },
         })
     }
+
+    pub(crate) fn warn_empty_attribute(&mut self, span: Span) {
+        self.emit_lint(AttributeLintKind::EmptyAttribute { span }, span);
+    }
 }
 
 impl<'f, 'sess, S: Stage> Deref for AcceptContext<'f, 'sess, S> {
diff --git a/compiler/rustc_attr_parsing/src/lints.rs b/compiler/rustc_attr_parsing/src/lints.rs
@@ -28,5 +28,11 @@ pub fn emit_attribute_lint<L: LintEmitter>(lint: &AttributeLint<HirId>, lint_emi
                 },
             );
         }
+        AttributeLintKind::EmptyAttribute { span } => lint_emitter.emit_node_span_lint(
+            rustc_session::lint::builtin::UNUSED_ATTRIBUTES,
+            *id,
+            *span,
+            session_diagnostics::EmptyAttributeList { attr_span: *span },
+        ),
     }
 }
diff --git a/compiler/rustc_attr_parsing/src/session_diagnostics.rs b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
@@ -466,6 +466,13 @@ pub(crate) struct EmptyConfusables {
     pub span: Span,
 }
 
+#[derive(LintDiagnostic)]
+#[diag(attr_parsing_empty_attribute)]
+pub(crate) struct EmptyAttributeList {
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub attr_span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(attr_parsing_invalid_alignment_value, code = E0589)]
 pub(crate) struct InvalidAlignmentValue {
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -485,7 +485,7 @@ impl<'a> TraitDef<'a> {
             Annotatable::Item(item) => {
                 let is_packed = matches!(
                     AttributeParser::parse_limited(cx.sess, &item.attrs, sym::repr, item.span, item.id),
-                    Some(Attribute::Parsed(AttributeKind::Repr(r))) if r.iter().any(|(x, _)| matches!(x, ReprPacked(..)))
+                    Some(Attribute::Parsed(AttributeKind::Repr(r, _))) if r.iter().any(|(x, _)| matches!(x, ReprPacked(..)))
                 );
 
                 let newitem = match &item.kind {
diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
@@ -109,7 +109,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
 
         if let hir::Attribute::Parsed(p) = attr {
             match p {
-                AttributeKind::Repr(reprs) => {
+                AttributeKind::Repr(reprs, _) => {
                     codegen_fn_attrs.alignment = reprs
                         .iter()
                         .filter_map(
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
@@ -880,7 +880,7 @@ impl SyntaxExtension {
         is_local: bool,
     ) -> SyntaxExtension {
         let allow_internal_unstable =
-            find_attr!(attrs, AttributeKind::AllowInternalUnstable(i) => i)
+            find_attr!(attrs, AttributeKind::AllowInternalUnstable(i, _) => i)
                 .map(|i| i.as_slice())
                 .unwrap_or_default();
         // FIXME(jdonszelman): allow_internal_unsafe isn't yet new-style
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -1224,7 +1224,7 @@ pub(super) fn check_packed(tcx: TyCtxt<'_>, sp: Span, def: ty::AdtDef<'_>) {
     let repr = def.repr();
     if repr.packed() {
         if let Some(reprs) =
-            attrs::find_attr!(tcx.get_all_attrs(def.did()), attrs::AttributeKind::Repr(r) => r)
+            attrs::find_attr!(tcx.get_all_attrs(def.did()), attrs::AttributeKind::Repr(r, _) => r)
         {
             for (r, _) in reprs {
                 if let ReprPacked(pack) = r
@@ -1447,7 +1447,7 @@ fn check_enum(tcx: TyCtxt<'_>, def_id: LocalDefId) {
     if def.variants().is_empty() {
         attrs::find_attr!(
             tcx.get_all_attrs(def_id),
-            attrs::AttributeKind::Repr(rs) => {
+            attrs::AttributeKind::Repr(rs, _) => {
                 struct_span_code_err!(
                     tcx.dcx(),
                     rs.first().unwrap().1,
diff --git a/compiler/rustc_lint/src/nonstandard_style.rs b/compiler/rustc_lint/src/nonstandard_style.rs
@@ -168,7 +168,7 @@ impl EarlyLintPass for NonCamelCaseTypes {
     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
         let has_repr_c = matches!(
             AttributeParser::parse_limited(cx.sess(), &it.attrs, sym::repr, it.span, it.id),
-            Some(Attribute::Parsed(AttributeKind::Repr(r))) if r.iter().any(|(r, _)| r == &ReprAttr::ReprC)
+            Some(Attribute::Parsed(AttributeKind::Repr(r, _))) if r.iter().any(|(r, _)| r == &ReprAttr::ReprC)
         );
 
         if has_repr_c {
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
@@ -1521,7 +1521,8 @@ impl<'tcx> TyCtxt<'tcx> {
             field_shuffle_seed ^= user_seed;
         }
 
-        if let Some(reprs) = attr::find_attr!(self.get_all_attrs(did), AttributeKind::Repr(r) => r)
+        if let Some(reprs) =
+            attr::find_attr!(self.get_all_attrs(did), AttributeKind::Repr(r, _) => r)
         {
             for (r, _) in reprs {
                 flags.insert(match *r {
@@ -1562,10 +1563,6 @@ impl<'tcx> TyCtxt<'tcx> {
                         max_align = max_align.max(Some(align));
                         ReprFlags::empty()
                     }
-                    attr::ReprEmpty => {
-                        /* skip these, they're just for diagnostics */
-                        ReprFlags::empty()
-                    }
                 });
             }
         }
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
diff --git a/src/tools/clippy/clippy_lints/src/attrs/repr_attributes.rs b/src/tools/clippy/clippy_lints/src/attrs/repr_attributes.rs
diff --git a/src/tools/clippy/clippy_lints/src/default_union_representation.rs b/src/tools/clippy/clippy_lints/src/default_union_representation.rs
diff --git a/tests/ui/empty/empty-attributes.stderr b/tests/ui/empty/empty-attributes.stderr
diff --git a/tests/ui/repr/repr-empty-packed.stderr b/tests/ui/repr/repr-empty-packed.stderr

Original file line number	Diff line number	Diff line change
`@@ -12,4 +12,5 @@ pub struct AttributeLint<Id> {`
`12`	`12`	`pub enum AttributeLintKind {`
`13`	`13`	`UnusedDuplicate { this: Span, other: Span, warning: bool },`
`14`	`14`	`IllFormedAttributeInput { suggestions: Vec<String> },`
	`15`	`+ EmptyAttribute { span: Span },`
`15`	`16`	`}`
Original file line number	Diff line number	Diff line change
`@@ -28,5 +28,11 @@ pub fn emit_attribute_lint<L: LintEmitter>(lint: &AttributeLint<HirId>, lint_emi`
`28`	`28`	`},`
`29`	`29`	`);`
`30`	`30`	`}`
	`31`	`+ AttributeLintKind::EmptyAttribute { span } => lint_emitter.emit_node_span_lint(`
	`32`	`+ rustc_session::lint::builtin::UNUSED_ATTRIBUTES,`
	`33`	`+ *id,`
	`34`	`+ *span,`
	`35`	`+ session_diagnostics::EmptyAttributeList { attr_span: *span },`
	`36`	`+ ),`
`31`	`37`	`}`
`32`	`38`	`}`