Restrict the set of things that const stability can be applied to

compiler/rustc_attr_parsing/src/attributes/stability.rs

@@ -244,7 +244,20 @@ impl<S: Stage> AttributeParser<S> for ConstStabilityParser {
             this.promotable = true;
         }),
     ];
-    const ALLOWED_TARGETS: AllowedTargets = ALLOWED_TARGETS;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Impl { of_trait: false }),
+        Allow(Target::Impl { of_trait: true }),
+        Allow(Target::Use), // FIXME I don't think this does anything?
+        Allow(Target::Const),
+        Allow(Target::AssocConst),
+        Allow(Target::Trait),
+        Allow(Target::Static),
+        Allow(Target::Crate),
+    ]);
 
     fn finalize(mut self, cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         if self.promotable {

compiler/rustc_expand/src/base.rs

@@ -962,15 +962,6 @@ impl SyntaxExtension {
 
         let stability = find_attr!(attrs, AttributeKind::Stability { stability, .. } => *stability);
 
-        // FIXME(jdonszelmann): make it impossible to miss the or_else in the typesystem
-        if let Some(sp) =
-            find_attr!(attrs, AttributeKind::RustcConstStability { span, .. } => *span)
-        {
-            sess.dcx().emit_err(errors::MacroConstStability {
-                span: sp,
-                head_span: sess.source_map().guess_head_span(span),
-            });
-        }
         if let Some(sp) = find_attr!(attrs, AttributeKind::RustcBodyStability{ span, .. } => *span)
         {
             sess.dcx().emit_err(errors::MacroBodyStability {

compiler/rustc_expand/src/errors.rs

@@ -80,16 +80,6 @@ pub(crate) struct ResolveRelativePath {
     pub path: String,
 }
 
-#[derive(Diagnostic)]
-#[diag("macros cannot have const stability attributes")]
-pub(crate) struct MacroConstStability {
-    #[primary_span]
-    #[label("invalid const stability attribute")]
-    pub span: Span,
-    #[label("const stability attribute affects this macro")]
-    pub head_span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag("macros cannot have body stability attributes")]
 pub(crate) struct MacroBodyStability {

library/core/src/array/drain.rs

@@ -31,7 +31,6 @@ impl<'l, 'f, T, U, const N: usize, F: FnMut(T) -> U> Drain<'l, 'f, T, N, F> {
 }
 
 /// See [`Drain::new`]; this is our fake iterator.
-#[rustc_const_unstable(feature = "array_try_map", issue = "79711")]
 #[unstable(feature = "array_try_map", issue = "79711")]
 pub(super) struct Drain<'l, 'f, T, const N: usize, F> {
     // FIXME(const-hack): This is essentially a slice::IterMut<'static>, replace when possible.

tests/ui/attributes/const-stability-on-macro.rs

@@ -2,13 +2,13 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 #[rustc_const_stable(feature = "foo", since = "3.3.3")]
-//~^ ERROR macros cannot have const stability attributes
+//~^ ERROR attribute cannot be used on macro defs
 macro_rules! foo {
     () => {};
 }
 
-#[rustc_const_unstable(feature = "bar", issue="none")]
-//~^ ERROR macros cannot have const stability attributes
+#[rustc_const_unstable(feature = "bar", issue = "none")]
+//~^ ERROR attribute cannot be used on macro defs
 macro_rules! bar {
     () => {};
 }

tests/ui/attributes/const-stability-on-macro.stderr

@@ -1,20 +1,18 @@
-error: macros cannot have const stability attributes
+error: `#[rustc_const_stable]` attribute cannot be used on macro defs
   --> $DIR/const-stability-on-macro.rs:4:1
    |
 LL | #[rustc_const_stable(feature = "foo", since = "3.3.3")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid const stability attribute
-LL |
-LL | macro_rules! foo {
-   | ---------------- const stability attribute affects this macro
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: `#[rustc_const_stable]` can be applied to associated consts, constants, crates, functions, impl blocks, statics, traits, and use statements
 
-error: macros cannot have const stability attributes
+error: `#[rustc_const_unstable]` attribute cannot be used on macro defs
   --> $DIR/const-stability-on-macro.rs:10:1
    |
-LL | #[rustc_const_unstable(feature = "bar", issue="none")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid const stability attribute
-LL |
-LL | macro_rules! bar {
-   | ---------------- const stability attribute affects this macro
+LL | #[rustc_const_unstable(feature = "bar", issue = "none")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: `#[rustc_const_unstable]` can be applied to associated consts, constants, crates, functions, impl blocks, statics, traits, and use statements
 
 error: aborting due to 2 previous errors