Deny ~const trait bounds in inherent impl headers

3 files changed, 17 insertions, 3 deletions

diff --git a/compiler/rustc_ast_passes/messages.ftl b/compiler/rustc_ast_passes/messages.ftl
index 28bd6c2111b..790b583134c 100644
--- a/compiler/rustc_ast_passes/messages.ftl
+++ b/compiler/rustc_ast_passes/messages.ftl
@@ -225,7 +225,8 @@ ast_passes_tilde_const_disallowed = `~const` is not allowed here
     .closure = closures cannot have `~const` trait bounds
     .function = this function is not `const`, so it cannot have `~const` trait bounds
     .trait = this trait is not a `#[const_trait]`, so it cannot have `~const` trait bounds
-    .impl = this impl is not `const`, so it cannot have `~const` trait bounds
+    .trait_impl = this impl is not `const`, so it cannot have `~const` trait bounds
+    .impl = inherent impls cannot have `~const` trait bounds
     .object = trait objects cannot have `~const` trait bounds
     .item = this item cannot have `~const` trait bounds
 
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index 59cf18c2459..326ac459c37 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -41,6 +41,7 @@ enum DisallowTildeConstContext<'a> {
     TraitObject,
     Fn(FnKind<'a>),
     Trait(Span),
+    TraitImpl(Span),
     Impl(Span),
     Item,
 }
@@ -837,7 +838,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     this.visit_vis(&item.vis);
                     this.visit_ident(item.ident);
                     let disallowed = matches!(constness, Const::No)
-                        .then(|| DisallowTildeConstContext::Impl(item.span));
+                        .then(|| DisallowTildeConstContext::TraitImpl(item.span));
                     this.with_tilde_const(disallowed, |this| this.visit_generics(generics));
                     this.visit_trait_ref(t);
                     this.visit_ty(self_ty);
@@ -890,7 +891,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 
                 self.visit_vis(&item.vis);
                 self.visit_ident(item.ident);
-                self.with_tilde_const(None, |this| this.visit_generics(generics));
+                self.with_tilde_const(Some(DisallowTildeConstContext::Impl(item.span)), |this| {
+                    this.visit_generics(generics)
+                });
                 self.visit_ty(self_ty);
                 walk_list!(self, visit_assoc_item, items, AssocCtxt::Impl);
                 walk_list!(self, visit_attribute, &item.attrs);
@@ -1216,7 +1219,12 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                         &DisallowTildeConstContext::Trait(span) => {
                             errors::TildeConstReason::Trait { span }
                         }
+                        &DisallowTildeConstContext::TraitImpl(span) => {
+                            errors::TildeConstReason::TraitImpl { span }
+                        }
                         &DisallowTildeConstContext::Impl(span) => {
+                            // FIXME(effects): Consider providing a help message or even a structured
+                            // suggestion for moving such bounds to the assoc const fns if available.
                             errors::TildeConstReason::Impl { span }
                         }
                         DisallowTildeConstContext::TraitObject => {
diff --git a/compiler/rustc_ast_passes/src/errors.rs b/compiler/rustc_ast_passes/src/errors.rs
index 928bf19759a..4283fc7c07d 100644
--- a/compiler/rustc_ast_passes/src/errors.rs
+++ b/compiler/rustc_ast_passes/src/errors.rs
@@ -563,6 +563,11 @@ pub enum TildeConstReason {
         #[primary_span]
         span: Span,
     },
+    #[note(ast_passes_trait_impl)]
+    TraitImpl {
+        #[primary_span]
+        span: Span,
+    },
     #[note(ast_passes_impl)]
     Impl {
         #[primary_span]