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diagnostics: avoid ICE for undeclared generic parameter in impl #154182

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diagnostics: avoid ICE for undeclared generic parameter in impl #154182

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2 changes: 1 addition & 1 deletion compiler/rustc_resolve/src/late/diagnostics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3381,7 +3381,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
&& def_id.is_local()
&& let Some(local_def_id) = def_id.as_local()
&& let Some(struct_generics) = self.r.struct_generics.get(&local_def_id)
&& let target_param = &struct_generics.params[idx]
&& let Some(target_param) = &struct_generics.params.get(idx)
&& let GenericParamKind::Const { ty, .. } = &target_param.kind
&& let TyKind::Path(_, path) = &ty.kind
{
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5 changes: 5 additions & 0 deletions tests/ui/missing/undeclared-generic-parameter.rs
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@@ -0,0 +1,5 @@
struct A;
impl A<B> {}
//~^ ERROR cannot find type `B` in this scope
//~| ERROR struct takes 0 generic arguments but 1 generic argument was supplied
fn main() {}
36 changes: 36 additions & 0 deletions tests/ui/missing/undeclared-generic-parameter.stderr
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@@ -0,0 +1,36 @@
error[E0425]: cannot find type `B` in this scope
--> $DIR/undeclared-generic-parameter.rs:2:8
|
LL | struct A;
| --------- similarly named struct `A` defined here
LL | impl A<B> {}
| ^
|
help: a struct with a similar name exists
|
LL - impl A<B> {}
LL + impl A<A> {}
|
help: you might be missing a type parameter
|
LL | impl<B> A<B> {}
| +++
Comment on lines +1 to +17
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@estebank estebank Mar 21, 2026 •
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(Not for this PR) It'd be nice if we didn't provide any suggestion in this case and instead mentioned that A takes no parameter (at this place, same thing for struct A<T> and impl<T> A<T, K> {} so that we emit a single error instead of two, but this is [p-low].


error[E0107]: struct takes 0 generic arguments but 1 generic argument was supplied
--> $DIR/undeclared-generic-parameter.rs:2:6
|
LL | impl A<B> {}
| ^--- help: remove the unnecessary generics
| |
| expected 0 generic arguments
|
note: struct defined here, with 0 generic parameters
--> $DIR/undeclared-generic-parameter.rs:1:8
|
LL | struct A;
| ^

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0107, E0425.
For more information about an error, try `rustc --explain E0107`.
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