Taint _ placeholder types

Author: oli-obk

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -2543,7 +2543,11 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
  self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, Some(i))
  {
  infer_replacements.push((a.span, suggested_ty.to_string()));
- return suggested_ty;
+ return Ty::new_error_with_message(
+ self.tcx(),
+ a.span,
+ suggested_ty.to_string(),
+ );
  }
  }
 
@@ -2561,7 +2565,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
  self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, None)
  {
  infer_replacements.push((output.span, suggested_ty.to_string()));
- suggested_ty
+ Ty::new_error_with_message(self.tcx(), output.span, suggested_ty.to_string())
  } else {
  visitor.visit_ty(output);
  self.ast_ty_to_ty(output)

tests/ui/traits/method-argument-mismatch-variance-ice-119867.rs

@@ -0,0 +1,13 @@
+trait Deserialize {
+ fn deserialize(&self);
+}
+
+struct ArchivedVec<T>(T);
+
+impl<T> Deserialize for ArchivedVec<T> {
+ fn deserialize(s: _) {}
+ //~^ ERROR: `_` is not allowed within types on item signatures
+ //~| ERROR: has a `&self` declaration in the trait, but not in the impl
+}
+
+fn main() {}

tests/ui/traits/method-argument-mismatch-variance-ice-119867.stderr

@@ -0,0 +1,24 @@
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for functions
+ --> $DIR/method-argument-mismatch-variance-ice-119867.rs:8:23
+ |
+LL | fn deserialize(s: _) {}
+ | ^ not allowed in type signatures
+ |
+help: try replacing `_` with the type in the corresponding trait method signature
+ |
+LL | fn deserialize(s: &ArchivedVec<T>) {}
+ | ~~~~~~~~~~~~~~~
+
+error[E0186]: method `deserialize` has a `&self` declaration in the trait, but not in the impl
+ --> $DIR/method-argument-mismatch-variance-ice-119867.rs:8:5
+ |
+LL | fn deserialize(&self);
+ | ---------------------- `&self` used in trait
+...
+LL | fn deserialize(s: _) {}
+ | ^^^^^^^^^^^^^^^^^^^^ expected `&self` in impl
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0121, E0186.
+For more information about an error, try `rustc --explain E0121`.