Don't cancel stashed TraitMissingMethod errors.

This gives one extra error message on two tests, but is necessary to fix
bigger problems caused by the cancellation of stashed errors.

(Note: why not just avoid stashing altogether? Because that resulted in
additional output changes.)

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -879,17 +879,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  );
  }
 
- // emit or cancel the diagnostic for bare traits
+ // Emit the diagnostic for bare traits. (We used to cancel for slightly better
+ // error messages, but cancelling stashed diagnostics is no longer allowed because
+ // it causes problems when tracking whether errors have actually occurred.)
  if span.edition().at_least_rust_2021()
  && let Some(diag) =
  self.dcx().steal_diagnostic(qself.span, StashKey::TraitMissingMethod)
  {
- if trait_missing_method {
- // cancel the diag for bare traits when meeting `MyTrait::missing_method`
- diag.cancel();
- } else {
- diag.emit();
- }
+ diag.emit();
  }
 
  if item_name.name != kw::Empty {

tests/ui/resolve/issue-111312.rs

@@ -7,5 +7,7 @@ trait Has {
 trait HasNot {}
 
 fn main() {
- HasNot::has(); //~ ERROR
+ HasNot::has();
+ //~^ ERROR trait objects must include the `dyn` keyword
+ //~| ERROR no function or associated item named `has` found for trait `HasNot`
 }

tests/ui/resolve/issue-111312.stderr

@@ -1,3 +1,14 @@
+error[E0782]: trait objects must include the `dyn` keyword
+ --> $DIR/issue-111312.rs:10:5
+ |
+LL | HasNot::has();
+ | ^^^^^^
+ |
+help: add `dyn` keyword before this trait
+ |
+LL | <dyn HasNot>::has();
+ | ++++ +
+
 error[E0599]: no function or associated item named `has` found for trait `HasNot`
  --> $DIR/issue-111312.rs:10:13
  |
@@ -10,6 +21,7 @@ note: `Has` defines an item `has`
 LL | trait Has {
  | ^^^^^^^^^
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0599`.
+Some errors have detailed explanations: E0599, E0782.
+For more information about an error, try `rustc --explain E0599`.

tests/ui/resolve/issue-111727.rs

@@ -1,5 +1,7 @@
 //@ edition: 2021
 
 fn main() {
- std::any::Any::create(); //~ ERROR
+ std::any::Any::create();
+ //~^ ERROR trait objects must include the `dyn` keyword
+ //~| ERROR no function or associated item named `create` found for trait `Any`
 }

tests/ui/resolve/issue-111727.stderr

@@ -1,9 +1,21 @@
+error[E0782]: trait objects must include the `dyn` keyword
+ --> $DIR/issue-111727.rs:4:5
+ |
+LL | std::any::Any::create();
+ | ^^^^^^^^^^^^^
+ |
+help: add `dyn` keyword before this trait
+ |
+LL | <dyn std::any::Any>::create();
+ | ++++ +
+
 error[E0599]: no function or associated item named `create` found for trait `Any`
  --> $DIR/issue-111727.rs:4:20
  |
 LL | std::any::Any::create();
  | ^^^^^^ function or associated item not found in `Any`
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0599`.
+Some errors have detailed explanations: E0599, E0782.
+For more information about an error, try `rustc --explain E0599`.