Re-use error code for duplicate error

Author: oli-obk

compiler/rustc_ty_utils/src/errors.rs

@@ -113,7 +113,7 @@ pub struct DuplicateArg<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(ty_utils_impl_trait_not_param)]
+#[diag(ty_utils_impl_trait_not_param, code = "E0792")]
 pub struct NotParam<'tcx> {
     pub arg: GenericArg<'tcx>,
     #[primary_span]

tests/ui/type-alias-impl-trait/multi-error.stderr

@@ -1,4 +1,4 @@
-error: non-defining opaque type use in defining scope
+error[E0792]: non-defining opaque type use in defining scope
   --> $DIR/multi-error.rs:17:17
    |
 LL |     fn foo() -> (Self::Bar<u32>, Self::Baz) {
@@ -12,3 +12,4 @@ LL |     type Bar<T> = impl Sized;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0792`.

tests/ui/type-alias-impl-trait/non-defining-method.stderr

@@ -1,4 +1,4 @@
-error: non-defining opaque type use in defining scope
+error[E0792]: non-defining opaque type use in defining scope
   --> $DIR/non-defining-method.rs:16:17
    |
 LL |     fn foo() -> Self::Bar<u32> {}
@@ -12,3 +12,4 @@ LL |     type Bar<T> = impl Sized;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0792`.