Skip expected_projection if proj_ty is forbidden

Author: mu001999

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -609,6 +609,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
                 terr,
                 false,
                 false,
+                false,
             );
             return Err(diag.emit());
         }
@@ -1031,6 +1032,7 @@ fn report_trait_method_mismatch<'tcx>(
         terr,
         false,
         false,
+        false,
     );
 
     return diag.emit();
@@ -1838,6 +1840,7 @@ fn compare_const_predicate_entailment<'tcx>(
             terr,
             false,
             false,
+            false,
         );
         return Err(diag.emit());
     };

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -626,6 +626,7 @@ pub fn check_function_signature<'tcx>(
                 err,
                 false,
                 false,
+                false,
             );
             return Err(diag.emit());
         }

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -1032,6 +1032,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 e,
                                 false,
                                 true,
+                                false,
                             );
                         }
                     }

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1523,6 +1523,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         terr: TypeError<'tcx>,
         swap_secondary_and_primary: bool,
         prefer_label: bool,
+        const_arg_has_assoc_type: bool,
     ) {
         let span = cause.span();
 
@@ -1982,12 +1983,26 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
         self.check_and_note_conflicting_crates(diag, terr);
 
-        self.note_and_explain_type_err(diag, terr, cause, span, cause.body_id.to_def_id());
+        self.note_and_explain_type_err(
+            diag,
+            terr,
+            cause,
+            span,
+            cause.body_id.to_def_id(),
+            const_arg_has_assoc_type,
+        );
         if let Some(exp_found) = exp_found
             && let exp_found = TypeError::Sorts(exp_found)
             && exp_found != terr
         {
-            self.note_and_explain_type_err(diag, exp_found, cause, span, cause.body_id.to_def_id());
+            self.note_and_explain_type_err(
+                diag,
+                exp_found,
+                cause,
+                span,
+                cause.body_id.to_def_id(),
+                false,
+            );
         }
 
         if let Some(ValuePairs::TraitRefs(exp_found)) = values
@@ -2169,7 +2184,16 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             self.type_error_additional_suggestions(&trace, terr),
         );
         let mut diag = self.tcx.dcx().create_err(failure_code);
-        self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr, false, false);
+        self.note_type_err(
+            &mut diag,
+            &trace.cause,
+            None,
+            Some(trace.values),
+            terr,
+            false,
+            false,
+            false,
+        );
         diag
     }
 

compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs

@@ -20,6 +20,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         cause: &ObligationCause<'tcx>,
         sp: Span,
         body_owner_def_id: DefId,
+        const_arg_has_assoc_type: bool,
     ) {
         use ty::error::TypeError::*;
         debug!("note_and_explain_type_err err={:?} cause={:?}", err, cause);
@@ -242,7 +243,8 @@ impl<T> Trait<T> for X {
                         }
                     }
                     (ty::Alias(ty::Projection | ty::Inherent, proj_ty), _)
-                        if !tcx.is_impl_trait_in_trait(proj_ty.def_id) =>
+                        if !tcx.is_impl_trait_in_trait(proj_ty.def_id)
+                            && !const_arg_has_assoc_type =>
                     {
                         self.expected_projection(
                             diag,

compiler/rustc_passes/src/check_attr.rs

@@ -2397,6 +2397,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 terr,
                 false,
                 false,
+                false,
             );
             diag.emit();
             self.abort.set(true);

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -932,6 +932,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             TypeError::Sorts(ty::error::ExpectedFound::new(true, ty, ct.ty())),
                             false,
                             false,
+                            // proj_ty is forbidden as the type of a const generic parameter
+                            matches!(ty.kind(), ty::Alias(ty::Projection | ty::Inherent, _)),
                         );
                         diag
                     }
@@ -1741,6 +1743,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 err,
                 true,
                 false,
+                false,
             );
             self.note_obligation_cause(&mut diag, obligation);
             diag.emit()

tests/ui/specialization/skip-expect-proj-if-forbidden-issue-125757.rs

@@ -0,0 +1,19 @@
+#![feature(specialization)]
+#![allow(incomplete_features)]
+
+trait Trait {
+    type Type;
+}
+
+impl Trait for i32 {
+    default type Type = i32;
+}
+
+struct Wrapper<const C: <i32 as Trait>::Type> {}
+//~^ ERROR `<i32 as Trait>::Type` is forbidden as the type of a const generic parameter
+
+impl<const C: usize> Wrapper<C> {}
+//~^ ERROR the constant `C` is not of type `<i32 as Trait>::Type`
+//~^^ ERROR mismatched types
+
+fn main() {}

tests/ui/specialization/skip-expect-proj-if-forbidden-issue-125757.stderr

@@ -0,0 +1,34 @@
+error: `<i32 as Trait>::Type` is forbidden as the type of a const generic parameter
+  --> $DIR/skip-expect-proj-if-forbidden-issue-125757.rs:12:25
+   |
+LL | struct Wrapper<const C: <i32 as Trait>::Type> {}
+   |                         ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: the only supported types are integers, `bool` and `char`
+
+error: the constant `C` is not of type `<i32 as Trait>::Type`
+  --> $DIR/skip-expect-proj-if-forbidden-issue-125757.rs:15:22
+   |
+LL | impl<const C: usize> Wrapper<C> {}
+   |                      ^^^^^^^^^^ expected associated type, found `usize`
+   |
+note: required by a bound in `Wrapper`
+  --> $DIR/skip-expect-proj-if-forbidden-issue-125757.rs:12:16
+   |
+LL | struct Wrapper<const C: <i32 as Trait>::Type> {}
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Wrapper`
+
+error[E0308]: mismatched types
+  --> $DIR/skip-expect-proj-if-forbidden-issue-125757.rs:15:30
+   |
+LL | impl<const C: usize> Wrapper<C> {}
+   |                              ^ expected associated type, found `usize`
+   |
+   = note: expected associated type `<i32 as Trait>::Type`
+                         found type `usize`
+   = help: consider constraining the associated type `<i32 as Trait>::Type` to `usize`
+   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0308`.