Also passthrough for projection clauses

Author: compiler-errors

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -460,7 +460,9 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
                     polarity: ty::PredicatePolarity::Positive,
                 }))
             }
-            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(_))
+            ty::PredicateKind::Clause(
+                ty::ClauseKind::WellFormed(_) | ty::ClauseKind::Projection(..),
+            )
             | ty::PredicateKind::AliasRelate(..) => ChildMode::PassThrough,
             _ => {
                 return ControlFlow::Break(self.obligation.clone());

tests/ui/traits/next-solver/env-shadows-impls/param-candidate-shadows-project.stderr

@@ -2,13 +2,8 @@ error[E0271]: type mismatch resolving `<T as Foo>::Assoc == i32`
   --> $DIR/param-candidate-shadows-project.rs:27:19
    |
 LL |     require_bar::<T>();
-   |                   ^ type mismatch resolving `<T as Foo>::Assoc == i32`
+   |                   ^ types differ
    |
-note: types differ
-  --> $DIR/param-candidate-shadows-project.rs:10:18
-   |
-LL |     type Assoc = i32;
-   |                  ^^^
 note: required for `T` to implement `Bar`
   --> $DIR/param-candidate-shadows-project.rs:13:9
    |

tests/ui/traits/next-solver/normalize/two-projection-param-candidates-are-ambiguous.rs

@@ -24,7 +24,7 @@ fn needs_bar<T: Bar>() {}
 
 fn foo<T: Foo<Assoc = i32> + Foo<Assoc = u32>>() {
     needs_bar::<T>();
-    //~^ ERROR type annotations needed: cannot satisfy `<T as Foo>::Assoc == i32`
+    //~^ ERROR type annotations needed: cannot normalize
 }
 
 fn main() {}

tests/ui/traits/next-solver/normalize/two-projection-param-candidates-are-ambiguous.stderr

@@ -1,8 +1,8 @@
-error[E0284]: type annotations needed: cannot satisfy `<T as Foo>::Assoc == i32`
+error[E0284]: type annotations needed: cannot normalize `<T as Foo>::Assoc`
   --> $DIR/two-projection-param-candidates-are-ambiguous.rs:26:17
    |
 LL |     needs_bar::<T>();
-   |                 ^ cannot satisfy `<T as Foo>::Assoc == i32`
+   |                 ^ cannot normalize `<T as Foo>::Assoc`
    |
 note: required for `T` to implement `Bar`
   --> $DIR/two-projection-param-candidates-are-ambiguous.rs:21:9

tests/ui/traits/next-solver/specialization-transmute.stderr

@@ -22,11 +22,11 @@ error[E0284]: type annotations needed: cannot satisfy `<T as Default>::Id normal
 LL |         self
    |         ^^^^ cannot satisfy `<T as Default>::Id normalizes-to T`
 
-error[E0284]: type annotations needed: cannot satisfy `<u8 as Default>::Id == Option<NonZero<u8>>`
+error[E0284]: type annotations needed: cannot satisfy `<u8 as Default>::Id normalizes-to Option<NonZero<u8>>`
   --> $DIR/specialization-transmute.rs:28:13
    |
 LL |     let s = transmute::<u8, Option<NonZero<u8>>>(0);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot satisfy `<u8 as Default>::Id == Option<NonZero<u8>>`
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot satisfy `<u8 as Default>::Id normalizes-to Option<NonZero<u8>>`
    |
 note: required by a bound in `transmute`
   --> $DIR/specialization-transmute.rs:21:25

tests/ui/traits/next-solver/specialization-unconstrained.rs

@@ -18,5 +18,5 @@ fn test<T: Default<Id = U>, U>() {}
 
 fn main() {
     test::<u32, ()>();
-    //~^ ERROR cannot satisfy `<u32 as Default>::Id == ()`
+    //~^ ERROR cannot satisfy `<u32 as Default>::Id normalizes-to ()`
 }

tests/ui/traits/next-solver/specialization-unconstrained.stderr

@@ -8,11 +8,11 @@ LL | #![feature(specialization)]
    = help: consider using `min_specialization` instead, which is more stable and complete
    = note: `#[warn(incomplete_features)]` on by default
 
-error[E0284]: type annotations needed: cannot satisfy `<u32 as Default>::Id == ()`
+error[E0284]: type annotations needed: cannot satisfy `<u32 as Default>::Id normalizes-to ()`
   --> $DIR/specialization-unconstrained.rs:20:5
    |
 LL |     test::<u32, ()>();
-   |     ^^^^^^^^^^^^^^^^^ cannot satisfy `<u32 as Default>::Id == ()`
+   |     ^^^^^^^^^^^^^^^^^ cannot satisfy `<u32 as Default>::Id normalizes-to ()`
    |
 note: required by a bound in `test`
   --> $DIR/specialization-unconstrained.rs:17:20