Mark GAT WC as GoalSource::AliasWellFormed so that we recurse into them in error reporting

compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs

@@ -134,7 +134,7 @@ where
                     // Add GAT where clauses from the trait's definition
                     // FIXME: We don't need these, since these are the type's own WF obligations.
                     ecx.add_goals(
-                        GoalSource::Misc,
+                        GoalSource::AliasWellFormed,
                         cx.own_predicates_of(goal.predicate.def_id())
                             .iter_instantiated(cx, goal.predicate.alias.args)
                             .map(|pred| goal.with(cx, pred)),
@@ -199,7 +199,7 @@ where
             // Add GAT where clauses from the trait's definition.
             // FIXME: We don't need these, since these are the type's own WF obligations.
             ecx.add_goals(
-                GoalSource::Misc,
+                GoalSource::AliasWellFormed,
                 cx.own_predicates_of(goal.predicate.def_id())
                     .iter_instantiated(cx, goal.predicate.alias.args)
                     .map(|pred| goal.with(cx, pred)),

compiler/rustc_type_ir/src/solve/mod.rs

@@ -83,8 +83,11 @@ pub enum GoalSource {
     /// Instantiating a higher-ranked goal and re-proving it.
     InstantiateHigherRanked,
     /// Predicate required for an alias projection to be well-formed.
-    /// This is used in two places: projecting to an opaque whose hidden type
+    /// This is used in three places:
-    /// is already registered in the opaque type storage, and for rigid projections.
+    /// 1. projecting to an opaque whose hidden type is already registered in
+    ///    the opaque type storage,
+    /// 2. for rigid projections's trait goal,
+    /// 3. for GAT where clauses.
     AliasWellFormed,
     /// In case normalizing aliases in nested goals cycles, eagerly normalizing these
     /// aliases in the context of the parent may incorrectly change the cycle kind.

tests/ui/traits/trivial-unsized-projection.bad_new.stderr

@@ -1,11 +1,3 @@
-error[E0271]: type mismatch resolving `<[()] as Bad>::Assert normalizes-to <[()] as Bad>::Assert`
-  --> $DIR/trivial-unsized-projection.rs:20:12
-   |
-LL | const FOO: <[()] as Bad>::Assert = todo!();
-   |            ^^^^^^^^^^^^^^^^^^^^^ types differ
-   |
-   = note: statics and constants must have a statically known size
-
 error[E0277]: the size for values of type `[()]` cannot be known at compilation time
   --> $DIR/trivial-unsized-projection.rs:20:12
    |
@@ -47,15 +39,6 @@ help: consider relaxing the implicit `Sized` restriction
 LL |     type Assert: ?Sized
    |                ++++++++
 
-error[E0271]: type mismatch resolving `<[()] as Bad>::Assert normalizes-to <[()] as Bad>::Assert`
+error: aborting due to 2 previous errors
-  --> $DIR/trivial-unsized-projection.rs:20:36
-   |
-LL | const FOO: <[()] as Bad>::Assert = todo!();
-   |                                    ^^^^^^^ types differ
-   |
-   = note: this error originates in the macro `todo` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 4 previous errors
+For more information about this error, try `rustc --explain E0277`.
-
-Some errors have detailed explanations: E0271, E0277.
-For more information about an error, try `rustc --explain E0271`.

tests/ui/traits/trivial-unsized-projection.rs

@@ -22,8 +22,6 @@ const FOO: <[()] as Bad>::Assert = todo!();
 //[bad]~| ERROR the size for values of type `[()]` cannot be known at compilation time
 //[bad_new]~^^^ ERROR the size for values of type `[()]` cannot be known at compilation time
 //[bad_new]~| ERROR the size for values of type `[()]` cannot be known at compilation time
-//[bad_new]~| ERROR type mismatch resolving `<[()] as Bad>::Assert normalizes-to <[()] as Bad>::Assert`
-//[bad_new]~| ERROR type mismatch resolving `<[()] as Bad>::Assert normalizes-to <[()] as Bad>::Assert`
 
 #[cfg(any(good, good_new))]
 // Well-formed in trivially false param-env