Rollup merge of #118210 - lcnr:intercrate-ambiguity-causes-uwu, r=compiler-errors

intercrate ambiguity causes: ignore candidates which don't apply

r? `@compiler-errors`

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -1050,8 +1050,10 @@ fn visit_goal(&mut self, goal: &InspectGoal<'_, 'tcx>) -> ControlFlow<Self::Brea
         let mut ambiguity_cause = None;
         for cand in goal.candidates() {
             // FIXME: boiiii, using string comparisions here sure is scuffed.
-            if let inspect::ProbeKind::MiscCandidate { name: "coherence unknowable", result: _ } =
+            if let inspect::ProbeKind::MiscCandidate {
-                cand.kind()
+                name: "coherence unknowable",
+                result: Ok(_),
+            } = cand.kind()
             {
                 let lazily_normalize_ty = |ty: Ty<'tcx>| {
                     let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(infcx);

tests/ui/error-codes/E0476.next.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `CoerceUnsized<&Wrapper<_>>` for type `&Wrapper<_>`
-  --> $DIR/E0476.rs:9:1
+  --> $DIR/E0476.rs:11:1
    |
 LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -9,18 +9,18 @@ LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S
              where 'b: 'a, T: Unsize<U>, T: ?Sized, U: ?Sized;
 
 error[E0476]: lifetime of the source pointer does not outlive lifetime bound of the object type
-  --> $DIR/E0476.rs:9:1
+  --> $DIR/E0476.rs:11:1
    |
 LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: object type is valid for the lifetime `'a` as defined here
-  --> $DIR/E0476.rs:9:6
+  --> $DIR/E0476.rs:11:6
    |
 LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
    |      ^^
 note: source pointer is only valid for the lifetime `'b` as defined here
-  --> $DIR/E0476.rs:9:10
+  --> $DIR/E0476.rs:11:10
    |
 LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
    |          ^^

tests/ui/error-codes/E0476.old.stderr

@@ -0,0 +1,31 @@
+error[E0119]: conflicting implementations of trait `CoerceUnsized<&Wrapper<_>>` for type `&Wrapper<_>`
+  --> $DIR/E0476.rs:11:1
+   |
+LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: conflicting implementation in crate `core`:
+           - impl<'a, 'b, T, U> CoerceUnsized<&'a U> for &'b T
+             where 'b: 'a, T: Unsize<U>, T: ?Sized, U: ?Sized;
+
+error[E0476]: lifetime of the source pointer does not outlive lifetime bound of the object type
+  --> $DIR/E0476.rs:11:1
+   |
+LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: object type is valid for the lifetime `'a` as defined here
+  --> $DIR/E0476.rs:11:6
+   |
+LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
+   |      ^^
+note: source pointer is only valid for the lifetime `'b` as defined here
+  --> $DIR/E0476.rs:11:10
+   |
+LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
+   |          ^^
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0119, E0476.
+For more information about an error, try `rustc --explain E0119`.

tests/ui/error-codes/E0476.rs

@@ -1,3 +1,5 @@
+// revisions: old next
+//[next] compile-flags: -Ztrait-solver=next-coherence
 #![feature(coerce_unsized)]
 #![feature(unsize)]