w

Author: lcnr

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -964,6 +964,9 @@ impl<'a, 'tcx> ProofTreeVisitor<'tcx> for AmbiguityCausesVisitor<'a> {
                 let lazily_normalize_ty = |ty: Ty<'tcx>| {
                     let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(infcx);
                     if matches!(ty.kind(), ty::Alias(..)) {
+                        // FIXME(-Ztrait-solver=next-coherence): we currently don't
+                        // normalize opaque types here, resulting in diverging behavior
+                        // for TAITs.
                         match infcx
                             .at(&ObligationCause::dummy(), param_env)
                             .structurally_normalize(ty, &mut *fulfill_cx)

tests/ui/coherence/inter-crate-ambiguity-causes-notes.next.stderr

@@ -7,7 +7,7 @@ LL | impl From<()> for S {
 LL | impl<I> From<I> for S
    | ^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `S`
    |
-   = note: downstream crates may implement trait `std::iter::Iterator` for type `()`
+   = note: upstream crates may add a new impl of trait `std::iter::Iterator` for type `()` in future versions
 
 error: aborting due to previous error
 

tests/ui/impl-trait/coherence-treats-tait-ambig.next.stderr

@@ -1,3 +1,7 @@
+WARN rustc_trait_selection::traits::coherence expected an unknowable trait ref: <T as std::convert::From<Foo>>
+WARN rustc_trait_selection::traits::coherence expected an unknowable trait ref: <T as std::convert::From<Foo>>
+WARN rustc_trait_selection::traits::coherence expected an unknowable trait ref: <T as std::convert::From<Foo>>
+WARN rustc_trait_selection::traits::coherence expected an unknowable trait ref: <T as std::convert::From<Foo>>
 error[E0119]: conflicting implementations of trait `Into<T>` for type `Foo`
   --> $DIR/coherence-treats-tait-ambig.rs:10:1
    |
@@ -7,7 +11,6 @@ LL | impl Into<T> for Foo {
    = note: conflicting implementation in crate `core`:
            - impl<T, U> Into<U> for T
              where U: From<T>;
-   = note: downstream crates may implement trait `std::convert::From<Foo>` for type `T`
 
 error: aborting due to previous error
 

tests/ui/impl-trait/coherence-treats-tait-ambig.rs

@@ -1,6 +1,3 @@
-// revisions: current next
-//[next] compile-flags: -Ztrait-solver=next
-
 #![feature(type_alias_impl_trait)]
 
 type T = impl Sized;

tests/ui/impl-trait/coherence-treats-tait-ambig.stderr

@@ -0,0 +1,13 @@
+error[E0119]: conflicting implementations of trait `Into<T>` for type `Foo`
+  --> $DIR/coherence-treats-tait-ambig.rs:7:1
+   |
+LL | impl Into<T> for Foo {
+   | ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: conflicting implementation in crate `core`:
+           - impl<T, U> Into<U> for T
+             where U: From<T>;
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0119`.