Walk into alias-eq nested goals even if normalization fails

compiler/rustc_trait_selection/src/solve/alias_relate.rs

@@ -48,6 +48,12 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
             rhs
         };
 
+        // Add a `make_canonical_response` probe step so that we treat this as
+        // a candidate, even if `try_evaluate_added_goals` bails due to an error.
+        // It's `Certainty::AMBIGUOUS` because this candidate is not "finished",
+        // since equating the normalized terms will lead to additional constraints.
+        self.inspect.make_canonical_response(Certainty::AMBIGUOUS);
+
         // Apply the constraints.
         self.try_evaluate_added_goals()?;
         let lhs = self.resolve_vars_if_possible(lhs);

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -460,9 +460,8 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
                     polarity: ty::PredicatePolarity::Positive,
                 }))
             }
-            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(_)) => {
+            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(_))
-                ChildMode::WellFormedObligation
+            | ty::PredicateKind::AliasRelate(..) => ChildMode::PassThrough,
-            }
             _ => {
                 return ControlFlow::Break(self.obligation.clone());
             }
@@ -496,7 +495,7 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
                 (_, GoalSource::InstantiateHigherRanked) => {
                     obligation = self.obligation.clone();
                 }
-                (ChildMode::WellFormedObligation, _) => {
+                (ChildMode::PassThrough, _) => {
                     obligation = make_obligation(self.obligation.cause.clone());
                 }
             }
@@ -527,7 +526,7 @@ enum ChildMode<'tcx> {
     // Skip trying to derive an `ObligationCause` from this obligation, and
     // report *all* sub-obligations as if they came directly from the parent
     // obligation.
-    WellFormedObligation,
+    PassThrough,
 }
 
 fn derive_cause<'tcx>(

compiler/rustc_trait_selection/src/solve/inspect/analyse.rs

@@ -15,7 +15,7 @@ use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk};
 use rustc_macros::extension;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{inspect, QueryResult};
-use rustc_middle::traits::solve::{Certainty, Goal};
+use rustc_middle::traits::solve::{Certainty, Goal, MaybeCause};
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::{TyCtxt, TypeFoldable};
 use rustc_middle::{bug, ty};
@@ -291,7 +291,10 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
                     steps.push(step)
                 }
                 inspect::ProbeStep::MakeCanonicalResponse { shallow_certainty: c } => {
-                    assert_eq!(shallow_certainty.replace(c), None);
+                    assert!(matches!(
+                        shallow_certainty.replace(c),
+                        None | Some(Certainty::Maybe(MaybeCause::Ambiguity))
+                    ));
                 }
                 inspect::ProbeStep::NestedProbe(ref probe) => {
                     match probe.kind {

tests/ui/coherence/indirect-impl-for-trait-obj-coherence.next.stderr

@@ -1,8 +1,8 @@
-error[E0284]: type annotations needed: cannot satisfy `<dyn Object<U, Output = T> as Object<U>>::Output == T`
+error[E0284]: type annotations needed: cannot satisfy `<dyn Object<U, Output = T> as Object<U>>::Output normalizes-to _`
   --> $DIR/indirect-impl-for-trait-obj-coherence.rs:25:41
    |
 LL |     foo::<dyn Object<U, Output = T>, U>(x)
-   |                                         ^ cannot satisfy `<dyn Object<U, Output = T> as Object<U>>::Output == T`
+   |                                         ^ cannot satisfy `<dyn Object<U, Output = T> as Object<U>>::Output normalizes-to _`
 
 error: aborting due to 1 previous error
 

tests/ui/coherence/indirect-impl-for-trait-obj-coherence.rs

@@ -23,7 +23,7 @@ fn foo<T: ?Sized, U>(x: <T as Object<U>>::Output) -> U {
 #[allow(dead_code)]
 fn transmute<T, U>(x: T) -> U {
     foo::<dyn Object<U, Output = T>, U>(x)
-    //[next]~^ ERROR type annotations needed: cannot satisfy `<dyn Object<U, Output = T> as Object<U>>::Output == T`
+    //[next]~^ ERROR type annotations needed: cannot satisfy `<dyn Object<U, Output = T> as Object<U>>::Output normalizes-to _`
 }
 
 fn main() {}

tests/ui/coherence/occurs-check/associated-type.next.stderr

@@ -16,11 +16,11 @@ LL | |     for<'a> *const T: ToUnit<'a>,
    |
    = note: this behavior recently changed as a result of a bug fix; see rust-lang/rust#56105 for details
 
-error[E0284]: type annotations needed: cannot satisfy `<for<'a> fn(&'a (), ()) as Overlap<for<'a> fn(&'a (), ())>>::Assoc == usize`
+error[E0284]: type annotations needed: cannot satisfy `<for<'a> fn(&'a (), ()) as Overlap<for<'a> fn(&'a (), ())>>::Assoc normalizes-to _`
   --> $DIR/associated-type.rs:44:59
    |
 LL |     foo::<for<'a> fn(&'a (), ()), for<'a> fn(&'a (), ())>(3usize);
-   |                                                           ^^^^^^ cannot satisfy `<for<'a> fn(&'a (), ()) as Overlap<for<'a> fn(&'a (), ())>>::Assoc == usize`
+   |                                                           ^^^^^^ cannot satisfy `<for<'a> fn(&'a (), ()) as Overlap<for<'a> fn(&'a (), ())>>::Assoc normalizes-to _`
 
 error: aborting due to 2 previous errors
 

tests/ui/diagnostic_namespace/do_not_recommend/as_expression.next.stderr

@@ -25,7 +25,7 @@ LL |     SelectInt.check("bar");
    = help: the trait `AsExpression<Text>` is implemented for `&str`
    = help: for that trait implementation, expected `Text`, found `Integer`
 
-error[E0271]: type mismatch resolving `<&str as AsExpression<<SelectInt as Expression>::SqlType>>::Expression == _`
+error[E0271]: type mismatch resolving `<SelectInt as Expression>::SqlType == Text`
   --> $DIR/as_expression.rs:57:5
    |
 LL |     SelectInt.check("bar");

tests/ui/traits/negative-bounds/opaque-type-unsatisfied-bound.rs

@@ -18,3 +18,4 @@ fn weird1() -> impl !Sized + Sized {}
 //~^ ERROR type mismatch resolving `impl !Sized + Sized == ()`
 fn weird2() -> impl !Sized {}
 //~^ ERROR type mismatch resolving `impl !Sized == ()`
+//~| ERROR the size for values of type `impl !Sized` cannot be known at compilation time

tests/ui/traits/negative-bounds/opaque-type-unsatisfied-bound.stderr

@@ -16,6 +16,15 @@ error[E0271]: type mismatch resolving `impl !Sized == ()`
 LL | fn weird2() -> impl !Sized {}
    |                ^^^^^^^^^^^ types differ
 
+error[E0277]: the size for values of type `impl !Sized` cannot be known at compilation time
+  --> $DIR/opaque-type-unsatisfied-bound.rs:19:16
+   |
+LL | fn weird2() -> impl !Sized {}
+   |                ^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `impl !Sized`
+   = note: the return type of a function must have a statically known size
+
 error[E0277]: the trait bound `impl !Trait: Trait` is not satisfied
   --> $DIR/opaque-type-unsatisfied-bound.rs:12:13
    |
@@ -30,7 +39,7 @@ note: required by a bound in `consume`
 LL | fn consume(_: impl Trait) {}
    |                    ^^^^^ required by this bound in `consume`
 
-error: aborting due to 4 previous errors
+error: aborting due to 5 previous errors
 
 Some errors have detailed explanations: E0271, E0277.
 For more information about an error, try `rustc --explain E0271`.

tests/ui/traits/next-solver/canonical/const-region-infer-to-static-in-binder.stderr

@@ -1,8 +1,8 @@
-error[E0284]: type annotations needed: cannot satisfy `{ || {} } == _`
+error[E0284]: type annotations needed: cannot satisfy `X::{constant#0} normalizes-to _`
   --> $DIR/const-region-infer-to-static-in-binder.rs:4:10
    |
 LL | struct X<const FN: fn() = { || {} }>;
-   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot satisfy `{ || {} } == _`
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot satisfy `X::{constant#0} normalizes-to _`
 
 error: using function pointers as const generic parameters is forbidden
   --> $DIR/const-region-infer-to-static-in-binder.rs:4:20

tests/ui/traits/next-solver/diagnostics/projection-trait-ref.rs

@@ -0,0 +1,17 @@
+//@ compile-flags: -Znext-solver
+
+trait Trait {
+    type Assoc;
+}
+
+fn test_poly<T>() {
+    let x: <T as Trait>::Assoc = ();
+    //~^ ERROR the trait bound `T: Trait` is not satisfied
+}
+
+fn test() {
+    let x: <i32 as Trait>::Assoc = ();
+    //~^ ERROR the trait bound `i32: Trait` is not satisfied
+}
+
+fn main() {}

tests/ui/traits/next-solver/diagnostics/projection-trait-ref.stderr

@@ -0,0 +1,26 @@
+error[E0277]: the trait bound `T: Trait` is not satisfied
+  --> $DIR/projection-trait-ref.rs:8:12
+   |
+LL |     let x: <T as Trait>::Assoc = ();
+   |            ^^^^^^^^^^^^^^^^^^^ the trait `Trait` is not implemented for `T`
+   |
+help: consider restricting type parameter `T`
+   |
+LL | fn test_poly<T: Trait>() {
+   |               +++++++
+
+error[E0277]: the trait bound `i32: Trait` is not satisfied
+  --> $DIR/projection-trait-ref.rs:13:12
+   |
+LL |     let x: <i32 as Trait>::Assoc = ();
+   |            ^^^^^^^^^^^^^^^^^^^^^ the trait `Trait` is not implemented for `i32`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/projection-trait-ref.rs:3:1
+   |
+LL | trait Trait {
+   | ^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

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

@@ -10,17 +10,17 @@ LL | #![feature(specialization)]
 
 error: cannot normalize `<T as Default>::Id: '_`
 
-error[E0284]: type annotations needed: cannot satisfy `<T as Default>::Id == _`
+error[E0284]: type annotations needed: cannot satisfy `<T as Default>::Id normalizes-to _`
   --> $DIR/specialization-transmute.rs:15:23
    |
 LL |     fn intu(&self) -> &Self::Id {
-   |                       ^^^^^^^^^ cannot satisfy `<T as Default>::Id == _`
+   |                       ^^^^^^^^^ cannot satisfy `<T as Default>::Id normalizes-to _`
 
-error[E0284]: type annotations needed: cannot satisfy `T <: <T as Default>::Id`
+error[E0284]: type annotations needed: cannot satisfy `<T as Default>::Id normalizes-to T`
   --> $DIR/specialization-transmute.rs:17:9
    |
 LL |         self
-   |         ^^^^ cannot satisfy `T <: <T as Default>::Id`
+   |         ^^^^ cannot satisfy `<T as Default>::Id normalizes-to T`
 
 error[E0284]: type annotations needed: cannot satisfy `<u8 as Default>::Id == Option<NonZero<u8>>`
   --> $DIR/specialization-transmute.rs:28:13

tests/ui/type-alias-impl-trait/issue-84660-unsoundness.next.stderr

@@ -1,4 +1,4 @@
-error[E0284]: type annotations needed: cannot satisfy `<Out as Trait<Bar, In>>::Out == ()`
+error[E0284]: type annotations needed: cannot satisfy `Bar == _`
   --> $DIR/issue-84660-unsoundness.rs:22:37
    |
 LL |       fn convert(_i: In) -> Self::Out {
@@ -7,7 +7,7 @@ LL | |
 LL | |
 LL | |         unreachable!();
 LL | |     }
-   | |_____^ cannot satisfy `<Out as Trait<Bar, In>>::Out == ()`
+   | |_____^ cannot satisfy `Bar == _`
 
 error[E0119]: conflicting implementations of trait `Trait<Bar, _>`
   --> $DIR/issue-84660-unsoundness.rs:29:1