Dont bail in error predicate unless self ty is error

Author: compiler-errors

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

@@ -199,6 +199,7 @@ where
     /// but prevents incorrect normalization while hiding any trait errors.
     fn consider_error_guaranteed_candidate(
         ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
         guar: I::ErrorGuaranteed,
     ) -> Result<Candidate<I>, NoSolution>;
 
@@ -539,8 +540,8 @@ where
         // Instead of adding the logic here, it's a better idea to add it in
         // `EvalCtxt::disqualify_auto_trait_candidate_due_to_possible_impl` in
         // `solve::trait_goals` instead.
-        let result = if let Err(guar) = goal.predicate.error_reported() {
-            G::consider_error_guaranteed_candidate(self, guar)
+        let result = if let ty::Error(guar) = goal.predicate.self_ty().kind() {
+            G::consider_error_guaranteed_candidate(self, goal, guar)
         } else if cx.trait_is_auto(trait_def_id) {
             G::consider_auto_trait_candidate(self, goal)
         } else if cx.trait_is_alias(trait_def_id) {

compiler/rustc_next_trait_solver/src/solve/effect_goals.rs

@@ -182,6 +182,7 @@ where
 
     fn consider_error_guaranteed_candidate(
         ecx: &mut EvalCtxt<'_, D>,
+        _goal: Goal<I, Self>,
         _guar: I::ErrorGuaranteed,
     ) -> Result<Candidate<I>, NoSolution> {
         ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc)

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

@@ -396,10 +396,21 @@ where
     /// Fail to normalize if the predicate contains an error, alternatively, we could normalize to `ty::Error`
     /// and succeed. Can experiment with this to figure out what results in better error messages.
     fn consider_error_guaranteed_candidate(
-        _ecx: &mut EvalCtxt<'_, D>,
-        _guar: I::ErrorGuaranteed,
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+        guar: I::ErrorGuaranteed,
     ) -> Result<Candidate<I>, NoSolution> {
-        Err(NoSolution)
+        let cx = ecx.cx();
+        let error_term = match goal.predicate.alias.kind(cx) {
+            ty::AliasTermKind::ProjectionTy => Ty::new_error(cx, guar).into(),
+            ty::AliasTermKind::ProjectionConst => Const::new_error(cx, guar).into(),
+            kind => panic!("expected projection, found {kind:?}"),
+        };
+
+        ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc).enter(|ecx| {
+            ecx.instantiate_normalizes_to_term(goal, error_term);
+            ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+        })
     }
 
     fn consider_auto_trait_candidate(

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

@@ -121,6 +121,7 @@ where
 
     fn consider_error_guaranteed_candidate(
         ecx: &mut EvalCtxt<'_, D>,
+        _goal: Goal<I, Self>,
         _guar: I::ErrorGuaranteed,
     ) -> Result<Candidate<I>, NoSolution> {
         ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc)

compiler/rustc_type_ir/src/ty_kind/closure.rs

@@ -462,6 +462,15 @@ impl<I: Interner> CoroutineClosureSignature<I> {
         coroutine_captures_by_ref_ty: I::Ty,
         env_region: I::Region,
     ) -> I::Ty {
+        // If either of the tupled capture types are constrained to error
+        // (e.g. during typeck when the infcx is tainted), then just return
+        // the error type directly.
+        if let ty::Error(_) = tupled_inputs_ty.kind() {
+            return tupled_inputs_ty;
+        } else if let ty::Error(_) = coroutine_captures_by_ref_ty.kind() {
+            return coroutine_captures_by_ref_ty;
+        }
+
         match kind {
             ty::ClosureKind::Fn | ty::ClosureKind::FnMut => {
                 let ty::FnPtr(sig_tys, _) = coroutine_captures_by_ref_ty.kind() else {