Fix regression introduced with #99383

compiler/rustc_traits/src/evaluate_obligation.rs

@@ -1,4 +1,4 @@
-use rustc_infer::infer::TyCtxtInferExt;
+use rustc_infer::infer::{DefiningAnchor, TyCtxtInferExt};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{ParamEnvAnd, TyCtxt};
 use rustc_span::source_map::DUMMY_SP;
@@ -16,7 +16,9 @@ fn evaluate_obligation<'tcx>(
     canonical_goal: CanonicalPredicateGoal<'tcx>,
 ) -> Result<EvaluationResult, OverflowError> {
     debug!("evaluate_obligation(canonical_goal={:#?})", canonical_goal);
-    tcx.infer_ctxt().enter_with_canonical(
+    // HACK This bubble is required for this tests to pass:
+    // impl-trait/issue99642.rs
+    tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).enter_with_canonical(
         DUMMY_SP,
         &canonical_goal,
         |ref infcx, goal, _canonical_inference_vars| {

compiler/rustc_traits/src/type_op.rs

@@ -2,7 +2,7 @@ use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
-use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
+use rustc_infer::infer::{DefiningAnchor, InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::TraitEngineExt as _;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::subst::{GenericArg, Subst, UserSelfTy, UserSubsts};
@@ -258,10 +258,15 @@ fn type_op_prove_predicate<'tcx>(
     tcx: TyCtxt<'tcx>,
     canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, ProvePredicate<'tcx>>>,
 ) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, ()>>, NoSolution> {
-    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |infcx, fulfill_cx, key| {
-        type_op_prove_predicate_with_cause(infcx, fulfill_cx, key, ObligationCause::dummy());
-        Ok(())
-    })
+    // HACK This bubble is required for this test to pass:
+    // impl-trait/issue-99642.rs
+    tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).enter_canonical_trait_query(
+        &canonicalized,
+        |infcx, fulfill_cx, key| {
+            type_op_prove_predicate_with_cause(infcx, fulfill_cx, key, ObligationCause::dummy());
+            Ok(())
+        },
+    )
 }
 
 /// The core of the `type_op_prove_predicate` query: for diagnostics purposes in NLL HRTB errors,

src/test/ui/impl-trait/issue-99642-2.rs

@@ -0,0 +1,8 @@
+// check-pass
+
+#![feature(type_alias_impl_trait)]
+type Opq = impl Sized;
+fn test() -> impl Iterator<Item = Opq> {
+    Box::new(0..) as Box<dyn Iterator<Item = _>>
+}
+fn main(){}

src/test/ui/impl-trait/issue-99642.rs

@@ -0,0 +1,7 @@
+// check-pass
+
+fn test() -> impl Iterator<Item = impl Sized> {
+    Box::new(0..) as Box<dyn Iterator<Item = _>>
+}
+
+fn main() {}

src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.stderr

@@ -1,8 +1,10 @@
-error[E0275]: overflow evaluating the requirement `<fn() -> Foo {foo} as FnOnce<()>>::Output == fn() -> Foo {foo}`
+error[E0275]: overflow evaluating the requirement `fn() -> Foo {foo}: Sized`
   --> $DIR/issue-53398-cyclic-types.rs:5:13
    |
 LL | fn foo() -> Foo {
    |             ^^^
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_53398_cyclic_types`)
 
 error: aborting due to previous error