Properly drain pending obligations for coroutines

compiler/rustc_next_trait_solver/src/solve/mod.rs

@@ -329,7 +329,10 @@ where
             TypingMode::Coherence | TypingMode::PostAnalysis => false,
             // During analysis, opaques are rigid unless they may be defined by
             // the current body.
-            TypingMode::Analysis { defining_opaque_types: non_rigid_opaques }
+            TypingMode::Analysis {
+                defining_opaque_types: non_rigid_opaques,
+                stalled_generators: _,
+            }
             | TypingMode::Borrowck { defining_opaque_types: non_rigid_opaques }
             | TypingMode::PostBorrowckAnalysis { defined_opaque_types: non_rigid_opaques } => {
                 !def_id.as_local().is_some_and(|def_id| non_rigid_opaques.contains(&def_id))

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

@@ -33,7 +33,7 @@ where
                 );
                 self.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
             }
-            TypingMode::Analysis { defining_opaque_types } => {
+            TypingMode::Analysis { defining_opaque_types, stalled_generators: _ } => {
                 let Some(def_id) = opaque_ty
                     .def_id
                     .as_local()

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

@@ -208,6 +208,21 @@ where
             }
         }
 
+        if let ty::CoroutineWitness(def_id, _) = goal.predicate.self_ty().kind() {
+            match ecx.typing_mode() {
+                TypingMode::Analysis { stalled_generators, defining_opaque_types: _ } => {
+                    if def_id.as_local().is_some_and(|def_id| stalled_generators.contains(&def_id))
+                    {
+                        return ecx.forced_ambiguity(MaybeCause::Ambiguity);
+                    }
+                }
+                TypingMode::Coherence
+                | TypingMode::PostAnalysis
+                | TypingMode::Borrowck { defining_opaque_types: _ }
+                | TypingMode::PostBorrowckAnalysis { defined_opaque_types: _ } => {}
+            }
+        }
+
         ecx.probe_and_evaluate_goal_for_constituent_tys(
             CandidateSource::BuiltinImpl(BuiltinImplSource::Misc),
             goal,