Sema: Retire disjunctions in trail instead of restoring in ~DisjunctionStep

Fixes #77008.

Author: slavapestov

lib/Sema/CSStep.cpp

@@ -425,9 +425,11 @@ StepResult ComponentStep::take(bool prevFailed) {
     case StepKind::Binding:
       return suspend(
           std::make_unique<TypeVariableStep>(*bestBindings, Solutions));
-    case StepKind::Disjunction:
+    case StepKind::Disjunction: {
+      CS.retireConstraint(disjunction);
       return suspend(
           std::make_unique<DisjunctionStep>(CS, disjunction, Solutions));
+    }
     case StepKind::Conjunction:
       return suspend(
           std::make_unique<ConjunctionStep>(CS, conjunction, Solutions));

lib/Sema/CSStep.h

@@ -684,16 +684,14 @@ class TypeVariableStep final : public BindingStep<TypeVarBindingProducer> {
 class DisjunctionStep final : public BindingStep<DisjunctionChoiceProducer> {
   Constraint *Disjunction;
   SmallVector<Constraint *, 4> DisabledChoices;
-  ConstraintList::iterator AfterDisjunction;
 
   std::optional<Score> BestNonGenericScore;
   std::optional<std::pair<Constraint *, Score>> LastSolvedChoice;
 
 public:
   DisjunctionStep(ConstraintSystem &cs, Constraint *disjunction,
                   SmallVectorImpl<Solution> &solutions)
-      : BindingStep(cs, {cs, disjunction}, solutions), Disjunction(disjunction),
-        AfterDisjunction(erase(disjunction)) {
+      : BindingStep(cs, {cs, disjunction}, solutions), Disjunction(disjunction) {
     assert(Disjunction->getKind() == ConstraintKind::Disjunction);
     pruneOverloadSet(Disjunction);
     ++cs.solverState->NumDisjunctions;
@@ -702,8 +700,6 @@ class DisjunctionStep final : public BindingStep<DisjunctionChoiceProducer> {
   ~DisjunctionStep() override {
     // Rewind back any changes left after attempting last choice.
     ActiveChoice.reset();
-    // Return disjunction constraint back to the system.
-    restore(AfterDisjunction, Disjunction);
     // Re-enable previously disabled overload choices.
     for (auto *choice : DisabledChoices)
       choice->setEnabled();

test/Constraints/issue-77008.swift

@@ -0,0 +1,5 @@
+// RUN: not %target-swift-frontend -typecheck %s
+
+// Just don't crash.
+
+Binding<Bool>Binding<Bool>