Sema: Strenghten invariants in SolverTrail::Change::undo()

Author: slavapestov

lib/Sema/CSSolver.cpp

@@ -1782,25 +1782,29 @@ ConstraintSystem::filterDisjunction(
       llvm::errs().indent(indent) << ")\n";
     }
 
-    if (restoreOnFail)
-      constraintsToRestoreOnFail.push_back(constraint);
-
     if (!constraint->isDisabled()) {
-      if (solverState)
+      if (restoreOnFail)
+        constraintsToRestoreOnFail.push_back(constraint);
+      else if (solverState)
         solverState->disableConstraint(constraint);
       else
         constraint->setDisabled();
     }
   }
 
-  switch (numEnabledTerms) {
-  case 0:
+  if (numEnabledTerms == 0)
+    return SolutionKind::Error;
+
+  if (restoreOnFail) {
     for (auto constraint : constraintsToRestoreOnFail) {
-      constraint->setEnabled();
+      if (solverState)
+        solverState->disableConstraint(constraint);
+      else
+        constraint->setDisabled();
     }
-    return SolutionKind::Error;
+  }
 
-  case 1: {
+  if (numEnabledTerms == 1) {
     // Only a single constraint remains. Retire the disjunction and make
     // the remaining constraint active.
     auto choice = disjunction->getNestedConstraints()[choiceIdx];
@@ -1849,9 +1853,7 @@ ConstraintSystem::filterDisjunction(
     return failedConstraint ? SolutionKind::Unsolved : SolutionKind::Solved;
   }
 
-  default:
-    return SolutionKind::Unsolved;
-  }
+  return SolutionKind::Unsolved;
 }
 
 // Attempt to find a disjunction of bind constraints where all options

lib/Sema/CSTrail.cpp

@@ -376,13 +376,12 @@ void SolverTrail::Change::undo(ConstraintSystem &cs) const {
     break;
 
   case ChangeKind::DisabledConstraint:
-    if (TheConstraint.Constraint->isDisabled())
-      TheConstraint.Constraint->setEnabled();
+    TheConstraint.Constraint->setEnabled();
     break;
 
   case ChangeKind::FavoredConstraint:
-    if (TheConstraint.Constraint->isFavored())
-      TheConstraint.Constraint->setFavored(false);
+    ASSERT(TheConstraint.Constraint->isFavored());
+    TheConstraint.Constraint->setFavored(false);
     break;
 
   case ChangeKind::RecordedResultBuilderTransform: