Sema: Record pack expansion environments in the trail

lib/Sema/CSTrail.cpp

@@ -201,6 +201,14 @@ SolverTrail::Change::recordedOpenedPackExpansionType(PackExpansionType *expansio
   return result;
 }
 
+SolverTrail::Change
+SolverTrail::Change::recordedPackExpansionEnvironment(ConstraintLocator *locator) {
+  Change result;
+  result.Kind = ChangeKind::RecordedPackExpansionEnvironment;
+  result.Locator = locator;
+  return result;
+}
+
 void SolverTrail::Change::undo(ConstraintSystem &cs) const {
   auto &cg = cs.getConstraintGraph();
 
@@ -277,6 +285,10 @@ void SolverTrail::Change::undo(ConstraintSystem &cs) const {
   case ChangeKind::RecordedOpenedPackExpansionType:
     cs.removeOpenedPackExpansionType(ExpansionTy);
     break;
+
+  case ChangeKind::RecordedPackExpansionEnvironment:
+    cs.removePackExpansionEnvironment(Locator);
+    break;
   }
 }
 
@@ -424,6 +436,12 @@ void SolverTrail::Change::dump(llvm::raw_ostream &out,
     ExpansionTy->print(out, PO);
     out << ")\n";
     break;
+
+  case ChangeKind::RecordedPackExpansionEnvironment:
+    out << "(recorded pack expansion environment at ";
+    Locator->dump(&cs.getASTContext().SourceMgr, out);
+    out << ")\n";
+    break;
   }
 }