[ConstraintSystem] Make it possible to determine that closure is in result builder context

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -5287,6 +5287,10 @@ class ConstraintSystem {
   /// part of the constraint system.
   void forEachExpr(Expr *expr, llvm::function_ref<Expr *(Expr *)> callback);
 
+  /// Determine whether one of the parent closures the given one is nested
+  /// in (if any) has a result builder applied to its body.
+  bool isInResultBuilderContext(ClosureExpr *closure) const;
+
   SWIFT_DEBUG_DUMP;
   SWIFT_DEBUG_DUMPER(dump(Expr *));
 

lib/Sema/CSClosure.cpp

@@ -919,6 +919,19 @@ bool ConstraintSystem::generateConstraints(ClosureExpr *closure) {
   return false;
 }
 
+bool ConstraintSystem::isInResultBuilderContext(ClosureExpr *closure) const {
+  if (!closure->hasSingleExpressionBody()) {
+    auto *DC = closure->getParent();
+    do {
+      if (auto *parentClosure = dyn_cast<ClosureExpr>(DC)) {
+        if (resultBuilderTransformed.count(parentClosure))
+          return true;
+      }
+    } while ((DC = DC->getParent()));
+  }
+  return false;
+}
+
 bool isConditionOfStmt(ConstraintLocatorBuilder locator) {
   auto last = locator.last();
   if (!(last && last->is<LocatorPathElt::Condition>()))