[ResultBuilder] Don't run syntactic diagnostics on transformed do statements

Visiting of transformed `do` shouldn't run syntatic diagnostics because
they are going to be performed by `visit` that called `visitDoStmt`.

Author: xedin

lib/Sema/CSSyntacticElement.cpp

@@ -1290,13 +1290,17 @@ class SyntacticElementSolutionApplication
   virtual ~SyntacticElementSolutionApplication() {}
 
 private:
-  ASTNode visit(Stmt *S) {
+
+  ASTNode visit(Stmt *S, bool performSyntacticDiagnostics = true) {
     auto rewritten = ASTVisitor::visit(S);
     if (!rewritten)
       return {};
 
-    if (auto *stmt = getAsStmt(rewritten))
-      performStmtDiagnostics(stmt, context.getAsDeclContext());
+    if (performSyntacticDiagnostics) {
+      if (auto *stmt = getAsStmt(rewritten)) {
+        performStmtDiagnostics(stmt, context.getAsDeclContext());
+      }
+    }
 
     return rewritten;
   }
@@ -1819,8 +1823,9 @@ class ResultBuilderRewriter : public SyntacticElementSolutionApplication {
 
 private:
   ASTNode visitDoStmt(DoStmt *doStmt) override {
-    if (auto transformed = transformDo(doStmt))
-      return visit(transformed.get());
+    if (auto transformed = transformDo(doStmt)) {
+      return visit(transformed.get(), /*performSyntacticDiagnostics=*/false);
+    }
 
     auto newBody = visit(doStmt->getBody());
     if (!newBody)

validation-test/Sema/SwiftUI/mixed_swiftui_and_multistatement_closures.swift

@@ -35,8 +35,8 @@ struct MyView : View {
         switch (status) {
         case .complete:
           ForEach(items, id: \.self) { item in
-            if let question = item.question,
-               let answer = item.answer {
+            if let question = item.question, // expected-error {{initializer for conditional binding must have Optional type, not 'String'}}
+               let answer = item.answer {    // expected-error {{initializer for conditional binding must have Optional type, not 'Int'}}
               ItemView {
                 currItem.question = question
                 currItem.answer = answer