[astgen] Add test to prevent regressions.

Author: zoecarver

lib/Parse/ParseDecl.cpp

@@ -167,7 +167,7 @@ extern "C" void parseTopLevelSwift(const char *buffer,
                                    void (*)(void *, void *));
 
 static void appendToVector(void *declPtr, void *vecPtr) {
-  auto vec = static_cast<SmallVectorImpl<Decl *> *>(vecPtr);
+  auto vec = static_cast<SmallVectorImpl<ASTNode> *>(vecPtr);
   auto decl = static_cast<Decl *>(declPtr);
 
   vec->push_back(decl);

test/ASTGen/verify-parse.swift

@@ -0,0 +1,21 @@
+// RUN: %target-run-simple-swift(-enable-experimental-feature SwiftParser -enable-experimental-feature ParserASTGen)
+
+func test1(x: Int, fn: (Int) -> Int) -> Int {
+  let xx = fn(42)
+  return fn(x)
+}
+
+func test2(b: Bool) {
+  if b {
+    print("TRUE")
+  } else {
+    print("FALSE")
+  }
+
+  let x = true
+}
+
+func test3(y: Int) -> Int {
+  let x = y
+  return x
+}