[AST] Enforce that ParenExpr is typed as ParenType

Make sure we don't accidentally drop the sugar of
the type.

Author: hamishknight

lib/AST/ASTVerifier.cpp

@@ -2008,6 +2008,15 @@ class Verifier : public ASTWalker {
       verifyCheckedBase(E);
     }
 
+    void verifyChecked(ParenExpr *E) {
+      PrettyStackTraceExpr debugStack(Ctx, "verifying ParenExpr", E);
+      if (!isa<ParenType>(E->getType().getPointer())) {
+        Out << "ParenExpr not of ParenType\n";
+        abort();
+      }
+      verifyCheckedBase(E);
+    }
+
     void verifyChecked(AnyTryExpr *E) {
       PrettyStackTraceExpr debugStack(Ctx, "verifying AnyTryExpr", E);
 

test/expr/closure/nested_inner_closures.swift

@@ -5,3 +5,4 @@ assert({ () -> Bool in
 }(), "")
 
 var x = ({ () -> String in return "s" })()
+var y = ((({ () -> String in return "s" })))()