Revert "Revert "Merge pull request swiftlang#26974 from rintaro/syntaxparse-roundtrip2""

This reverts commit 8df497d.

Author: rintaro

lib/Parse/ParseDecl.cpp

@@ -4097,8 +4097,10 @@ parseDeclTypeAlias(Parser::ParseDeclOptions Flags, DeclAttributes &Attributes) {
   Status |= parseIdentifierDeclName(
       *this, Id, IdLoc, "typealias",
       [](const Token &next) { return next.isAny(tok::colon, tok::equal); });
-  if (Status.isError())
+  if (Status.isError()) {
+    TmpCtxt->setTransparent();
     return nullptr;
+  }
 
   DebuggerContextChange DCC(*this, Id, DeclKind::TypeAlias);
 

test/Syntax/round_trip_misc.swift

@@ -22,6 +22,9 @@ do {
 do {
   typealias Alias3 = () -> @objc func
 }
+do {
+  typealias
+}
 
 // Orphan '}' at top level
 }