[Clang] Do not consider a variadic function ellipsis part of a default arg (#153496)

When stashing the tokens of a parameter of a member function, we would
munch an ellipsis, as the only considered terminal conditions were `,`
and `)`.

Fixes #153445

clang/docs/ReleaseNotes.rst

@@ -209,6 +209,7 @@ Bug Fixes to C++ Support
   casts that are guaranteed to fail (#GH137518).
 - Fix bug rejecting partial specialization of variable templates with auto NTTPs (#GH118190).
 - Fix a crash when using ``explicit(bool)`` in pre-C++11 language modes. (#GH152729)
+- Fix the parsing of variadic member functions when the ellipis immediately follows a default argument.(#GH153445)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Parse/ParseCXXInlineMethods.cpp

@@ -1161,6 +1161,12 @@ bool Parser::ConsumeAndStoreInitializer(CachedTokens &Toks,
 
   while (true) {
     switch (Tok.getKind()) {
+    case tok::ellipsis:
+      // We found an elipsis at the end of the parameter list;
+      // it is not part of a parameter declaration.
+      if (ParenCount == 1 && NextToken().is(tok::r_paren))
+        return true;
+      goto consume_token;
     case tok::comma:
       // If we might be in a template, perform a tentative parse to check.
       if (!AngleCount)

clang/test/Parser/cxx-variadic-func.cpp

@@ -6,3 +6,24 @@ void f(...) {
 }
 
 void h(int n..., int m); // expected-error {{expected ')'}} expected-note {{to match}}
+
+
+namespace GH153445 {
+void f(int = {}...);
+
+struct S {
+  void f(int = {}...);
+  void g(int...);
+};
+
+void S::g(int = {}...) {}
+}
+
+
+template <typename ...T>
+constexpr int a() {return 1;}
+
+struct S2 {
+  template <typename ...Ts>
+  void f(int = a<Ts...>()...);
+};

clang/test/Parser/cxx2c-oxford-variadic-comma.cpp

@@ -36,6 +36,7 @@ void o(int x, ...);
 
 struct S {
   void p(this S...) {} // expected-warning {{declaration of a variadic function without a comma before '...' is deprecated}}
+  void f(int = {}...); // expected-warning {{declaration of a variadic function without a comma before '...' is deprecated}}
 };
 
 template<class ...Ts>