C++, fix bug in type alias parsing.

Fixes sphinx-doc/sphinx#2061

sphinx/domains/cpp.py

@@ -1829,7 +1829,7 @@ class ASTTypeUsing(ASTBase):
         self.type = type
 
     def get_id_v1(self, objectType=None, symbol=None):
-        return None
+        raise NoOldIdError()
 
     def get_id_v2(self, objectType=None, symbol=None):
         return symbol.get_full_nested_name().get_id_v2()
@@ -3198,11 +3198,13 @@ class DefinitionParser(object):
 
         if objectType == 'type':
             error = None
+            pos = self.pos
             try:
                 if not templatePrefix:
                     declaration = self._parse_type(named=True, outer='type')
             except DefinitionError as e:
                 error = e.description
+                self.pos = pos
             try:
                 if not declaration:
                     declaration = self._parse_type_using()

tests/test_domain_cpp.py

@@ -246,6 +246,8 @@ def test_type_definitions():
     check('enumerator', 'A = std::numeric_limits<unsigned long>::max()',
           None, "1A")
 
+    check('type', 'A = B', None, '1A')
+
 
 def test_fundamental_types():
     # see http://en.cppreference.com/w/cpp/language/types