Fix exttype inheritance from builtin bytearray type.

Closes #2106.

CHANGES.rst

@@ -135,6 +135,9 @@ Bugs fixed
 * Cython no longer creates useless and incorrect ``PyInstanceMethod`` wrappers for
   methods in Python 3.  Patch by Jeroen Demeyer.  (Github issue #2105)
 
+* The builtin ``bytearray`` type could not be used as base type of cdef classes.
+  (Github issue #2106)
+
 Other changes
 -------------
 

Cython/Compiler/Builtin.py

@@ -391,6 +391,8 @@ def init_builtin_types():
         utility = builtin_utility_code.get(name)
         if name == 'frozenset':
             objstruct_cname = 'PySetObject'
+        elif name == 'bytearray':
+            objstruct_cname = 'PyByteArrayObject'
         elif name == 'bool':
             objstruct_cname = None
         elif name == 'Exception':

tests/run/bytearraymethods.pyx

@@ -275,3 +275,15 @@ def bytearray_append(bytearray b, signed char c, int i, object o):
     b.append(i)
     b.append(o)
     return b
+
+
+cdef class BytearraySubtype(bytearray):
+    """
+    >>> b = BytearraySubtype(b'abc')
+    >>> b._append(ord('x'))
+    >>> b.append(ord('y'))
+    >>> print(b.decode('ascii'))
+    abcxy
+    """
+    def _append(self, x):
+        self.append(x)