Perform typecheck for (typechecking) builtin casts.

Cython/Compiler/ExprNodes.py

@@ -8034,6 +8034,7 @@ class TypecastNode(ExprNode):
     #  operand      ExprNode
     #  base_type    CBaseTypeNode
     #  declarator   CDeclaratorNode
+    #  typecheck    boolean
     #
     #  If used from a transform, one can if wanted specify the attribute
     #  "type" directly and leave base_type and declarator to None
@@ -8094,7 +8095,7 @@ class TypecastNode(ExprNode):
             else:
                 warning(self.pos, "No conversion from %s to %s, python object pointer used." % (self.type, self.operand.type))
         elif from_py and to_py:
-            if self.typecheck and self.type.is_extension_type:
+            if self.typecheck and self.type.is_pyobject:
                 self.operand = PyTypeTestNode(self.operand, self.type, env, notnone=True)
             elif isinstance(self.operand, SliceIndexNode):
                 # This cast can influence the created type of string slices.

tests/run/typetest_T417.pyx

@@ -101,3 +101,14 @@ def test_getFooCast():
     cdef int old_count = count
     cdef Foo x = <Foo?>getFoo()
     return count - old_count
+
+def test_builtin_typecheck_cast(maybe_list):
+    """
+    >>> test_builtin_typecheck_cast([])
+    []
+    >>> test_builtin_typecheck_cast({})
+    Traceback (most recent call last):
+       ...
+    TypeError: Expected list, got dict
+    """
+    return <list?>maybe_list