Address code review

Author: Guido van Rossum

mypy/semanal.py

@@ -903,7 +903,7 @@ def analyze_base_classes(self, defn: ClassDef) -> None:
         base_types = []  # type: List[Instance]
         info = defn.info
 
-        base_type_exprs = self.get_base_type_exprs(defn)
+        base_type_exprs = self.check_with_metaclass(defn)
         for base_expr in base_type_exprs:
             try:
                 base = self.expr_to_analyzed_type(base_expr)
@@ -955,9 +955,9 @@ def analyze_base_classes(self, defn: ClassDef) -> None:
         if defn.info.is_enum and defn.type_vars:
             self.fail("Enum class cannot be generic", defn)
 
-    def get_base_type_exprs(self, defn: ClassDef) -> List[Expression]:
-        # Special-case six.with_metaclass(M, B1, B2, ...)
-        # TODO: factor out in helper method
+    def check_with_metaclass(self, defn: ClassDef) -> List[Expression]:
+        # Special-case six.with_metaclass(M, B1, B2, ...).
+        # May update defn.metaclass.
         base_type_exprs = defn.base_type_exprs
         if defn.metaclass is None and len(base_type_exprs) == 1:
             base_expr = base_type_exprs[0]

test-data/unit/check-classes.test

@@ -3158,6 +3158,24 @@ class M(type):
 class A(with_metaclass(M)): pass
 reveal_type(type(A).x)  # E: Revealed type is 'builtins.int'
 
+[case testSixWithMetaclassImportFrom]
+import six
+from metadefs import M
+class A(six.with_metaclass(M)): pass
+reveal_type(type(A).x)  # E: Revealed type is 'builtins.int'
+[file metadefs.py]
+class M(type):
+    x = 5
+
+[case testSixWithMetaclassImport]
+import six
+import metadefs
+class A(six.with_metaclass(metadefs.M)): pass
+reveal_type(type(A).x)  # E: Revealed type is 'builtins.int'
+[file metadefs.py]
+class M(type):
+    x = 5
+
 [case testSixWithMetaclassAndBase]
 import six
 class M(type):
@@ -3180,10 +3198,12 @@ C2().baz()  # E: "C2" has no attribute "baz"
 import six
 class M(type): pass
 class A(object): pass
+def f() -> type: return M
 class C1(six.with_metaclass(M), object): pass  # E: Invalid base class
 class C2(C1, six.with_metaclass(M)): pass  # E: Invalid base class
 class C3(six.with_metaclass(A)): pass  # E: Metaclasses not inheriting from 'type' are not supported
 class C4(six.with_metaclass(M), metaclass=M): pass  # E: Invalid base class
+class C5(six.with_metaclass(f())): pass  # E: Dynamic metaclass not supported for 'C5'
 
 [case testSixWithMetaclassErrors_python2-skip]
 # No error here yet