Allow instances of a class to access inner class definitions on that class. (#3636)

This fixes #3635

Author: rowillia

mypy/checkmember.py

@@ -227,6 +227,13 @@ def analyze_member_var_access(name: str, itype: Instance, info: TypeInfo,
         # The associated Var node of a decorator contains the type.
         v = vv.var
 
+    if isinstance(vv, TypeInfo):
+        # If the associated variable is a TypeInfo synthesize a Var node for
+        # the purposes of type checking.  This enables us to type check things
+        # like accessing class attributes on an inner class.
+        v = Var(name, type=type_object_type(vv, builtin_type))
+        v.info = info
+
     if isinstance(v, Var):
         return analyze_var(name, v, itype, info, node, is_lvalue, msg,
                            original_type, not_ready_callback, chk=chk)

test-data/unit/check-classes.test

@@ -681,6 +681,21 @@ def produce() -> Bar:
     reveal_type(Bar().make_int)  # E: Revealed type is 'def () -> builtins.int'
     return Bar()
 
+[case testInnerClassPropertyAccess]
+class Foo:
+    class Meta:
+        name = 'Bar'
+    meta = Meta
+
+reveal_type(Foo.Meta)  # E: Revealed type is 'def () -> __main__.Foo.Meta'
+reveal_type(Foo.meta)  # E: Revealed type is 'def () -> __main__.Foo.Meta'
+reveal_type(Foo.Meta.name)  # E: Revealed type is 'builtins.str'
+reveal_type(Foo.meta.name)  # E: Revealed type is 'builtins.str'
+reveal_type(Foo().Meta)  # E: Revealed type is 'def () -> __main__.Foo.Meta'
+reveal_type(Foo().meta)  # E: Revealed type is 'def () -> __main__.Foo.Meta'
+reveal_type(Foo().meta.name)  # E: Revealed type is 'builtins.str'
+reveal_type(Foo().Meta.name)  # E: Revealed type is 'builtins.str'
+
 -- Declaring attribute type in method
 -- ----------------------------------