MessageBuilder.format_distinctly doesn't make identically named (but different) types distinct when one is generic

[OddBloke]

I've been playing around with the plugin interface, and was hitting a strange error with the following (minimal) example plugin:

from typing import Callable, Optional, Type

from mypy.plugin import MethodContext, Plugin


class DummyPlugin(Plugin):

    def get_method_hook(
            self, fullname: str) -> Optional[Callable[[MethodContext], Type]]:
        return dummy_callback


def dummy_callback(ctx: MethodContext) -> Type:
    return ctx.default_return_type


plugin = lambda _: DummyPlugin

dummy_plugin.py:8: error: Return type of "get_method_hook" incompatible with supertype "Plugin"
dummy_plugin.py:14: error: Incompatible return value type (got "Type", expected Type[Any])

It took a while of staring confusedly at my code to realise that the fix is quite simple:

--- dummy_plugin.py.old	2017-08-22 14:58:55.739834119 -0400
+++ dummy_plugin.py	2017-08-22 14:59:11.407829264 -0400
@@ -1,6 +1,7 @@
-from typing import Callable, Optional, Type
+from typing import Callable, Optional
 
 from mypy.plugin import MethodContext, Plugin
+from mypy.types import Type
 
 
 class DummyPlugin(Plugin):

It would be good to have a bit more information about where the types come from in this case.

[OddBloke]

Hmm, it looks like this is handled in the general case, I'm just hitting it because one of the types is generic (and so the string representations are different in the first comparison in MessageBuilder.format_distinctly).

Let me update the issue title.

[OddBloke]

I started looking at this, but I think it'll be much easier after #3430 has landed.

[gvanrossum]

Hm, maybe you can help with #3430? That PR seems to have ended up in a bit of quicksand...

[OddBloke]

Yep, I'll definitely take a look.

[ilevkivskyi]

I thin this one can be fixed now, since the PR superseding #3430 is now merged.

[OddBloke]

I don't think it is yet, that work was prerequisite to looking at this.

…

On Sat, 2 Sep 2017, 11:42 Ivan Levkivskyi ***@***.***> wrote: I thin this one can be fixed now, since the PR superseding #3430 <#3430> is now merged. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#3860 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAD1ECBYVUsy-_AML0D2ZCfM-iWaxI1sks5seTD4gaJpZM4O_DSk> .