Narrowing dict | Literal does not work in Mypy 1.5.0

[zroug]

Bug Report

When using Mypy 1.5.0, expressions like dict | Literal[""] don't narrow correctly:

To Reproduce

from typing import Literal

x: Literal[""] | dict
y: Literal[""] | list

if x == "":
    reveal_type(x)

if y == "":
    reveal_type(y)

Mypy 1.4.1
Mypy 1.5.0

Expected Behavior

Both revealed types should be Literal[""]. (As in Mypy 1.4.1.)

Actual Behavior

Mypy 1.5.0 does not narrow the revealed type for x. y gets narrowed correctly.

Your Environment

See Playground links.

[atugushev]

It appears to be fixed in the master branch.

[zroug]

Oh great, when I created the issue it wasn't fixed on master yet, but now it seems to be fixed indeed. I don't know if you want to keep this issue open for visibility until this is released or not, so feel free to close it as you see fit.

[hauntsaninja]

Looks like the original regression was in a typeshed sync 59a6c5e. Specifically, the addition of __eq__ to Mapping in python/typeshed#10297

diff --git a/mypy/typeshed/stdlib/typing.pyi b/mypy/typeshed/stdlib/typing.pyi
index db042dc44..08d7da5e8 100644
--- a/mypy/typeshed/stdlib/typing.pyi
+++ b/mypy/typeshed/stdlib/typing.pyi
@@ -631,6 +631,7 @@ class Mapping(Collection[_KT], Generic[_KT, _VT_co]):
     def keys(self) -> KeysView[_KT]: ...
     def values(self) -> ValuesView[_VT_co]: ...
     def __contains__(self, __key: object) -> bool: ...
+    def __eq__(self, __other: object) -> bool: ...

This recently got fixed by #15837, but perhaps unintentionally

[ilevkivskyi]

I don't think we need to keep this open. There is little chance #15837 can be included in 1.5.1 (it is quite a major change), so you will need to wait for 1.6.0