Narrowing dict | Literal does not work in Mypy 1.5.0

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.

It appears to be fixed in the master branch.

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.

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

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

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Narrowing `dict | Literal` does not work in Mypy 1.5.0 #15860

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Narrowing dict | Literal does not work in Mypy 1.5.0 #15860

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atugushev commented on Aug 15, 2023

zroug commented on Aug 15, 2023

hauntsaninja commented on Aug 16, 2023

ilevkivskyi commented on Aug 16, 2023

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Narrowing `dict | Literal` does not work in Mypy 1.5.0 #15860