Fix bug when narrowing union containing custom eq against custom eq #20754
+49
−1
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Contributor
|
Diff from mypy_primer, showing the effect of this PR on open source code: pip (https://github.com/pypa/pip)
+ src/pip/_internal/resolution/resolvelib/candidates.py:293: error: Item "None" of "Link | None" has no attribute "is_wheel" [union-attr]
+ src/pip/_internal/resolution/resolvelib/candidates.py:293: error: Item "None" of "Link | None" has no attribute "is_file" [union-attr]
+ src/pip/_internal/resolution/resolvelib/candidates.py:294: error: Item "None" of "Link | None" has no attribute "filename" [union-attr]
+ src/pip/_internal/resolution/resolvelib/candidates.py:305: error: Item "None" of "Link | None" has no attribute "is_wheel" [union-attr]
+ src/pip/_internal/resolution/resolvelib/candidates.py:306: error: Item "None" of "Link | None" has no attribute "is_file" [union-attr]
schema_salad (https://github.com/common-workflow-language/schema_salad)
+ schema_salad/tests/test_examples.py: note: In function "test_scoped_id":
+ schema_salad/tests/test_examples.py:395:23: error: Argument 2 to "makerdf" has incompatible type "int | float | str | CommentedMap | CommentedSeq | None"; expected "CommentedMap | float | str | CommentedSeq" [arg-type]
+ schema_salad/tests/test_examples.py:408:23: error: Argument 2 to "makerdf" has incompatible type "int | float | str | CommentedMap | CommentedSeq | None"; expected "CommentedMap | float | str | CommentedSeq" [arg-type]
+ schema_salad/tests/test_examples.py:421:23: error: Argument 2 to "makerdf" has incompatible type "int | float | str | CommentedMap | CommentedSeq | None"; expected "CommentedMap | float | str | CommentedSeq" [arg-type]
+ schema_salad/tests/test_examples.py:434:23: error: Argument 2 to "makerdf" has incompatible type "int | float | str | CommentedMap | CommentedSeq | None"; expected "CommentedMap | float | str | CommentedSeq" [arg-type]
|
Collaborator
Author
|
Oh cool, for first time primer indicates we now actually do have a place where unsoundly special casing None could make sense |
Contributor
|
Tested: works. Thanks! |
Member
Do we have an issue about this so that we will not forget? Probably makes sense to do this before the next release, so that people will not see this as a perceived regression. |
ilevkivskyi
approved these changes
Feb 6, 2026
Collaborator
Author
|
It is easy to make changes now, I will just open a PR for it |
hauntsaninja
added a commit
to hauntsaninja/mypy
that referenced
this pull request
Feb 6, 2026
In python#20754 we see some primer hits where this unsoundness is beneficial
Collaborator
Author
|
Something like this should do it: #20756 |
hauntsaninja
added a commit
to hauntsaninja/mypy
that referenced
this pull request
Feb 6, 2026
In python#20754 we see some primer hits where this unsoundness is beneficial
Collaborator
Author
|
Oh and in general I am leaving some notes for myself in #20564 |
hauntsaninja
added a commit
that referenced
this pull request
Feb 6, 2026
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
I rewrote the logic for custom equality in #20643 . This is a soundness bug in that rewrite.
Fixes #20750