Backport "Fix #20897: Make Nothing ⋔ Nothing, as per spec." to LTS
#22077
Conversation
This file contains 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
`derivesFrom`, used in `provablyDisjointClasses`, normally returns `false` when the receiver is `Nothing`. However, it returns `true` if the right-hand-side happens to be exactly `Nothing` as well. For the purpose of computing `provablyDisjoint`, that is not what we want. The root issue was that we let the previous algorithm handle `Nothing` like a class type, which it *is* in dotc but not in the spec. That led to this mistake. `AnyKind` suffers a similar issue, but already had special-cases in various places to mitigate it. Instead of adding a new special-case for `Nothing` inside `provablyDisjointClasses`, we address the root issue. Now we deal with `Nothing` and `AnyKind` early, before trying any of the code paths that handle (real) class types. [Cherry-picked b7846c4][modified]
|
No regressions detected in the community build up to backport-lts-3.3-21343. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
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Outdated suggestions cannot be applied.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.
Backports #21241 to the 3.3.5.
PR submitted by the release tooling.
[skip ci]