Fix #11234: Avoid cycles in unifying F-bounded type parameters #11237
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
In tests/pos/11234.scala, we have the following F-bounded constraints:
bounds =
A0 <: Foo[LazyRef(A0)]
A <: Foo[LazyRef(A)]
ordering =
A <: A0
As `Foo[T]` is non-variant, at some point we will add `A0 <: A`, it
will trigger unification of `A0` and `A`. The unification will call
`Foo[A0].&(Foo[A])`, which in turn calls `TypeComparer.glb(Foo[A0],
Foo[A])`. The call `glb(Foo[A0], Foo[A])` in a fresh TypeComparer
will in turn add `A0 <: A` thus trigger the unification again.
We need to perform substitution before merge the bounds.
liufengyun
changed the title
odersky
approved these changes
Mar 4, 2021
|
Nice fix! |
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Outdated suggestions cannot be applied.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.
Fix #11234
In tests/pos/11234.scala, we have the following F-bounded constraints:
As
Foo[T]is non-variant, at some point we will addA0 <: A, itwill trigger unification of
A0andA. The unification will callFoo[A0].&(Foo[A]), which in turn callsTypeComparer.glb(Foo[A0], Foo[A]). The callglb(Foo[A0], Foo[A])in a fresh TypeComparerwill in turn add
A0 <: Athus trigger the unification again.We need to perform substitution before merging the bounds.