Delay hard argument comparisons #20007
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When comparing arguments of two applied types, perform hard comparisons after easy ones. A comparison if hard if it entails a subtype test A <: B where A is an AndType or B is an OrType. Such comparisons need to perform an either, which might lose solutions. Fixes scala#19999
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We could possibly generalize this, delaying hard comparisons in more conjunctive tests, not just type in arguments. But it is hard in general to identify a conjunctive subsequence of tests when doing a subtype traversal. |
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Interesting! I've had a case that required this defer too. |
smarter
approved these changes
Mar 25, 2024
| * So we defer such tests to run last, on the chance that some other argument | ||
| * comparison will instantiate or constrain type variables first. | ||
| */ | ||
| def isHard(arg1: Type, arg2: Type): Boolean = |
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Using the word hard here might lead to confuse with hard unions since OrTypes are also involved. Maybe we could call this isIncomplete instead?
smarter
approved these changes
Mar 25, 2024
Co-authored-by: Guillaume Martres <[email protected]>
WojciechMazur
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Jul 5, 2024
Backports #20007 to the LTS branch. PR submitted by the release tooling. [skip ci]
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When comparing arguments of two applied types, perform hard comparisons after easy ones. A comparison is hard if it entails a subtype test A <: B where A is an AndType or B is an OrType. Such comparisons need to perform an either, which might lose solutions.
Fixes #19999