Fix i11545 #12087
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Fix i11545 #12087
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If we do decide to merge this, I'll open a new issue for investigating in detail what is the exact problem here, and how to fix it well. |
odersky
requested changes
Apr 14, 2021
| // if base is a disjunction, this might have come from a tp1 type that | ||
| // expands to a match type. In this case, we should try to reduce the type | ||
| // and compare the redux. This is done in fourthTry | ||
| def tryBaseType(cls2: Symbol): Boolean = { |
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This looks like it will overshoot. tryBaseType is an essential element for comparisons. Simply ignoring this step under GADT constraint inference is too drastic. I would expect instead a necessaryEither somewhere in the logic.
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We only avoid tryBaseType if the LHS is an AndType. In that case, using the base type can end up performing a comparison that is too approximate to be useful for GADTs (see neg/i11545a.scala, added in this PR). I have ideas for other fixes, we can discuss them during today's lab meeting.
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Duplicate of #15175 |
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This is more of a makeshift fix than anything else. If we care about plugging the soundness hole for 3.0.0, then we should merge it. Otherwise, I'll have to spend a bit more time fiddling with TypeComparer in order to properly fix the issue.