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Fix a compiler assertion crash #16291

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Merged
merged 1 commit into from
Nov 25, 2022
Merged

Fix a compiler assertion crash #16291

merged 1 commit into from
Nov 25, 2022

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dwijnand
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@dwijnand dwijnand commented Nov 7, 2022 •
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@dwijnand dwijnand linked an issue Nov 7, 2022 that may be closed by this pull request
ICE: java.lang.AssertionError: assertion failed: invalid prefix HKTypeLambda(List(T), ...,List(TypeParamRef(T)))), at dotty.tools.dotc.core.Types$NamedType.<init>(Types.scala:2043) #12448
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@dwijnand dwijnand marked this pull request as ready for review November 7, 2022 10:26
@dwijnand dwijnand requested a review from prolativ November 7, 2022 10:27
smarter
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@dwijnand dwijnand marked this pull request as draft November 7, 2022 16:22
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@dwijnand dwijnand marked this pull request as ready for review November 8, 2022 08:35
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compiler/src/dotty/tools/dotc/core/Types.scala Outdated
@@ -2633,7 +2633,8 @@ object Types {
}
}
if (prefix.isInstanceOf[WildcardType]) WildcardType
else withPrefix(prefix)
else if prefix.isValueTypeOrWildcard || (prefix eq NoPrefix) then withPrefix(prefix)
else typer.ErrorReporting.errorType(i"Cannot ($this).deriveSelect($prefix)", ctx.tree)
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This message shows up if I change mkArray[Array] to val x = mkArray[Array] so a more user-friendly message would be nicer.

I was trying to see if we could catch the problem earlier but it's a bit tricky. The problem is that when the prefix is erroneous we still create dummy denotations in findMember: https://github.com/lampepfl/dotty/blob/970d1191ae61dbcc2c10f55ee749c946e35d57db/compiler/src/dotty/tools/dotc/core/Types.scala#L725-L726
If we just drop this case and return a NoDenotation then we avoid these complications, but that could maybe lose information.

Otherwise we could try to handle these error denotations better, but it's tricky because newErrorSymbol actually wraps the ErrorType in a TypeAlias when the member is a type, and Type#isError doesn't check that.

@dwijnand dwijnand assigned smarter and unassigned prolativ Nov 23, 2022
@dwijnand dwijnand requested a review from smarter November 23, 2022 08:53
@dwijnand dwijnand merged commit ce38da4 into scala:main Nov 25, 2022
@dwijnand dwijnand deleted the assertion-crash branch November 25, 2022 11:27
@Kordyjan Kordyjan added this to the 3.3.0 milestone Aug 1, 2023
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