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Fix #21669: Check parents non-empty before calling reduceLeft #21673

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Merged
merged 2 commits into from
Oct 5, 2024
Merged

Fix #21669: Check parents non-empty before calling reduceLeft #21673

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8f4210e
Check parents non-empty before calling reduceLeft
noti0na1 Sep 30, 2024
63e42d3
Add assertion to ensure: if the parents of a module is empty, it must…
noti0na1 Oct 3, 2024
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4 changes: 3 additions & 1 deletion compiler/src/dotty/tools/dotc/typer/Applications.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1962,7 +1962,9 @@ trait Applications extends Compatibility {

def widenPrefix(alt: TermRef): Type = alt.prefix.widen match
case pre: (TypeRef | ThisType) if pre.typeSymbol.is(Module) =>
pre.parents.reduceLeft(TypeComparer.andType(_, _))
val ps = pre.parents
if ps.isEmpty then pre
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I believe it's an invariant that parents of modules are non-empty. except if the module is a package. We should not ignore that invariant here. So before returning pre, let's add the assertion

assert(pre.typeSymbol.is(Package), pre)

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Actually, that's an invariant of if the module has been entered. But it could be wrong before. Anyway, it's an important invariant so I think we should not ignore it here, and catch any errors in importSuggestions instead.

else ps.reduceLeft(TypeComparer.andType(_, _))
case wpre => wpre

/** If two alternatives have the same symbol, we pick the one with the most
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