Run all MatchType reduction under Mode.Type #17937
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There are a number of calls to ".simplified", which changes behaviour based on Mode.Type. It does _less_ under Mode.Type, so we conservatively call it all under Mode.Type. Transcribing and paraphrasing from smarter's comment in scala#16408 (comment) : Type erasure assumes method signatures aren't simplified, since simplification logic is implementation-defined. For instance, some intersection types can be simplified down, but intersection types and their simplification can erase to different types - prefering classes over traits, for instance (for Java interop, as it matches Java's erasure). Also note, simplify doesn't simplify intersections and unions in Type mode. But Match Types will cache their reduction without considering the type mode as a cache input, thus the simplified reduction leaks even when called in Type mode. So we call simplified in Mode.Type, in both cases (another desire), so only that result is cached instead. Using normalise doesn't work because, for example, that doesn't normalise match types that are applied type args (e.g. args of Pair). And not caching the result of those reductions means that they'll get repeat over and over.
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I look forward to a nightly build or something where I can try this out :-) |
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Transcribing and paraphrasing from @smarter's comment in
#16408 (comment) :
Type erasure assumes method signatures aren't simplified, since
simplification logic is implementation-defined. For instance, some
intersection types can be simplified down, but intersection types and
their simplification can erase to different types - prefering classes
over traits, for instance (for Java interop, as it matches Java's
erasure).
Also note, simplify doesn't simplify intersections and unions in Type
mode. But Match Types will cache their reduction without considering
the type mode as a cache input, thus the simplified reduction leaks even
when called in Type mode.
So we call simplified in Mode.Type, in both cases (another desire), so
only that result is cached instead.
Using normalise doesn't work because, for example, that doesn't
normalise match types that are applied type args (e.g. args of Pair).
And not caching the result of those reductions means that they'll get
repeat over and over.