Rely on variance to typecheck more uses of wildcards #6719
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If we can't capture the wildcard argument, we might still be able to return true to the subtype check by approximating the wildcard based on variance. This leads to a regression in t5729 were two overloads are now considered ambiguous, but the only reason they were not ambiguous before was that the subtype test failed when it shouldn't, so this seems acceptable.
Because of the previous commit, tests/fuzzy/AE-9a131723f09b9f77c99c52b709965e580a61706e.scala now passes the typer, but then crashes in ExpandSAMs because we attempt to create an anonymous class whose parent is `PartialFunction[_, Int]` and tpd.ClassDef does not handle wildcard arguments. We avoid this issue by getting the argument types for the parent from the closure DefDef whose parameter and result types can never be wildcards.
odersky
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Jun 21, 2019
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If we can't capture the wildcard argument, we might still be able to
return true to the subtype check by approximating the wildcard based on
variance.