Pavel Yaskevich 71753f3ca6 [ConstraintSystem] Rank contextually unavailable overloads lower than other choices (#29921) ...

Currently constraint solver is only capable of detecting universally unavailable
overloads but that's insufficient because it's still possible to pick a contextually
unavailable overload choice which could be better than e.g. generic overload, or
one with defaulted arguments, marked as disfavored etc.

Let's introduce `ConstraintSystem::isDeclUnavailable` which supports both universal
and contextual unavailability and allow constraint solver to rank all unavailable
overload choices lower than any other possible choice(s).

Resolves: rdar://problem/59056638

2020-02-19 13:13:53 -05:00

961 B

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