Slava Pestov a3cad02708 Sema: Stricter superclass constraints when opening a generic signature ...

A generic signature like <T : SomeClass> would create
a subtype constraint between the type variable for T and
SomeClass. This is too loose, because a subclass existential
like 'SomeClass & SomeProto' is a subtype of SomeClass, but
cannot bind to T, because it is not representationally a
single retainable pointer.

Fixes <rdar://problem/32617814>, <https://bugs.swift.org/browse/SR-5142>.

2017-07-24 22:58:04 -07:00

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