Mark Lacey 54b2504699 [ConstraintSystem] Fix a logic error in computing potential bindings. ...

A change was made to attempt to use constraints that we have between
type variables to inform potential bindings, such that if we have:
   $T1 <: $T2
we would use $T1's bindings to add to the bindings of $T2. This is
only valid if we're adding bindings where $T1 is the supertype,
though, otherwise we could have the constraints:
  $T1 <: $T2
  $T1 <: X
imply that $T2 is a supertype of X, which doesn't make sense.

Fixes rdar://problem/40810000 (aka https://bugs.swift.org/browse/SR-7875).

2018-06-18 18:33:30 -07:00

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