Doug Gregor ecfea608db [Type checker] Classify the various optional conversion kinds. ...

1efafbcd9b restricted our classification
of various optional-related conversions (implicit forcing of IUOs,
optional-to-optional conversions, value-to-optional conversions) to
produce a single potential classification. However, in the presence of
type variables, we cannot always determine which particular conversion
restriction might apply. Prior to 1efafb, we produced too many
options; after 1efafb, we produced too few. Here, enumerate a more
bounded (but complete) set of potential conversions, taking into
account embedded type variables.

This is a better fix for rdar://problem/29977523 than simply reverting
1efafb, because it bounds the set of optional conversions we attempt.

2017-01-17 13:10:26 -08:00

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