Doug Gregor 17669d7d5d [Trailing closures] Attempt both forward and backward scans. ...

To better preserve source compatibility, teach the constraint
solver to try both the new forward scanning rule as well as the
backward scanning rule when matching a single, unlabeled trailing
closure. In the extreme case, where the unlabeled trailing closure
matches different parameters with the different rules, and yet both
produce a potential match, introduce a disjunction to explore both
possibilities.

Prefer solutions that involve forward scans to those that involve
backward scans, so we only use the backward scan as a fallback.

2020-07-24 08:11:25 -07:00

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