Mark Lacey 5c6c7ff651 Disallow conversions from IUOs to extistentials. ...

Commit 170dc8acd7 removed a penalty that
we used to have for conversions to Any. In some unusual circumstances
not having that penalty can result in new amiguities where we should
have nothing ambiguous about an expression according to our type rules.

This change attempts to ensure that we make that less likely or
impossible by not allowing direct conversions from IUOs to Any (instead
forcing these to first be force-unchecked, leading to more expensive
solutions). We never should have allowed these conversions anyway,
independent of removing the penalty for conversions to Any.

This change is intentionally very narrow to avoid further potential
source breakage.

Fixes rdar://problem/29907555.

2017-01-12 16:45:53 -08:00

164 KiB

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