Doug Gregor 4cc41e5e64 [Constraint solver] Perform the "occurs" check properly. ...

We've been performing the "occurs" check when computing potential
bindings for type variables, but we weren't actually performing the
check for bindings that *must* occur. Perform the occurs check before
binding type variables, which fixes a few crashers and is far more principled.

Note that this obviates the need for tracking the type variables we've
substituted in simplifyType(), so simplify that as well.

Fixes rdar://problem/27879334 / SR-2351.

2016-10-25 13:32:06 -07:00

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