Similar to r11235, but for 'is' expressions. QoI suffers somewhat here
because (1) we don't have an easy way to specialize the diagnostic,
and (2) we can't fix up the broken constraint system when we hit a
problem.
Swift SVN r11241
Previously, we had an artificial separation between the subexpression
"x" and the context of the expression "x as T". This breaks down when
the subexpression includes a reference to an anonymous closure
argument (e.g., $0) from a single-expression closure. By merging the
systems, we fix the crasher (<rdar://problem/15633178>) and allow
improved type inference for these expressions.
Swift SVN r11235
Notice that I'm hacking the test to get it running again. I'd normally
feel bad about this, but since labeled tuple elements are going away,
the class of problems this commit is working around will disappear
entirely.
Swift SVN r11115
