swift234

Infer the return type of a closure to be () if it contains no
return statements, or a return statement with no operand.

Also, fix a special-case diagnostic about converting a return
expression to (1) only apply to converting the actual return
expression, not an arbitrary sub-expression, and (2) use the
actual operand and return types, not the drilled-down types
that caused the failure.

Swift SVN r30420