swift234

Implement subtyping rules that allow one to convert a function type to
another function type, so long as the source is a subtype of the
target. The subtyping relation is fairly obvious, allowing parameter
renaming, qualification conversions for lvalue types, and
protocol-conformance conversions (at the top level of function
types). It is a strict subset of the allowed type coercions.

The representation of FunctionConversionExpr is temporary. It will
need to account for the capture of the source of the conversion in the
trivial-trivial case.



Swift SVN r1839