Generalizing keypath-to-function conversions

[ensan-hcl (ensan)]

I'd like this bug(?) to be also fixed, when you generalize the conversion between keypath and function.

Key Paths as function: Why doesn't this code work?

https://github.com/apple/swift-evolution/blob/master/proposals/0249-key-path-literal-function-expressions.md SE-0249 introduced key path literal as function. Following code works well. let count: (String) -> Int = \String.count count("Hey") // 3 However, using this feature directly is not possible. \String.count("Hey") error: repl.swift:3:9: error: invalid component of Swift key path \String.count("Hey") ^ error: repl.swift:3:1: error: key path must have at least one component \Str…