Open Radar

 
Summary:
Backticks to enable the use of keywords as ordinary symbols don’t work in closures with implicit arguments and returns.


Steps to Reproduce:
1. Compile this:
struct S {}
func `if`(S) -> S { return S() }
func g(S -> S) {}
func h() {
	g { `if`($0) }
}


Expected Results:
Compilation.


Actual Results:
Errors:
boom.swift:5:9: error: expected expression, var, or let in 'if' condition
        g { `if`($0) }
               ^
boom.swift:5:2: error: cannot invoke 'g' with an argument list of type '(() -> _)'
        g { `if`($0) }
        ^
boom.swift:5:4: note: expected an argument list of type '(S -> S)'
        g { `if`($0) }
          ^


Regression:
This doesn’t happen if:
1. you add a `return` keyword to the closure.
2. you use a first-order value instead of a closure, i.e. f(`if`(S())) where f : S -> ().
3. you use a named parameter.
4. you pass `if` directly as a referent instead of closing over it, i.e. f(`if`) where f : (S -> S) -> ().
5. you get fed up and name the function something else instead. Haha, as if that would ever happen!


Notes:
N/A