[SR-504] Functions with default values cannot be called as parameters

[swift-ci]

Previous ID	SR-504
Radar	rdar://problem/51939453
Original Reporter	Yoontsaw (JIRA User)
Type	Bug

Attachment: Download

Environment

OS X 10.11, Xcode(swift 2.1)/REPL(swift 2.2-dev)

Additional Detail from JIRA

Votes	1
Component/s	Compiler
Labels	Bug, TypeChecker
Assignee	None
Priority	Medium

md5: b01e85e40f3b2a14293af5843699a96c

is duplicated by:

• SR-4878 Allow mapping of signatures with defaulted arguments
• SR-749 References to functions do not include default parameters

Issue Description:

When I create a function like the codes below, when I call this function, the IDE actually gives two candidates, one of which is of type Int -> Int, and the other of type (Int, Int) -> Int.
But when I want to feed this function as a parameter of another function, the "Int -> Int" one is not working and produces the error as below.

  1> func tested(x: Int, y: Int = 0) -> Int { return x + y } 
  2. func testor(f: (Int) -> Int, x: Int) -> Int { return f(x) } 
  3. testor(tested, x: 0)
rep.swift:3:8: error: cannot convert value of type '(Int, y: Int) -> Int' to expected argument type '(Int) -> Int'
testor(tested, x: 0)
       ^~~~~~

This bug causes big problem when the parameter function is pre-defined with default values. When you see multiple overloads of that function e.g. Int tested(x: Int) and Int tested(x: Int, y: Int), you don't know if they were DEFINED by overloading or by default values. But when put it as parameter, the former works while the latter doesn't.
This behaviour is also demonstrated by the snapshots attached.