Incorrectly removing empty trailing closure parentheses in a curried call

[a7medev]

Problem

When calling swift-format on the following code

func perform() -> (() -> Void) -> Void {
  return { body in
    body()
  }
}

perform()() {
  print("Hello world")
}

It produces the following code (notice the () removed at the perform call)

func perform() -> (() -> Void) -> Void {
  return { body in
    body()
  }
}

perform() {
  print("hi")
}

This code doesn't compile and produces the following diagnostic.

File.swift:7:11: error: extra trailing closure passed in call
 5 | }
 6 | 
 7 | perform() {
   |           `- error: extra trailing closure passed in call
 8 |   print("Hello world")
 9 | }

The above example is also easily reproducible with implicitly-curried instance methods as in the following example.

struct Executor {
  func execute(body: () throws -> Void) rethrows {
    body()
  }
}

let executor = Executor()

Executor.execute(executor)() { }

Proposed Solution

swift-format should only remove empty function arguments () before a trailing closure when the FunctionCallExpr's callee is not a FunctionCallExpr nor a SubscriptCallExpr to avoid incorrectly associating the trailing closure with the callee.