swiftFormat incorrectly removes parentheses

[Ahbee]

Im using the Xcode source editor extension with the default options,
however swiftFormat removes parentheses which makes the math incorrect

here is my input (I leave no space between b and + to show the bug)

import Foundation

func test() -> Double {
  let a = 2.0
  let b = 3.0
  let c = a * (b+ a)
  return c
}

here is the output, notice that parentheses are gone and the function produces different results

import Foundation

func test() -> Double {
  let a = 2.0
  let b = 3.0
  let c = a * b+ a
  return c
}

a lot of times I copy and paste equations from other sources like Matlab and Python. I run swift format immediately after the paste just to clean it up a little. Then I will fix any compile issues. This bug affects my workflow since I don't expect the formatting to change math like that.

[nicklockwood]

Writing b+ a is not permitted in Swift anyway because whitespace around operators is meaningful, so b+ would refer to a postfix unary + operator not the infix + operator.

I'm rather surprised that your (pre-SwiftFormat) example compiles ok, but perhaps Swift just treats it as a warning instead of an error?

I might be able to handle this as a special case, but the workaround for now would be to balance the spaces around the + (either a+b or a + b should work fine)

[nicklockwood]

Ah, sorry I should have read your comment more closely - you aren't saying that it did compile, but that you were running SwiftFormat as a pre-compile step.

TBH I think this is a bad idea. SwiftFormat is designed to function only with valid code. If the code is malformed then the behavior of SwiftFormat is undefined.

I might be able to handle this particular case because it's possible to infer the intent from the context, but in general I can't guarantee SwiftFormat won't mangle code that isn't valid Swift to begin with

[Ahbee]

hmm ok I understand about the valid code thing,
but even fixing the particular case of "postfix unary operators" would be good, I am sure its a common mistake for people to write a+ b instead of a+b

On a more general note I don't think SwiftFormat should remove parentheses if the math is undefined