Wrapping of long function signatures

[ahoppen]

Formatting this to 80 columns

func foo(someArgument: Int, andAnother: Int, andYetAnother: Int) -> Array<Substring> {
}

// produces

func foo(someArgument: Int, andAnother: Int, andYetAnother: Int) -> Array<
  Substring
> {}

Which is definitely not the most intuitive way of formatting it. I would have expected

func foo(
  someArgument: Int,
  andAnother: Int,
  andYetAnother: Int
) -> Array<Substring> {}

---

In a less extreme case, I would also expect the following to wrap the argument list instead of the return type

func foo(someArgument: Int, andAnother: Int, andYetAnother: Int, and: Int) -> Substring {}

// produces

func foo(someArgument: Int, andAnother: Int, andYetAnother: Int, and: Int)
  -> Substring
{}

func foo(someArgument: Int, andAnother: Int, andYet: Int, and: Int) -> Substring {}

// produces

func foo(someArgument: Int, andAnother: Int, andYet: Int, and: Int) -> Substring 
{}

[ahoppen]

Synced to Apple’s issue tracker as rdar://126967203

[allevato]

IIRC, the reason for this was that we wanted to allow tuple return values to break after the open paren, like:

func foo(someArgument: Int, andAnother: Int, andYetAnother: Int) -> (
  element: SomeType,
  element2: SomeOtherType
) {}

So we never grouped around the return type at all. We should probably use more knowledge of the return type's node kind here to determine whether we want to wrap it in a group or not.

---

In a less extreme case, I would also expect the following to wrap the argument list instead of the return type

This was the original behavior, which someone else at Apple (I think, it was years ago) argued was too aggressive. 🙂 It can be enabled by setting prioritizeKeepingFunctionOutputTogether in the configuration.

[ahoppen]

Oh, I didn’t know about prioritizeKeepingFunctionOutputTogether. Nice

[ahoppen]

Enabling prioritizeKeepingFunctionOutputTogether for the sourcekit-lsp codebase caused an assertion failure, I filed https://github.com/apple/swift-format/issues/726 for that.