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Bad error messaging when opening multiple existentials #59691

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mbrandonw opened this issue Jun 24, 2022 · 1 comment

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bug

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mbrandonw commented Jun 24, 2022 •

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Describe the bug

The following code is invalid because the two opened existentials may have different types, but the error message does not explain that well:

func equals(_ lhs: Any, _ rhs: Any) -> Bool? {
  func open<A: Equatable>(_ lhs: A, _ rhs: A) -> Bool {
    lhs == rhs
  }

  guard
    let lhs = lhs as? any Equatable,
    let rhs = rhs as? any Equatable
  else { return nil }


  return open(lhs, rhs)
}

🛑 Type 'any Equatable' cannot conform to 'Equatable'

Expected behavior
A better error message that lets the user know it's not possible to open multiple existentials.

Environment

OS: 12.4 (21F79)
Xcode Version/Tag/Branch: Version 14.0 beta 2 (14A5229c)

mbrandonw added the bug label

slavapestov assigned hborla

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hborla commented Jun 28, 2022

Great idea for a tailored error message, thanks!

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