waitForAllFix.swift

// ThrowingTaskGroup.waitForAll() behaviour was fixed in Swift 5.9
// This backports the Swift 5.9 behaviour to earlier versions
// https://github.com/apple/swift/pull/63016

public extension ThrowingTaskGroup {

  #if compiler(>=5.9)
  @available(*, deprecated, renamed: "waitForAll")
  #endif
  mutating func waitForAllFix() async throws {
    var firstError: Error? = nil

    // Make sure we loop until all child tasks have completed
    while !isEmpty {
      do {
        while let _ = try await next() {}
      } catch {
        // Upon error throws, capture the first one
        if firstError == nil {
          firstError = error
        }
      }
    }

    if let firstError {
      throw firstError
    }
  }
}

Test with the following. "Gone Fishing 🐠" will be printed every time.

try? await withThrowingTaskGroup(of: Void.self) { group in
  group.addTask { throw CancellationError() }
  group.addTask {
    try await Task.sleep(nanoseconds: 1_000_000_000)
    print("Gone Fishing 🐠")
  }

  try await group.waitForAllFix()
}