Matching a parameter pack to a tuple of closures that utilizes it compiles, but is impossible to use.

[JessyCatterwaul]

Reproduction

Both forms compile without issue:

func mapWithoutTuple<each Input, each Output>(
  _ input: (repeat each Input),
  _ transform: repeat (each Input) -> each Output
) -> (repeat each Output) {
  (repeat (each transform)(each input))
}

func mapWithTuple<each Input, each Output>(
  _ input: (repeat each Input),
  _ transform: (repeat (each Input) -> each Output) // The difference is only these outer parentheses.
) -> (repeat each Output) {
  (repeat (each transform)(each input))
}

The first form is usable.

#expect(
  // Explicit "\Int.self" is required here. Maybe a different bug?
  mapWithoutTuple(0, \Int.self) as Int == 0
)
#expect(
  mapWithoutTuple((0, 1), \.self, \.self) == (0, 1)
)

The second form is not:

_ = mapWithTuple(0, \Int.self)
_ = mapWithTuple((0, 1), (\.self, \.self))

This results in various errors.

Expected behavior

While splatting would be ideal, where parameters being tuples, or not, didn't matter, we should at least be able to write overloads that use either form. And if a form compiles, it should be usable.

Environment

swift-driver version: 1.112.3 Apple Swift version 6.0 (swiftlang-6.0.0.6.8 clang-1600.0.23.1)
Target: arm64-apple-macosx14.0

Additional Information

This is not a problem with only one parameter pack.

func forEach<each Input, Error>(
  _ input: (repeat each Input),
  _ body: (repeat (each Input) throws(Error) -> Void)
) throws(Error) {
  repeat try (each body)(each input)
}

var value = 0
func add(_ summand: Int) { value += summand }
forEach((1, 2), (add, add))
#expect(value == 3) // ✅

[AnthonyLatsis]

Reduction:

func test<each I, each O>(
  _: (repeat each I),
  _: (repeat (each I) -> each O)
) {}

func f(_: Int) -> Int {}

test((0, 1), (f, f))

287 | func f(_: Int) -> Int {}
288 | 
289 | test((0, 1), (f, f))
    |              `- error: '((Int) -> Int, (Int) -> Int)' is not convertible to '(repeat (Int, Int) -> _, _)', tuples have a different number of elements [tuple_types_not_convertible_nelts]
290 | 
291 | 

Tested with 8493312.