Issue in rethrowing protocol

[twittemb]

Describe the bug
There might be an issue with the current implementation of rethrowing protocol conformance, that makes possible to throw an Error while the generic parameter is a non Throwing implementation.

Steps To Reproduce
Steps to reproduce the behavior:

Given a type that conforms to a rethrowing protocol such as this AsyncSequence:

struct AsyncDummySequence<Base: AsyncSequence>: AsyncSequence {
  typealias Element = Base.Element
  typealias AsyncIterator = Iterator

  let base: Base

  func makeAsyncIterator() -> AsyncIterator {
    Iterator(base: self.base.makeAsyncIterator())
  }

  struct Iterator: AsyncIteratorProtocol {
    var base: Base.AsyncIterator

    mutating func next() async rethrows -> Element? {
      try await withTaskCancellationHandler {
      } operation: {
        try Result<Element?, Error>.failure(NSError(domain: "", code: 1)).get(). // -> here the compiler does not complain about trying on a type that is not a generic parameter, because of the call being wrapped inside a rethrowing function.
      }
    }
}

we can use it with a non throwing generic AsyncSequence, not using try await although we clearly will throw an error in the next() function:

let nonThrowingSequence = AsyncStream<Int> { continuation in
  continuation.yield(1)
  continuation.finish()
}

let seq = AsyncDummySequence(base: nonThrowingSequence)

for await element in seq { // -> no need to use `try await` although the sequence will throw
  print(element)
}

When running that code, the iteration seems to be blocked.

Expected behavior
The compiler should complain about using try on a type that is not the generic parameter, just as it does with this code:

mutating func next() async rethrows -> Element? {
  try Result<Element, Error>.failure(NSError(domain: "", code: 1)).get() // -> does not compile
}

Environment (please fill out the following information)

• OS Monterey 12.5.1
• Xcode Version/Tag/Branch: Xcode 13.4.1 (13F100)
• Swift version 5.6.1 (swiftlang-5.6.0.323.66 clang-1316.0.20.12)
• MacBook Pro M1 ultra

Additional context
Forum link: Forum