[SE-0365] Allow implicit self in inner functions in [weak self] closures, like with [self] closures

[calda]

This PR fixes an issue in the implementation of SE-0365, where implicit self was disallowed inside inner function declarations:

doWorkEscaping { [weak self] in
  guard let self else { return }
  func innerFunction() {
    // Before: Error: call to method 'test' in closure requires explicit use of 'self' to make capture semantics explicit
    // Now allowed without an error
    test()
  }
}

The intent of SE-0365 is to mirror the behavior of SE-0269 with [self] captures. This usage is allowed by SE-0269, so it should be allowed by SE-0365 as well:

doWorkEscaping { [self] in
  func innerFunction() {
    test() // ✅
  }
}

I confirmed on the forums that this was an intentional design choice of SE-0269.

Please review: @xedin

[xedin]

Thank you! I left a few comments inline, I would be great to get a few cases with more nesting and i.e. inits and subscripts involved (both valid and invalid)

[calda]

Thanks for the review @xedin -- I incorporated your suggestions and added more extensive tests in 6670639

[xedin]

Thank you!

[xedin]

@swift-ci please test

[xedin]

@swift-ci please test source compatibility

[calda]

The one issue in the Release source compat suite is unrelated:

build. MovieSwift, 5.0, 237010, MovieSwift, generic/platform=iOS
This project built successfully, but it was expected to fail. #65203