capnp: compile with C++20 standard level

[dblsaiko]

capnp silently doesn't compile parts of the code when compiled with the default standard level.

• Have you followed the guidelines for contributing?
• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

---

[github-actions]

Thanks for contributing to Homebrew! 🎉 It looks like you're having trouble with a CI failure. See our contribution guide for help. You may be most interested in the section on dealing with CI failures. You can find the CI logs in the Checks tab of your pull request.

[botantony]

Any reasons why this change is needed?

[dblsaiko]

Building a project (Lix package manager) that uses kj coroutines without this change fails with linker errors because the coroutine classes aren't compiled.

https://github.com/capnproto/capnproto/blob/release-1.1.0/c%2B%2B/src/kj/async-prelude.h#L36-L40

[daeho-ro]

Why not just change the CMakeList file?

[dblsaiko]

Is that easier to patch than just adding arguments to CMake? I don't think I understand what you mean.

[daeho-ro]

If this is crucial, then the changes go to upstream and apply the original file. But you did it from homebrew and so I ask a question 😅

[dblsaiko]

Upstream now already requires corouties and fails the build otherwise instead of not compiling the classes, it's just not in a release yet: capnproto/capnproto@3cbd744

[chenrui333]

Upstream now already requires corouties and fails the build otherwise instead of not compiling the classes, it's just not in a release yet: capnproto/capnproto@3cbd744

then maybe add a code comment to remove it in the next release? otherwise should be good to go.

[github-actions]

@daeho-ro has requested bottles to be published to this PR.

Please do not push to this PR branch before the bottle commits have been pushed, as this results in a state that is difficult to recover from. If you need to resolve a merge conflict, please use a merge commit. Do not force-push to this PR branch.