[RFC] Freezing C++03 headers in libc++

[mordante]

Thanks a lot for your clarifications!

@philnik

@mordante

Some parts are not clear. For the bullet points can you add to which set of headers they belong. For example Start making simplifications to C++03 is this in the new “legacy” branch or in the existing “main” branch?

Thanks. I’ve update the bullets. This would be happening in the legacy branch. The changes would mostly be removing code that is not available in C++03 (e.g. all of ranges and format). I don’t think that should influence the maintenance burden in any way.

I’m not opposed to that. From the original description that was not clear to me.

@philnik

@mordante

I also like better clarification on what we’re going to backport. When the branches getting out of sync backporting will cause additional maintenance overhead, especially for non-trivial patches.

My expectation is that we’re only going to back-port libc++ bug fixes. No performance improvements or LWG issues. That would of course also apply to C++03 in the normal headers. Depending on the nature of the change we can also consider applying patches on the C++03 headers to avoid making the diff too large.

I would like to only do these changes when they are easy to backport. A bit of context I recently discovered <valarray> is quite broken. I’m looking at fixes. If backporting this to the “legacy” branch gets merge conflicts I really would like to omit them. The same if we uncover similar big issues. (I don’t expect them, but I didn’t expect <valarray> either.) So I prefer to promise this on a best effort basis and not unconditionally.

@philnik

To keep that burden as small as possible the proposal is to keep C++03 support in the main headers for that time and only refactor things when the C++03 headers are fully frozen.

+1 That point is not entirely clear in the timeline for me. However when we do this backporting should be a lot easier and I expect less of a maintenance burden.