On Fri, Nov 24, 2023 at 01:09:03PM -0500, Eric Sunshine wrote:

On Fri, Nov 24, 2023 at 6:37 AM Patrick Steinhardt [off-list ref] wrote:

quoted

We're manually parsing the HEAD reference in git-prompt to figure out
whether it is a symbolic or direct reference. This makes it intimately
tied to the on-disk format we use to store references and will stop
working once we gain additional reference backends in the Git project.

Refactor the code to always use git-symbolic-ref(1) to read HEAD, which
is both simpler and compatible with alternate reference backends.

This may get some push-back from Windows folks due to high
process-creation cost on that platform. As I recall, over the years, a
good deal of effort has been put into reducing the number of programs
run each time the prompt is displayed, precisely because invoking Git
(or other programs) multiple times became unbearably slow. In
particular, optimizations efforts have focussed on computing as much
as possible within the shell itself rather than invoking external
programs for the same purpose. Thus, this seems to be taking a step
backwards in that regard for the common or status quo case.

Would it be possible instead to, within shell, detect if the historic
file-based backend is being used in the current repository, thus
continue using the existing shell code for that case, and only employ
git-symbolic-ref if some other backend is in use?

Thanks for sharing my worries :)

I sent a patch a while ago to Han-Wen to make our Bash prompt script
work with the reftable backend without incurring the overhead of extra
subshells or processes when using the files based refs backend.  He
picked it up and used to include it in rerolls of the reftable patch
series; the last version of that patch is I believe at:

  https://public-inbox.org/git/patch-v4-21.28-443bdebfb5d-20210823T120208Z-avarab@gmail.com/