bug#65908: 29.1.50; Emacs 29 regresses on macOS

[Alan Third <alan@idiocy.org>]

On Wed, Oct 04, 2023 at 02:43:05PM +0200, Gerd Möllmann wrote:
> Gerd Möllmann <gerd.moellmann@gmail.com> writes:
> 
> > Stefan Kangas <stefankangas@gmail.com> writes:
> >
> >>> I try to update the list of failing commits monthly.
> >>
> >> Thanks for maintaining that script.  We need more people showing that
> >> kind of initiative and drive.
> >
> > +1
> >
> > And, three weeks later, the culprit is
> >
> > commit 058c012f73d4abe014ace44b46c23babd48aebbc (HEAD)
> > Author: Alan Third <alan@idiocy.org>
> > Date:   Sun Nov 14 15:09:43 2021 +0000
> >
> >     Only set LANG if the ID is valid
> >     
> >     * src/nsterm.m (ns_init_locale): Check the provided locale identifier
> >     is available before trying to use it.
> >
> > But don't ask me how that comes into play here because that function
> > seems to be called from main only.  Maybe it's because LANG is now not
> > always set, but used somewhere else?

AFAIK LANG isn't used by Emacs at all. That code is just there to help
set up a default environment for running shell commands.

> As an experiment, I evaluated this in *scratch*:
> 
> (setenv "LANG" "")
> (setenv "LC_COLLATE" "C")
> (setenv "LC_CTYPE" "UTF-8")
> (setenv "LC_MESSAGES" "C")
> (setenv "LC_MONETARY" "C")
> (setenv "LC_NUMERIC" "C")
> (setenv "LC_TIME" "C")
> 
> which is the output of 'locale' in a terminal, translated to Elisp.
> With these settings, the slowdown is gone, without changing the code.

So is Emacs run in the terminal with a LANG of something like
en_GB.UTF-8 slower too? Because iirc my mac's terminal doesn't default
to 'C' and I don't see anything GUI specific in the test code...

FWIW I don't see any meaningful difference using different locale
settings on my Debian box, which makes me wonder if there is some
low-level darwin code that reads the locale from the environment. Any
idea if it's loading the files or stepping through the defuns that's
slower, or both?

Long story short: I have no idea what's going on here.
-- 
Alan Third