Re: autoconf's AC_PROG_GNU_M4 macro (from m4.m4) and the --gnu flag to gm4

On Sun, Jul 21, 2024, at 12:40 AM, Eric Gallager wrote:
> Hi, I'm writing because I will occasionally see messages like the
> following from CI systems (specifically GitHub Actions' macOS runners)
> when they attempt to run autoconf:
>
> /Applications/Xcode_15.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/gm4:
> unrecognized option `--gnu'
> Try 
> `/Applications/Xcode_15.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/gm4
> --help' for more information.
> autom4te: error: gm4 failed with exit status: 1
>
> My first attempt at fixing this was hacking in support for the `--gnu`
> flag for Apple's copy of gm4, but since the apple-oss-distributions
> organization has pull requests turned off, there isn't much I can
> really do there to get Apple to upstream it:
> https://github.com/apple-oss-distributions/gm4/compare/main...cooljeanius:apple-gm4:gnu_flag

Yeah, don't bother.  Their copy of GNU M4 is too old for us _anyway_.
They ought to either get over their GPLv3 phobia or stop shipping GNU
utilities at all.

> I think what is happening here is that
> [g]m4's support for the `--gnu` flag gets detected at autoconf's
> configure time, but then when the user overrides the M4 variable to
> point to a different [g]m4, the M4_GNU variable stays set to whatever
> it was first detected as, which might not match up with what the new
> [g]m4 supports. I'm wondering if there's some way that autoconf could
> shift around the timing of these checks so that it doesn't try passing
> `--gnu` to an installation of [g]m4 that doesn't support it?

It probably _would_ make more sense to do that check at runtime, in
autom4te.  I'll think about how to make that happen.

zw