Re: [PATCH v2 2/2] meson: prefer POSIX-specified shell path

From: Patrick Steinhardt <ps@pks.im>
Date: Apr 25, 2025, 11:52 UTC
Message-ID: <aAt3Yc1NVZxsvSVX@pks.im>
In-Reply-To: <aAtopiMkJpF2RdjG@tapette.crustytoothpaste.net>

On Fri, Apr 25, 2025 at 10:49:10AM +0000, brian m. carlson wrote:

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> On 2025-04-25 at 05:47:45, Patrick Steinhardt wrote:
> > Meson detects the path of the target shell via `find_program("sh")`,
> > which essentially does a lookup via `PATH`. This may easily lead to a
> > subtly-broken Git distribution when the build host has its shell in a
> > non-standard location that the target host doesn't know about.
> > 
> > Fix the issue by appending "/bin" to the custom program path, which
> > causes us to prefer "/bin/sh" over a `PATH` lookup. As this location is
> > specified by POSIX this should make us pick a better default shell path
> > on all POSIX-compliant systems.
> 
> Can you provide a citation for that?  I don't see that in the POSIX
> 1003.1-2024 directory structure document[0].  More specifically, I think
> there are some proprietary Unix systems where `/bin/sh` is the original
> Bourne shell and is not POSIX compliant and some other path is the
> POSIX-compliant `sh`.

Hrmpf, you're right. I feel like I relearn this piece of trivia every couple years. POSIX is quite specific here:

    Applications should note that the standard PATH to the shell cannot
    be assumed to be either /bin/sh or /usr/bin/sh, and should be
    determined by interrogation of the PATH returned by getconf PATH ,
    ensuring that the returned pathname is an absolute pathname and not
    a shell built-in.

Anyway, given the following...

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> I'll also point out that we require more than POSIX compliance in that
> we require `local`, so even if `/bin/sh` is POSIX compliant, that
> doesn't mean that it's suitable for Git.  `/bin/sh` meets our needs on
> all the Linux distros I'm aware of, plus the BSDs, but if it were AT&T
> ksh, that would not meet our needs since it doesn't support `local`,
> even though it's POSIX compliant.

... prefering "/bin/sh" is still the right thing to do as it tends to work on most systems supported by us, even though it's non-POSIX. But in any case, the commit message needs to be adjusted.

Thanks!

Patrick