[PATCH v3 0/2] meson: prefer '/bin/sh' over PATH lookup

Hi,

at GitLab, we recently got a couple of bug reports about Git not being able to find its shell anymore. The root cause is that with Meson we have started to look up the shell via PATH, which may exist on the build host, but not on the target host. We have worked around this issue with a cross file:

    $ cat >cross.ini <<-EOF
    [binaries]
    sh = '/bin/sh'
    EOF
    $ meson setup build --cross-file=./cross.ini

But this made me remember the report from Peter [1] that Debian also faced this issue. So I decided to address the issue in Meson directly by preferring `/bin/sh` over a PATH-based lookup.

Changes in v2:
  - Simplify how we generate the summary.
  - Add a comment to explain ordering of the program path.
  - Link to v1: https://lore.kernel.org/r/20250424-pks-meson-posix-shell-v1-0-45e06ee4b6ad@pks.im

Changes in v3:
  - Stop claiming that "/bin/sh" is a POSIX-compliant path.
  - Link to v2: https://lore.kernel.org/r/20250425-pks-meson-posix-shell-v2-0-fddc6123511b@pks.im

Thanks!

Patrick

[1]: <20250209133027.64a865aa@gmx.net>

---
Patrick Steinhardt (2):
      meson: report detected runtime executable paths
      meson: prefer shell at "/bin/sh"

 meson.build | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

Range-diff versus v2:

1:  e749055ac00 = 1:  750aa492d76 meson: report detected runtime executable paths
2:  159a05d3533 ! 2:  d6417ba5ff6 meson: prefer POSIX-specified shell path
    @@ Metadata
     Author: Patrick Steinhardt <ps@pks.im>
     
      ## Commit message ##
    -    meson: prefer POSIX-specified shell path
    +    meson: prefer shell at "/bin/sh"
     
         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.
    +    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.
    +    causes us to prefer "/bin/sh" over a `PATH`-based lookup. While
    +    "/bin/sh" isn't standardized, this path tends to work alright on Linux
    +    and BSD distributions. Furthermore, "/bin/sh" is also the path we pick
    +    in our Makefile by default, which further demonstrates that this shell
    +    fulfills our needs.
     
         Note that we intentionally append, not prepend, to the custom program
         path. This is because the program path can be configured by the user via
    @@ meson.build: sed = find_program('sed', dirs: program_path, native: true)
      
     -target_shell = find_program('sh', dirs: program_path, native: false)
     +# Detect the target shell that is used by Git at runtime. Note that we prefer
    -+# '/bin/sh' over a PATH-based lookup given that '/bin/sh' is the location
    -+# specified by POSIX. This lookup can be overridden via `program_path`.
    ++# "/bin/sh" over a PATH-based lookup, which provides a working shell on most
    ++# supported systems. This path is also the default shell path used by our
    ++# Makefile. This lookup can be overridden via `program_path`.
     +target_shell = find_program('sh', dirs: program_path + [ '/bin' ], native: false)
      
      # Sanity-check that programs required for the build exist.

--- base-commit: a2955b34f48265d240ab8c7deb0a929ec2d65fd0 change-id: 20250424-pks-meson-posix-shell-4969161025c5