`meson dist` crashes with `git -C /sourcedir update-index` failing read-only file system

[martinpitt]

Describe the bug

My project runs tests in containers, which get the original source directory bind-mounted as a volume into the container's /source.

With Debian testing moving from meson 1.4.1 to 1.5.0, running the build now fails reliably in GitHub actions:

+ meson dist --no-test --allow-dirty
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/mesonbuild/mesonmain.py", line 188, in run
    return options.run_func(options)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/mesonbuild/mdist.py", line 371, in run
    names = project.create_dist(archives)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/mesonbuild/mdist.py", line 200, in create_dist
    self.process_git_project(self.src_root, self.distdir)
  File "/usr/lib/python3/dist-packages/mesonbuild/mdist.py", line 161, in process_git_project
    if self.have_dirty_index():
       ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/mesonbuild/mdist.py", line 143, in have_dirty_index
    subprocess.check_call(['git', '-C', self.src_root, 'update-index', '-q', '--refresh'])
  File "/usr/lib/python3.12/subprocess.py", line 413, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['git', '-C', '/source', 'update-index', '-q', '--refresh']' returned non-zero exit status 128.

ERROR: Unhandled python exception

    This is a Meson bug and should be reported!

To Reproduce

I'm a bit confused by this. I can replicate this 100% in a "full" debug build with

git clone https://github.com/martinpitt/umockdev
cd umockdev
DEBUG=1 tests/run-apt docker.io/amd64/debian:testing

That fails. Enter the container with

podman start -l
podman exec -itl bash
su -s /bin/bash - build
cd /tmp/dbg
meson dist --no-test --allow-dirty

That reproduces it as well. I can also directly run the git command which explains the reason:

build@15f92f2cd7a5:/tmp/dbg$ git -C /source/ update-index --refresh
fatal: Unable to create '/source/.git/index.lock': Read-only file system

Yes, that's intended -- I do not want tests or anything in the build dir to change the source tree or git status.

However, about 3 minutes later running the exact same git or meson command started to succeed.

It should be possible to reproduce it in a stripped down version of the container invocation:

podman run -it --rm -v .:/source docker.io/amd64/debian:testing sh -exc 'apt update; apt install -y meson git valac libudev-dev libpcap-dev; meson setup /tmp/build /source; meson dist -C /tmp/build --no-test --allow-dirty'

but that works.

There seems to be something weird going on with git in the background, which sometimes seems to access the source directory in a writable manner.

That update-index command is apparently new -- can it be adjusted to tolerate failure, or not be done on read-only source dirs?

system parameters

• Is this a cross build or just a plain native build (for the same computer)?: no
• what operating system (e.g. MacOS Catalina, Windows 10, CentOS 8.0, Ubuntu 18.04, etc.): Debian testing
• what Python version are you using: 3.12.4
• what meson --version: 1.5.0
• what ninja --version if it's a Ninja build: 1.12.1

[eli-schwartz]

That update-index command is apparently new -- can it be adjusted to tolerate failure, or not be done on read-only source dirs?

Yes -- there's no reason we should care about its return value at all. The sole purpose of it is to make the next command more likely to return correct information. See above ^^

[martinpitt]

Thanks @eli-schwartz for the super-fast fix! 🌟