meson: populate project version via GIT-VERSION-GEN

The Git version for Meson is currently wired up manually. It can thus
grow (and already has grown) stale quite easily, as having multiple
sources of truth is never a good idea. This issue is mostly of cosmetic
nature as we don't use the project version anywhere, and instead use the
GIT-VERSION-GEN script to propagate the correct version into our build.
But it is somewhat puzzling when `meson setup` announces to build an old
Git release.

There are a couple of alternatives for how to solve this:

  - We can keep the version undefined, but this makes Meson output
    "undefined" for the version, as well.

  - We can use GIT-VERSION-GEN to generate the version for us. At the
    point of configuring the project we haven't yet figured out host
    details though, and thus we didn't yet set up the shell environment.
    While not an issue for Unix-based systems, this would be an issue in
    Windows, where the shell typically gets provided via Git for Windows
    and thus requires some special setup.

  - We can pull the default version out of GIT-VERSION-GEN and move it
    into its own file. This likely requires some adjustments for scripts
    that bump the version, but allows Meson to read the version from
    that file trivially.

Pick the second option and use GIT-VERSION-GEN as it gives us the most
accurate version. In order to fix the bootstrapping issue on Windows
systems we simply set the version to 'unknown' in case no shell was
found. As the version is only of cosmetic value this isn't really much
of an issue.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

meson.build

@@ -170,7 +170,14 @@
 
 project('git', 'c',
   meson_version: '>=0.61.0',
-  version: 'v2.47.GIT',
+  # The version is only of cosmetic nature, so if we cannot find a shell yet we
+  # simply don't set up a version at all. This may be the case for example on
+  # Windows systems, where we first have to bootstrap the host environment.
+  version: find_program('sh', required: false).found() ? run_command(
+    'GIT-VERSION-GEN', meson.current_source_dir(), '--format=@GIT_VERSION@',
+    capture: true,
+    check: true,
+  ).stdout().strip() : 'unknown',
 )
 
 fs = import('fs')