Revert "meson: use vcs_tag() instead of custom script"

This reverts commit e4edf9203b.

Meson is unfortunately not quite ready yet, and prints stderr noise when
_not_ building from a git clone.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37717>

.gitlab-ci.yml

@@ -290,6 +290,7 @@ include:
     - if: *is-merge-attempt
       changes: &all_paths
         - VERSION
+        - bin/git_sha1_gen.py
         - bin/install_megadrivers.py
         - bin/symbols-check.py
         - bin/ci/**/*

bin/git_sha1_gen.py

@@ -0,0 +1,50 @@
+"""
+Generate the contents of the git_sha1.h file.
+"""
+
+import argparse
+import os
+import os.path
+import subprocess
+import sys
+
+
+def get_git_sha1():
+    """Try to get the git SHA1 with git rev-parse."""
+    git_dir = os.path.join(os.path.dirname(sys.argv[0]), '..', '.git')
+    try:
+        git_sha1 = subprocess.check_output([
+            'git',
+            '--git-dir=' + git_dir,
+            'rev-parse',
+            'HEAD',
+        ], stderr=open(os.devnull, 'w')).decode("ascii")
+    except Exception:
+        # don't print anything if it fails
+        git_sha1 = ''
+    return git_sha1
+
+
+def write_if_different(contents):
+    """
+    Avoid touching the output file if it doesn't need modifications
+    Useful to avoid triggering rebuilds when nothing has changed.
+    """
+    if os.path.isfile(args.output):
+        with open(args.output, 'r') as file:
+            if file.read() == contents:
+                return
+    with open(args.output, 'w') as file:
+        file.write(contents)
+
+
+parser = argparse.ArgumentParser()
+parser.add_argument('--output', help='File to write the #define in',
+                    required=True)
+args = parser.parse_args()
+
+git_sha1 = os.environ.get('MESA_GIT_SHA1_OVERRIDE', get_git_sha1())[:10]
+if git_sha1:
+    write_if_different('#define MESA_GIT_SHA1 " (git-' + git_sha1 + ')"')
+else:
+    write_if_different('#define MESA_GIT_SHA1 ""')

bin/meson.build

@@ -1,6 +1,7 @@
 # Copyright © 2017 Eric Engestrom
 # SPDX-License-Identifier: MIT
 
+git_sha1_gen_py = files('git_sha1_gen.py')
 gen_vs_module_defs_py = files('gen_vs_module_defs.py')
 gen_vs_module_defs_normal_command = [
   prog_python, gen_vs_module_defs_py,

src/git_sha1.h.in

@@ -1 +0,0 @@
-#define MESA_GIT_SHA1 @VCS_TAG@

src/meson.build

@@ -33,11 +33,12 @@ glsl_util_files = files(
     'mesa/program/dummy_errors.c',
 )
 
-sha1_h = vcs_tag(
-  input : 'git_sha1.h.in',
+sha1_h = custom_target(
+  'git_sha1.h',
   output : 'git_sha1.h',
-  command : ['git', 'show', '--no-patch', '--abbrev=10', '--format=" (git-%h)"'],
-  fallback : '""',
+  command : [prog_python, git_sha1_gen_py, '--output', '@OUTPUT@'],
+  build_by_default : true,
+  build_always_stale : true, # commit sha1 can change without having touched these files
 )
 
 if cc.get_argument_syntax() == 'msvc'