[gnome-photos] build: Avoid requiring Git for release tarballs

[Debarshi Ray <debarshir src gnome org>]

commit 45c499476dac4b52cb2355f3a74185a64bacff82
Author: Debarshi Ray <debarshir gnome org>
Date:   Sat Oct 13 14:23:21 2018 +0200

    build: Avoid requiring Git for release tarballs
    
    It's a tad nicer to not require Git when building release tarballs.
    While Git is definitely widely available, it's just one more thing
    that would have to be installed in the buildroots. Therefore, it is
    avoided for 'plain' builds.
    
    https://gitlab.gnome.org/GNOME/gnome-photos/merge_requests/71

 meson.build | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)
---
diff --git a/meson.build b/meson.build
index 3f6e1552..a0fdc369 100644
--- a/meson.build
+++ b/meson.build
@@ -30,10 +30,17 @@ po_dir = join_paths(source_root, 'po')
 
 top_inc = include_directories('.')
 
-git = find_program('git')
+photos_commit_id = ''
 if not photos_buildtype.contains('plain')
+  git = find_program('git')
+
   run_command(git, '-C', source_root, 'submodule', 'sync', '--recursive')
   run_command(git, '-C', source_root, 'submodule', 'update', '--init', '--recursive')
+
+  res = run_command(git, '-C', source_root, 'describe')
+  if res.returncode() == 0
+    photos_commit_id = res.stdout().strip()
+  endif
 endif
 
 cc = meson.get_compiler('c')
@@ -44,9 +51,8 @@ config_h.set_quoted('PACKAGE_TARNAME', meson.project_name())
 config_h.set_quoted('PACKAGE_URL', 'https://wiki.gnome.org/Apps/Photos')
 config_h.set_quoted('PACKAGE_VERSION', meson.project_version())
 
-res = run_command(git, '-C', source_root, 'describe')
-if res.returncode() == 0
-  config_h.set_quoted('PACKAGE_COMMIT_ID', res.stdout().strip())
+if photos_commit_id != ''
+  config_h.set_quoted('PACKAGE_COMMIT_ID', photos_commit_id)
 endif
 
 config_h.set_quoted('G_LOG_DOMAIN', meson.project_name())