[gnome-shell] build: Automatically bump mutter API version each cycle

[Florian Müllner <fmuellner src gnome org>]

commit 466dc8da8fa7243322fd12c8165f5a7f9d1eff29
Author: Florian Müllner <fmuellner gnome org>
Date:   Tue Jul 23 22:34:58 2019 +0200

    build: Automatically bump mutter API version each cycle
    
    Mutter will now bump the API version automatically at the
    beginning of a new development cycle; do the same here.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/641

 meson.build | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 42c7f02d9..307cd6be6 100644
--- a/meson.build
+++ b/meson.build
@@ -4,9 +4,14 @@ project('gnome-shell', 'c',
   license: 'GPLv2+'
 )
 
+split_version = meson.project_version().split('.')
+
 # We depend on a specific version of the libmutter API. The mutter variants of
 # the Cogl and Clutter libraries also use this API version.
-mutter_api_version = '4'
+# The API version is increased automatically each development cycle,
+# starting with 0 in 3.23.x
+api_version = (split_version[1].to_int() - 23) / 2
+mutter_api_version = '@0@'.format(api_version)
 
 clutter_pc = 'mutter-clutter-' + mutter_api_version
 cogl_pc = 'mutter-cogl-' + mutter_api_version