[gnome-desktop] Fix the soname versioning for libgnome-desktop

[Emmanuele Bassi <ebassi src gnome org>]

commit 854cfe77cdc62206a619986a97391b59a2464a21
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Sat Sep 8 12:34:57 2018 +0100

    Fix the soname versioning for libgnome-desktop
    
    With Meson, using the `soversion` argument of a library() target means
    setting the explicit soname, e.g.:
    
        soversion: 17.0.2
    
    will be used to generate:
    
        libgnome-desktop-3.so.17.0.2
    
    Unlike libtool, though, Meson will not generate the symbolic links for
    the first component of the soversion:
    
        libgnome-desktop-3.so.17
    
    Which is what the dynamic linker will actually use to resolve the
    library dependency at link time.
    
    In order to get a symbolic link, we need to use the `version` field for
    the soname, and the `soversion` field for the first component:
    
        version: '17.0.2'
        soversion: '17'
    
    To avoid having to manually set two fields, we can generate the
    `soversion` value from the `version` one, so that they will always be in
    sync.
    
    This fixes the build of gnome-shell on Continuous, which has been
    failing since gnome-desktop has been moved to Meson with the error:
    
        ld: warning: libgnome-desktop-3.so.17, needed by /usr/lib/libmutter-3.so,
        not found (try using -rpath or -rpath-link)
    
    Signed-off-by: Emmanuele Bassi <ebassi gnome org>

 libgnome-desktop/meson.build | 1 +
 meson.build                  | 8 +++++---
 2 files changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/libgnome-desktop/meson.build b/libgnome-desktop/meson.build
index 4bc7bdb8..75bfee2a 100644
--- a/libgnome-desktop/meson.build
+++ b/libgnome-desktop/meson.build
@@ -85,6 +85,7 @@ libgnome_desktop = library('gnome-desktop-3',
   libgnome_desktop_sources,
   dependencies: [gnome_desktop_deps, m_dep, rt_dep, x_dep],
   soversion: soversion,
+  version: libversion,
   c_args: libargs,
   install: true
 )
diff --git a/meson.build b/meson.build
index 9b10bbf7..c30395e0 100644
--- a/meson.build
+++ b/meson.build
@@ -4,15 +4,17 @@ project('gnome-desktop', 'c',
   license: ['GPL2+', 'LGPL2+']
 )
 
-# Before making a release, the soversion string should be modified.
-# The string is of the form C.A.R.
+# Before making a release, the libversion string should be modified.
+# The string follows the libtool versioning scheme, and it is of the
+# form `C.A.R`.
 # - If interfaces have been changed or added, but binary compatibility has
 #   been preserved, change to C+1.A+1.0
 # - If binary compatibility has been broken (eg removed or changed interfaces)
 #   change to C+1.0.0
 # - If the interface is the same as the previous version, change to C.A.R+1
 
-soversion = '17.0.2'
+libversion = '17.0.2'
+soversion = libversion.split('.')[0]
 
 gdk_pixbuf_req = '>= 2.36.5'
 gtk_req = '>= 3.3.6'