build/meson: fix location of introspection files

With glib < 2.51.3, gdbus-codegen does not understand "--output-directory" [1].
Hence, the generated files are like

    "build/dbus-org.freedesktop.NetworkManager.Device.WifiP2P.xml"

instead of

    "build/introspection/dbus-org.freedesktop.NetworkManager.Device.WifiP2P.xml"

But gnome.gdbus_codegen() returns a path as if it would be inside
"build/introspection". Hack around that, by patching the correct path
otherwise. This is still ugly, because repeated "ninja -C build" calls
will always try to rebuild this target (because the wrong file name
is considered).

See also [2].

[1] ee09bb704f
[2] 2e93ed58c3/mesonbuild/modules/gnome.py (L1170)

(cherry picked from commit ad9e5995e1)

docs/api/meson.build

@@ -23,11 +23,11 @@ configure_file(
 content_files += join_paths(meson.source_root(), 'COPYING')
 filecopier = find_program('cp')
 foreach intro : introspection_files
-  path = intro.full_path().split('/')[-1]
+  path = intro[1].split('/')[-1]
   custom_target(path,
-                input: intro,
+                input: intro[0],
                 output: path,
-                command : [filecopier, '@INPUT@', '@OUTPUT@'],
+                command: [filecopier, intro[1], '@OUTPUT@'],
                 build_by_default: true,
   )
 endforeach

introspection/meson.build

@@ -73,13 +73,20 @@ foreach iface: ifaces
 
   sources += res
 
-  content_files += join_paths(meson.current_build_dir(), 'dbus-' + iface_xml)
+  if gio_unix_dep.version().version_compare('>= 2.51.3')
+    dbus_iface_xml_path = join_paths(meson.current_build_dir(), 'dbus-' + iface_xml)
+  else
+    dbus_iface_xml_path = join_paths(meson.build_root(), 'dbus-' + iface_xml)
+  endif
+
+  content_files += dbus_iface_xml_path
 
   # res is an array only since 0.46. Documentation won't work with
   # older versions
   if meson.version().version_compare('>= 0.46.0')
-    introspection_files += res[2]
+    introspection_files += [ [res[2], dbus_iface_xml_path] ]
   endif
+
 endforeach
 
 install_data(