meson: improve comment and fix deprecated functions

- Clarify that 'mm-glib' dep is for ModemManager (not Network
   Manager which is below). The comment also helps people
   which may confuse it with glibmm library.

 - Fix following Meson warning about two deprecated functions:
   WARNING: Deprecated features used:
   * 0.56.0: {'dependency.get_pkgconfig_variable', 'meson.source_root'}

meson.build

@@ -238,8 +238,9 @@ config_h.set('HAVE_MALCONTENT', enable_malcontent,
              description: 'Define to 1 if malcontent support is enabled')
 
 if host_is_linux
-  # network manager
+  # ModemManager
   mm_dep =  dependency('mm-glib', version: '>= 0.7')
+  # NetworkManager
   network_manager_deps = [
     dependency('libnm', version: '>= 1.24.0'),
     dependency('libnma-gtk4', version: '>= 1.10.2'),
@@ -285,8 +286,8 @@ gnome = import('gnome')
 i18n = import('i18n')
 pkg = import('pkgconfig')
 
-po_dir = join_paths(meson.source_root(), 'po')
-its_dir = join_paths(meson.source_root(), 'gettext')
+po_dir = join_paths(meson.project_source_root(), 'po')
+its_dir = join_paths(meson.project_source_root(), 'gettext')
 
 install_subdir(
   'gettext',

panels/background/meson.build

@@ -19,7 +19,7 @@ common_sources = []
 
 enums = 'gdesktop-enums-types'
 enums_header = files(
-  gsettings_desktop_dep.get_pkgconfig_variable('prefix') + '/include/gsettings-desktop-schemas/gdesktop-enums.h',
+  gsettings_desktop_dep.get_variable(pkgconfig: 'prefix') + '/include/gsettings-desktop-schemas/gdesktop-enums.h',
   'cc-background-item.h'
 )
 

panels/datetime/meson.build

@@ -45,7 +45,7 @@ sources = files(
 
 enums = 'gdesktop-enums-types'
 enums_header = files(
-  gsettings_desktop_dep.get_pkgconfig_variable('prefix') + '/include/gsettings-desktop-schemas/gdesktop-enums.h',
+  gsettings_desktop_dep.get_variable(pkgconfig: 'prefix') + '/include/gsettings-desktop-schemas/gdesktop-enums.h',
   'cc-datetime-panel.h'
 )
 

tests/datetime/meson.build

@@ -14,7 +14,7 @@ env = [
 ]
 cflags = [
   '-DTEST_SRCDIR="@0@"'.format(meson.current_source_dir()),
-  '-DSRCDIR="@0@"'.format(meson.source_root() + '/panels/datetime')
+  '-DSRCDIR="@0@"'.format(meson.project_source_root() + '/panels/datetime')
 ]
 
 foreach unit: test_units

tests/network/meson.build

@@ -5,7 +5,7 @@ cflags = [
   '-DTEST_SRCDIR="@0@"'.format(meson.current_source_dir()),
   '-DNETWORKMANAGER_COMPILATION=NM_NETWORKMANAGER_COMPILATION_WITH_GLIB',
   '-DNETWORKMANAGER_COMPILATION_TEST',
-  '-DTEST_NM_SERVICE="@0@"'.format(join_paths(meson.source_root(), 'tests', 'network', 'nm-utils', 'test-networkmanager-service.py')),
+  '-DTEST_NM_SERVICE="@0@"'.format(join_paths(meson.project_source_root(), 'tests', 'network', 'nm-utils', 'test-networkmanager-service.py')),
 ]
 
 exe = executable(