gettext: explicitly pass source root / subdir as cli args

Because this is a wrapper script and we could/should do this, we even
have half the infra for it.

mesonbuild/modules/i18n.py

@@ -251,6 +251,9 @@ class I18nModule(ExtensionModule):
         extra_arg = '--extra-args=' + '@@'.join(extra_args) if extra_args else None
 
         potargs = state.environment.get_build_command() + ['--internal', 'gettext', 'pot', pkg_arg]
+        potargs.append(f'--source-root={state.source_root}')
+        if state.subdir:
+            potargs.append(f'--subdir={state.subdir}')
         if datadirs:
             potargs.append(datadirs)
         if extra_arg:
@@ -292,6 +295,9 @@ class I18nModule(ExtensionModule):
         targets.append(allgmotarget)
 
         updatepoargs = state.environment.get_build_command() + ['--internal', 'gettext', 'update_po', pkg_arg]
+        updatepoargs.append(f'--source-root={state.source_root}')
+        if state.subdir:
+            updatepoargs.append(f'--subdir={state.subdir}')
         if lang_arg:
             updatepoargs.append(lang_arg)
         if datadirs:

mesonbuild/scripts/gettext.py

@@ -23,6 +23,7 @@ parser.add_argument('--pkgname', default='')
 parser.add_argument('--datadirs', default='')
 parser.add_argument('--langs', default='')
 parser.add_argument('--localedir', default='')
+parser.add_argument('--source-root', default='')
 parser.add_argument('--subdir', default='')
 parser.add_argument('--xgettext', default='xgettext')
 parser.add_argument('--msgmerge', default='msgmerge')
@@ -45,7 +46,7 @@ def read_linguas(src_sub: str) -> T.List[str]:
         print(f'Could not find file LINGUAS in {src_sub}')
         return []
 
-def run_potgen(src_sub: str, xgettext: str, pkgname: str, datadirs: str, args: T.List[str]) -> int:
+def run_potgen(src_sub: str, xgettext: str, pkgname: str, datadirs: str, args: T.List[str], source_root: str) -> int:
     listfile = os.path.join(src_sub, 'POTFILES.in')
     if not os.path.exists(listfile):
         listfile = os.path.join(src_sub, 'POTFILES')
@@ -59,7 +60,7 @@ def run_potgen(src_sub: str, xgettext: str, pkgname: str, datadirs: str, args: T
 
     ofile = os.path.join(src_sub, pkgname + '.pot')
     return subprocess.call([xgettext, '--package-name=' + pkgname, '-p', src_sub, '-f', listfile,
-                            '-D', os.environ['MESON_SOURCE_ROOT'], '-k_', '-o', ofile] + args,
+                            '-D', source_root, '-k_', '-o', ofile] + args,
                            env=child_env)
 
 def update_po(src_sub: str, msgmerge: str, msginit: str, pkgname: str, langs: T.List[str]) -> int:
@@ -77,18 +78,16 @@ def run(args: T.List[str]) -> int:
     subcmd = options.command
     langs = options.langs.split('@@') if options.langs else None
     extra_args = options.extra_args.split('@@') if options.extra_args else []
-    subdir = os.environ.get('MESON_SUBDIR', '')
-    if options.subdir:
-        subdir = options.subdir
-    src_sub = os.path.join(os.environ['MESON_SOURCE_ROOT'], subdir)
+    subdir = options.subdir
+    src_sub = os.path.join(options.source_root, subdir)
 
     if not langs:
         langs = read_linguas(src_sub)
 
     if subcmd == 'pot':
-        return run_potgen(src_sub, options.xgettext, options.pkgname, options.datadirs, extra_args)
+        return run_potgen(src_sub, options.xgettext, options.pkgname, options.datadirs, extra_args, options.source_root)
     elif subcmd == 'update_po':
-        if run_potgen(src_sub, options.xgettext, options.pkgname, options.datadirs, extra_args) != 0:
+        if run_potgen(src_sub, options.xgettext, options.pkgname, options.datadirs, extra_args, options.source_root) != 0:
             return 1
         return update_po(src_sub, options.msgmerge, options.msginit, options.pkgname, langs)
     else: