extensionUtils: Add gettext convenience helpers

We have initTranslations() for binding an extension's
gettext domain, but nothing to help with using gettext
from an extension.

Such help would be useful though, as an extension that
calls textdomain() like a normal application would
inadvertently changes the default domain for the whole
gnome-shell process.

Instead, extensions have to use domain-specific versions
of the gettext functions:

```js
const Gettext = imports.gettext.domain('my-extension');
const _ = Gettext.gettext;
```

Make this a bit easier by adding those functions directly
to the extensions object when initTranslations() is called,
then expose helper functions for calling them.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2594

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1941>

js/misc/extensionUtils.js

@@ -1,7 +1,8 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 /* exported ExtensionState, ExtensionType, getCurrentExtension,
-   getSettings, initTranslations, openPrefs, isOutOfDate,
-   installImporter, serializeExtension, deserializeExtension */
+   getSettings, initTranslations, gettext, ngettext, pgettext,
+   openPrefs, isOutOfDate, installImporter, serializeExtension,
+   deserializeExtension */
 
 // Common utils for the extension system and the extension
 // preferences tool
@@ -112,6 +113,64 @@ function initTranslations(domain) {
         Gettext.bindtextdomain(domain, localeDir.get_path());
     else
         Gettext.bindtextdomain(domain, Config.LOCALEDIR);
+
+    Object.assign(extension, Gettext.domain(domain));
+}
+
+/**
+ * gettext:
+ * @param {string} str - the string to translate
+ *
+ * Translate @str using the extension's gettext domain
+ *
+ * @returns {string} - the translated string
+ *
+ */
+function gettext(str) {
+    return callExtensionGettextFunc('gettext', str);
+}
+
+/**
+ * ngettext:
+ * @param {string} str - the string to translate
+ * @param {string} strPlural - the plural form of the string
+ * @param {number} n - the quantity for which translation is needed
+ *
+ * Translate @str and choose plural form using the extension's
+ * gettext domain
+ *
+ * @returns {string} - the translated string
+ *
+ */
+function ngettext(str, strPlural, n) {
+    return callExtensionGettextFunc('ngettext', str, strPlural, n);
+}
+
+/**
+ * pgettext:
+ * @param {string} context - context to disambiguate @str
+ * @param {string} str - the string to translate
+ *
+ * Translate @str in the context of @context using the extension's
+ * gettext domain
+ *
+ * @returns {string} - the translated string
+ *
+ */
+function pgettext(context, str) {
+    return callExtensionGettextFunc('pgettext', context, str);
+}
+
+function callExtensionGettextFunc(func, ...args) {
+    const extension = getCurrentExtension();
+
+    if (!extension)
+        throw new Error(`${func}() can only be called from extensions`);
+
+    if (!extension[func])
+        throw new Error(`${func}() is used without calling initTranslations() first`);
+
+    return extension[func](...args);
 }
 
 /**

lint/eslintrc-shell.yml

@@ -18,6 +18,7 @@ overrides:
   - files: js/**
     excludedFiles:
       - js/portalHelper/*
+      - js/misc/extensionUtils.js
     globals:
       global: readonly
       _: readonly

subprojects/extensions-tool/src/templates/indicator/extension.js

@@ -22,14 +22,13 @@ const GETTEXT_DOMAIN = 'my-indicator-extension';
 
 const { GObject, St } = imports.gi;
 
-const Gettext = imports.gettext.domain(GETTEXT_DOMAIN);
-const _ = Gettext.gettext;
-
 const ExtensionUtils = imports.misc.extensionUtils;
 const Main = imports.ui.main;
 const PanelMenu = imports.ui.panelMenu;
 const PopupMenu = imports.ui.popupMenu;
 
+const _ = ExtensionUtils.gettext;
+
 const Indicator = GObject.registerClass(
 class Indicator extends PanelMenu.Button {
     _init() {