Bug 1835163 - Look up pivot languages for language detection; r=nordzilla

Depends on D179485

Differential Revision: https://phabricator.services.mozilla.com/D179486

toolkit/components/translations/actors/TranslationsChild.sys.mjs

@@ -43,6 +43,8 @@ const DOC_LANGUAGE_DETECTION_THRESHOLD = 0.65;
  */
 const DOC_TEXT_TO_IDENTIFY_LENGTH = 1024;
 
+const PIVOT_LANGUAGE = "en";
+
 import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
 
 ChromeUtils.defineESModuleGetters(lazy, {
@@ -677,22 +679,42 @@ export class TranslationsChild extends JSWindowActorChild {
         break;
       }
 
+      if (!langTags.isDocLangTagSupported) {
+        if (languagePairs.some(({ toLang }) => toLang === preferredLangTag)) {
+          // Only match the "to" language, since the "from" is not supported.
+          langTags.userLangTag = preferredLangTag;
+        }
+        break;
+      }
+
+      // Is there a direct language pair match?
       if (
-        languagePairs.some(({ fromLang, toLang }) => {
-          if (langTags.isDocLangTagSupported) {
-            // Match both from and to languages.
-            return (
-              fromLang === langTags.docLangTag && toLang === preferredLangTag
-            );
-          }
-          // Only match the to language, since the "from" is not supported.
-          return toLang === preferredLangTag;
-        })
+        languagePairs.some(
+          ({ fromLang, toLang }) =>
+            fromLang === langTags.docLangTag && toLang === preferredLangTag
+        )
       ) {
         // A match was found in one of the preferred languages.
         langTags.userLangTag = preferredLangTag;
         break;
       }
+
+      // Is there a pivot language match?
+      if (
+        // Match doc -> pivot
+        languagePairs.some(
+          ({ fromLang, toLang }) =>
+            fromLang === langTags.docLangTag && toLang === PIVOT_LANGUAGE
+        ) &&
+        // Match pivot -> preferred language
+        languagePairs.some(
+          ({ fromLang, toLang }) =>
+            fromLang === PIVOT_LANGUAGE && toLang === preferredLangTag
+        )
+      ) {
+        langTags.userLangTag = preferredLangTag;
+        break;
+      }
     }
 
     if (!langTags.userLangTag) {

toolkit/components/translations/tests/browser/browser.ini

@@ -19,3 +19,4 @@ skip-if =
 [browser_translation_document.js]
 [browser_translations_actor.js]
 [browser_translations_actor_preferred_language.js]
+[browser_translations_lang_tags.js]

toolkit/components/translations/tests/browser/browser_translations_lang_tags.js

+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const PIVOT_LANGUAGE = "en";
+
+const LANGUAGE_PAIRS = [
+  { fromLang: PIVOT_LANGUAGE, toLang: "es" },
+  { fromLang: "es", toLang: PIVOT_LANGUAGE },
+  { fromLang: PIVOT_LANGUAGE, toLang: "fr" },
+  { fromLang: "fr", toLang: PIVOT_LANGUAGE },
+  { fromLang: PIVOT_LANGUAGE, toLang: "pl" },
+  { fromLang: "pl", toLang: PIVOT_LANGUAGE },
+];
+
+async function runLangTagsTest(
+  {
+    systemLocales,
+    appLocales,
+    webLanguages,
+    page,
+    languagePairs = LANGUAGE_PAIRS,
+  },
+  langTags
+) {
+  const cleanupLocales = await mockLocales({
+    systemLocales,
+    appLocales,
+    webLanguages,
+  });
+
+  const { cleanup: cleanupTestPage } = await loadTestPage({
+    page,
+    languagePairs,
+  });
+  const actor = getTranslationsParent();
+
+  await TestUtils.waitForCondition(
+    async () => (await actor.getLangTagsForTranslation())?.docLangTag,
+    "Waiting for a document language tag to be found."
+  );
+
+  Assert.deepEqual(await actor.getLangTagsForTranslation(), langTags);
+
+  await cleanupLocales();
+  await cleanupTestPage();
+}
+
+add_task(async function test_lang_tags_direct_translations() {
+  info(
+    "Test the detected languages for translations when a translation pair is available"
+  );
+  await runLangTagsTest(
+    {
+      systemLocales: ["en"],
+      appLocales: ["en"],
+      webLanguages: ["en"],
+      page: TRANSLATIONS_TESTER_ES,
+    },
+    {
+      docLangTag: "es",
+      userLangTag: "en",
+      isDocLangTagSupported: true,
+    }
+  );
+});
+
+add_task(async function test_lang_tags_with_pivots() {
+  info("Test the detected languages for translations when a pivot is needed.");
+  await runLangTagsTest(
+    {
+      systemLocales: ["fr"],
+      appLocales: ["fr", "en"],
+      webLanguages: ["fr", "en"],
+      page: TRANSLATIONS_TESTER_ES,
+    },
+    {
+      docLangTag: "es",
+      userLangTag: "fr",
+      isDocLangTagSupported: true,
+    }
+  );
+});
+
+add_task(async function test_lang_tags_with_pivots_second_preferred() {
+  info(
+    "Test using a pivot language when the first preferred lang tag doesn't match"
+  );
+  await runLangTagsTest(
+    {
+      systemLocales: ["it"],
+      appLocales: ["it", "en"],
+      webLanguages: ["it", "en"],
+      page: TRANSLATIONS_TESTER_ES,
+    },
+    {
+      docLangTag: "es",
+      userLangTag: "en",
+      isDocLangTagSupported: true,
+    }
+  );
+});
+
+add_task(async function test_lang_tags_with_non_supported_doc_language() {
+  info("Test using a pivot language when the doc language isn't supported");
+  await runLangTagsTest(
+    {
+      systemLocales: ["fr"],
+      appLocales: ["fr", "en"],
+      webLanguages: ["fr", "en"],
+      page: TRANSLATIONS_TESTER_ES,
+      languagePairs: [
+        { fromLang: PIVOT_LANGUAGE, toLang: "fr" },
+        { fromLang: "fr", toLang: PIVOT_LANGUAGE },
+        // No Spanish support.
+      ],
+    },
+    {
+      docLangTag: "es",
+      userLangTag: "fr",
+      isDocLangTagSupported: false,
+    }
+  );
+});

toolkit/components/translations/tests/browser/shared-head.js

@@ -275,6 +275,15 @@ async function reorderingTranslator(message) {
   return [translatedDoc.body.innerHTML];
 }
 
+/**
+ * @returns {import("../../actors/TranslationsParent.sys.mjs").TranslationsParent}
+ */
+function getTranslationsParent() {
+  return gBrowser.selectedBrowser.browsingContext.currentWindowGlobal.getActor(
+    "Translations"
+  );
+}
+
 /**
  * This is for tests that don't need a browser page to run.
  */
@@ -306,14 +315,8 @@ async function setupActorTest({
     true // waitForLoad
   );
 
-  /** @type {import("../../actors/TranslationsParent.sys.mjs").TranslationsParent} */
-  const actor =
-    gBrowser.selectedBrowser.browsingContext.currentWindowGlobal.getActor(
-      "Translations"
-    );
-
   return {
-    actor,
+    actor: getTranslationsParent(),
     remoteClients,
     cleanup() {
       BrowserTestUtils.removeTab(tab);