Bug 1254978 - Set blank if the current font is not installed and the font backend does not support language-specific enumeration. r=Gijs

browser/components/preferences/in-content/tests/browser_basic_rebuild_fonts_test.js

@@ -20,5 +20,57 @@ add_task(function() {
   let fontSizeField = doc.getElementById("defaultFontSize");
   is(fontSizeField.value, defaultFontSize, "Font size should be set correctly.");
 
+  doc.getElementById("advancedFonts").click();
+  let win = yield promiseLoadSubDialog("chrome://browser/content/preferences/fonts.xul");
+  doc = win.document;
+
+  // Simulate a dumb font backend.
+  win.FontBuilder._enumerator = {
+    _list: ["MockedFont1", "MockedFont2", "MockedFont3"],
+    EnumerateFonts: function(lang, type, list) {
+      return this._list;
+    },
+    EnumerateAllFonts: function() {
+      return this._list;
+    },
+    getDefaultFont: function() { return null; },
+    getStandardFamilyName: function(name) { return name; },
+  };
+  win.FontBuilder._allFonts = null;
+  win.FontBuilder._langGroupSupported = false;
+
+  let langGroupElement = doc.getElementById("font.language.group");
+  let selectLangsField = doc.getElementById("selectLangs");
+  let serifField = doc.getElementById("serif");
+  let armenian = "x-armn";
+  let western = "x-western";
+
+  langGroupElement.value = armenian;
+  selectLangsField.value = armenian;
+  is(serifField.value, "", "Font family should not be set.");
+
+  langGroupElement.value = western;
+  selectLangsField.value = western;
+
+  // Simulate a font backend supporting language-specific enumeration.
+  // NB: FontBuilder has cached the return value from EnumerateAllFonts(),
+  // so _allFonts will always have 3 elements regardless of subsequent
+  // _list changes.
+  win.FontBuilder._enumerator._list = ["MockedFont2"];
+
+  langGroupElement.value = armenian;
+  selectLangsField.value = armenian;
+  is(serifField.value, "MockedFont2", "Font family should be set.");
+
+  langGroupElement.value = western;
+  selectLangsField.value = western;
+
+  // Simulate a system that has no fonts for the specified language.
+  win.FontBuilder._enumerator._list = [];
+
+  langGroupElement.value = armenian;
+  selectLangsField.value = armenian;
+  is(serifField.value, "", "Font family should not be set.");
+
   gBrowser.removeCurrentTab();
 });

toolkit/mozapps/preferences/fontbuilder.js

@@ -16,6 +16,7 @@ var FontBuilder = {
   },
 
   _allFonts: null,
+  _langGroupSupported: false,
   buildFontList: function (aLanguage, aFontType, aMenuList)
   {
     // Reset the list
@@ -62,6 +63,7 @@ var FontBuilder = {
 
     // Build the UI for the remaining fonts.
     if (this._allFonts.length > fonts.length) {
+      this._langGroupSupported = true;
       // Both lists are sorted, and the Fonts-By-Type list is a subset of the
       // All-Fonts list, so walk both lists side-by-side, skipping values we've
       // already created menu items for.
@@ -102,7 +104,10 @@ var FontBuilder = {
         return undefined;
     }
 
-    let defaultValue = aElement.firstChild.firstChild.getAttribute("value");
+    // The first item will be a reasonable choice only if the font backend
+    // supports language-specific enumaration.
+    let defaultValue = this._langGroupSupported ?
+                       aElement.firstChild.firstChild.getAttribute("value") : "";
     let fontNameList = preference.name.replace(".name.", ".name-list.");
     let prefFontNameList = document.getElementById(fontNameList);
     if (!prefFontNameList || !prefFontNameList.value)