Issue 1489 - Support preconfigured defaults

lib/prefs.js

 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 let {addonRoot, addonName} = require("info");
 let branchName = "extensions." + addonName + ".";
 let branch = Services.prefs.getBranch(branchName);
 let ignorePrefChanges = false;
 
 function init()
 {
   // Load default preferences and set up properties for them
   let defaultBranch = Services.prefs.getDefaultBranch(branchName);
   let scope =
   {
     pref: function(pref, value)
     {
       if (pref.substr(0, branchName.length) != branchName)
       {
         Cu.reportError(new Error("Ignoring default preference " + pref + ", wrong branch."));
         return;
       }
       pref = pref.substr(branchName.length);
 
       let [getter, setter] = typeMap[typeof value];
-      setter(defaultBranch, pref, value);
+      if (!hasPreconfiguredDefault(branch, pref))
+        setter(defaultBranch, pref, value);
+
       defineProperty(pref, false, getter, setter);
     }
   };
   Services.scriptloader.loadSubScript(addonRoot + "defaults/prefs.js", scope);
 
   // Add preference change observer
   try
   {
     branch.QueryInterface(Ci.nsIPrefBranch2).addObserver("", Prefs, true);
     onShutdown.add(function() branch.removeObserver("", Prefs));
   }
   catch (e)
   {
     Cu.reportError(e);
   }
 }
 
 /**
+ * Checks whether the supplied pref has a preconfigured default value.
+ */
+function hasPreconfiguredDefault(branch, pref)
+{
+  try
+  {
+    let defaults = getJSONPref(branch, "preconfigured_defaults");
+    return defaults.indexOf(pref) != -1;
+  }
+  catch (e)
+  {
+    return false;
+  }
+}
+
+/**
  * Sets up getter/setter on Prefs object for preference.
  */
 function defineProperty(/**String*/ name, defaultValue, /**Function*/ readFunc, /**Function*/ writeFunc)
 {
   let value = defaultValue;
   Prefs["_update_" + name] = function()
   {
     try
     {
       value = readFunc(branch, name);
@@ skipping 123 matching lines @@
 {
   let str = Cc["@mozilla.org/supports-string;1"].createInstance(Ci.nsISupportsString);
   str.data = newValue;
   branch.setComplexValue(pref, Ci.nsISupportsString, str);
 }
 
 function getJSONPref(branch, pref) JSON.parse(getCharPref(branch, pref))
 function setJSONPref(branch, pref, newValue) setCharPref(branch, pref, JSON.stringify(newValue))
 
 init();