Bug 1075160 - Support action: reset a pref to the default setting r=gfritzsche, r=bholley

browser/components/selfsupport/SelfSupportService.js

@@ -7,6 +7,7 @@
 const {classes: Cc, interfaces: Ci, utils: Cu} = Components;
 
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+Cu.import("resource://gre/modules/Services.jsm");
 
 const policy = Cc["@mozilla.org/datareporting/service;1"]
                  .getService(Ci.nsISupports)
@@ -63,6 +64,10 @@ MozSelfSupportInterface.prototype = {
       }
     }.bind(this));
   },
+
+  resetPref: function(name) {
+    Services.prefs.clearUserPref(name);
+  },
 }
 
 this.NSGetFactory = XPCOMUtils.generateNSGetFactory([MozSelfSupportInterface]);

browser/components/selfsupport/moz.build

@@ -8,3 +8,7 @@ EXTRA_COMPONENTS += [
     'SelfSupportService.js',
     'SelfSupportService.manifest',
 ]
+
+BROWSER_CHROME_MANIFESTS += [
+    'test/browser.ini',
+]

browser/components/selfsupport/test/browser.ini

@@ -0,0 +1,3 @@
+[DEFAULT]
+
+[browser_selfsupportAPI.js]

browser/components/selfsupport/test/browser_selfsupportAPI.js

@@ -0,0 +1,47 @@
+Cu.import("resource://gre/modules/Preferences.jsm");
+
+function test() {
+  const prefNewName = "browser.newpref.fake";
+  Assert.ok(!Preferences.has(prefNewName), "pref should not exist");
+
+  const prefExistingName = "extensions.hotfix.id";
+  Assert.ok(Preferences.has(prefExistingName), "pref should exist");
+  Assert.ok(!Preferences.isSet(prefExistingName), "pref should not be user-set");
+  let prefExistingOriginalValue = Preferences.get(prefExistingName);
+
+  registerCleanupFunction(function() {
+    Preferences.set(prefExistingName, prefExistingOriginalValue);
+    Services.prefs.deleteBranch(prefNewName);
+  });
+
+  // 1. do nothing on an inexistent pref
+  MozSelfSupport.resetPref(prefNewName);
+  Assert.ok(!Preferences.has(prefNewName), "pref should still not exist");
+
+  // 2. creation of a new pref
+  Preferences.set(prefNewName, 10);
+  Assert.ok(Preferences.has(prefNewName), "pref should exist");
+  Assert.equal(Preferences.get(prefNewName), 10, "pref value should be 10");
+
+  MozSelfSupport.resetPref(prefNewName);
+  Assert.ok(!Preferences.has(prefNewName), "pref should not exist any more");
+
+  // 3. do nothing on an unchanged existing pref
+  MozSelfSupport.resetPref(prefExistingName);
+  Assert.ok(Preferences.has(prefExistingName), "pref should still exist");
+  Assert.equal(Preferences.get(prefExistingName), prefExistingOriginalValue, "pref value should be the same as original");
+
+  // 4. change the value of an existing pref
+  Preferences.set(prefExistingName, "anyone@mozilla.org");
+  Assert.ok(Preferences.has(prefExistingName), "pref should exist");
+  Assert.equal(Preferences.get(prefExistingName), "anyone@mozilla.org", "pref value should have changed");
+
+  MozSelfSupport.resetPref(prefExistingName);
+  Assert.ok(Preferences.has(prefExistingName), "pref should still exist");
+  Assert.equal(Preferences.get(prefExistingName), prefExistingOriginalValue, "pref value should be the same as original");
+
+  // 5. delete an existing pref
+  // deleteBranch is implemented in such a way that
+  // clearUserPref can't undo its action
+  // see discussion in bug 1075160
+}

dom/webidl/MozSelfSupport.webidl

@@ -39,4 +39,15 @@ interface MozSelfSupport
    *         Resolved when the FHR payload data has been collected.
    */
   Promise<object> getHealthReportPayload();
+
+  /**
+   * Resets a named pref:
+   * - if there is a default value, then change the value back to default,
+   * - if there's no default value, then delete the pref,
+   * - no-op otherwise.
+   *
+   * @param DOMString
+   *        The name of the pref to reset.
+   */
+  void resetPref(DOMString name);
 };