Bug 438599 - the currentEngine attribute of nsIBrowserSearchService should never be null, r=Mossop.

toolkit/components/search/nsSearchService.js

@@ -4916,6 +4916,14 @@ SearchService.prototype = {
       this._currentEngine = this._originalDefaultEngine;
     if (!this._currentEngine || this._currentEngine.hidden)
       this._currentEngine = this._getSortedEngines(false)[0];
+
+    if (!this._currentEngine) {
+      // Last resort fallback: unhide the original default engine.
+      this._currentEngine = this._originalDefaultEngine;
+      if (this._currentEngine)
+        this._currentEngine.hidden = false;
+    }
+
     return this._currentEngine;
   },
 

toolkit/components/search/tests/xpcshell/test_currentEngine_fallback.js

@@ -0,0 +1,25 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function run_test() {
+  do_check_true(Services.search.getVisibleEngines().length > 1);
+  do_check_true(Services.search.isInitialized);
+
+  // Remove the current engine...
+  let currentEngine = Services.search.currentEngine;
+  Services.search.removeEngine(currentEngine);
+
+  // ... and verify a new current engine has been set.
+  do_check_neq(Services.search.currentEngine.name, currentEngine.name);
+  do_check_true(currentEngine.hidden);
+
+  // Remove all the other engines.
+  Services.search.getVisibleEngines().forEach(Services.search.removeEngine);
+  do_check_eq(Services.search.getVisibleEngines().length, 0);
+
+  // Verify the original default engine is used as a fallback and no
+  // longer hidden.
+  do_check_eq(Services.search.currentEngine.name, currentEngine.name);
+  do_check_false(currentEngine.hidden);
+  do_check_eq(Services.search.getVisibleEngines().length, 1);
+}

toolkit/components/search/tests/xpcshell/xpcshell.ini

@@ -82,3 +82,4 @@ tags = addons
 [test_selectedEngine.js]
 [test_geodefaults.js]
 [test_hidden.js]
+[test_currentEngine_fallback.js]