Bug 1173385 - Calling $$("") should throw an exception. r=fitzgen

toolkit/devtools/server/actors/webconsole.js

@@ -811,18 +811,14 @@ WebConsoleActor.prototype =
     if (evalResult) {
       if ("return" in evalResult) {
         result = evalResult.return;
-      }
-      else if ("yield" in evalResult) {
+      } else if ("yield" in evalResult) {
         result = evalResult.yield;
-      }
-      else if ("throw" in evalResult) {
+      } else if ("throw" in evalResult) {
         let error = evalResult.throw;
         errorGrip = this.createValueGrip(error);
-        let errorToString = evalInfo.window
-                            .evalInGlobalWithBindings("ex + ''", {ex: error});
-        if (errorToString && typeof errorToString.return == "string") {
-          errorMessage = errorToString.return;
-        }
+        errorMessage = error && (typeof error === "object")
+          ? error.unsafeDereference().toString()
+          : "" + error;
       }
     }
 

toolkit/devtools/webconsole/test/test_jsterm_queryselector.html

@@ -23,7 +23,11 @@ function startTest() {
   removeEventListener("load", startTest);
   attachConsole([], state => {
     gState = state;
-    let tests = [checkQuerySelectorAll, checkQuerySelectorAllNotExist];
+    let tests = [
+      checkQuerySelectorAll,
+      checkQuerySelectorAllNotExist,
+      checkQuerySelectorAllException
+    ];
     runTests(tests, testEnd);
   }, true);
 }
@@ -54,6 +58,23 @@ let checkQuerySelectorAllNotExist = Task.async(function*() {
   nextTest();
 });
 
+let checkQuerySelectorAllException = Task.async(function*() {
+  info ("$$ returns an exception if an invalid selector was provided");
+  let response = yield evaluateJS("$$(':foo')");
+  checkObject(response, {
+    input: "$$(':foo')",
+    exceptionMessage: "SyntaxError: An invalid or illegal string was specified",
+    exception: {
+      preview: {
+        kind: "DOMException",
+        name: "SyntaxError",
+        message: "An invalid or illegal string was specified"
+      }
+    }
+  });
+  nextTest();
+});
+
 function basicResultCheck(response, input, output) {
   checkObject(response, {
     from: gState.actor,