Bug 1415761 - Catch the exception and rethrow it after invoking custom elements reactions;

The spec was unclear on how CEReactions interact with thrown exceptions; see https://github.com/whatwg/html/issues/3217. The spec is now being clarified in https://github.com/whatwg/html/pull/3235.

Tag UXP Issue #1344

dom/base/CustomElementRegistry.h

@@ -472,15 +472,24 @@ public:
 
 class MOZ_RAII AutoCEReaction final {
   public:
-    explicit AutoCEReaction(CustomElementReactionsStack* aReactionsStack)
+    // JSContext is allowed to be a nullptr if we are guaranteeing that we're
-      : mReactionsStack(aReactionsStack) {
+    // not doing something that might throw but not finish reporting a JS
+    // exception during the lifetime of the AutoCEReaction.
+    AutoCEReaction(CustomElementReactionsStack* aReactionsStack, JSContext* aCx)
+      : mReactionsStack(aReactionsStack)
+      , mCx(aCx) {
       mReactionsStack->CreateAndPushElementQueue();
     }
     ~AutoCEReaction() {
+      Maybe<JS::AutoSaveExceptionState> ases;
+      if (mCx) {
+        ases.emplace(mCx);
+      }
       mReactionsStack->PopAndInvokeElementQueue();
     }
   private:
     RefPtr<CustomElementReactionsStack> mReactionsStack;
+    JSContext* mCx;
 };
 
 } // namespace dom

dom/base/nsDocument.cpp

@@ -5809,7 +5809,8 @@ nsDocument::RegisterElement(JSContext* aCx, const nsAString& aType,
     return;
   }
 
-  AutoCEReaction ceReaction(this->GetDocGroup()->CustomElementReactionsStack());
+  AutoCEReaction ceReaction(this->GetDocGroup()->CustomElementReactionsStack(),
+                            aCx);
   // Unconditionally convert TYPE to lowercase.
   nsAutoString lcType;
   nsContentUtils::ASCIIToLower(aType, lcType);

dom/bindings/Codegen.py

@@ -7679,7 +7679,7 @@ class CGPerSignatureCall(CGThing):
                 CustomElementReactionsStack* reactionsStack = GetCustomElementReactionsStack(${obj});
                 Maybe<AutoCEReaction> ceReaction;
                 if (reactionsStack) {
-                  ceReaction.emplace(reactionsStack);
+                    ceReaction.emplace(reactionsStack, cx);
                 }
                 """, obj=objectName)))
 

js/xpconnect/tests/mochitest/test_bug1094930.html

@@ -16,14 +16,14 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1094930
 <script type="application/javascript">
   SimpleTest.waitForExplicitFinish();
   var proto = { 
-    createdCallback: function() {
+    connectedCallback: function() {
-      ok(true, "createdCallback was called");
+      ok(true, "connectedCallback was called");
       SimpleTest.finish()
     }
   };
 
   var f = document.registerElement.call(frames[0].document, "x-foo", { prototype: proto });
-  var inst = new f();
+  frames[0].document.firstChild.appendChild(new f());
 </script>
 </body>
 </html>

parser/html/nsHtml5TreeOperation.cpp

@@ -450,7 +450,8 @@ nsHtml5TreeOperation::CreateHTMLElement(
       nsAutoMicroTask mt;
     }
     dom::AutoCEReaction
-      autoCEReaction(document->GetDocGroup()->CustomElementReactionsStack());
+      autoCEReaction(document->GetDocGroup()->CustomElementReactionsStack(),
+                     nullptr);
 
     nsCOMPtr<dom::Element> newElement;
     NS_NewHTMLElement(getter_AddRefs(newElement), nodeInfo.forget(),

testing/web-platform/tests/custom-elements/reactions/with-exceptions.html

@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Custom Elements: CEReactions interaction with exceptions</title>
+<link rel="author" title="Domenic Denicola" href="mailto:d@domenic.me">
+<meta name="help" content="https://html.spec.whatwg.org/multipage/#cereactions">
+<meta name="help" content="https://github.com/whatwg/html/pull/3235">
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../resources/custom-elements-helpers.js"></script>
+
+<div id="log"></div>
+
+<script>
+"use strict";
+// Basically from https://github.com/whatwg/html/issues/3217#issuecomment-343633273
+test_with_window((contentWindow, contentDocument) => {
+  let reactionRan = false;
+  contentWindow.customElements.define("custom-element", class extends contentWindow.HTMLElement {
+    disconnectedCallback() {
+      reactionRan = true;
+    }
+  });
+  const text = contentDocument.createTextNode("");
+  contentDocument.documentElement.appendChild(text);
+  const element = contentDocument.createElement("custom-element");
+  contentDocument.documentElement.appendChild(element);
+  assert_throws("HierarchyRequestError", () => text.before("", contentDocument.documentElement));
+  assert_true(reactionRan);
+}, "Reaction must run even after the exception is thrown");
+</script>