Implement custom element construction and some 'define' checks

third_party/WebKit/Source/bindings/core/v8/custom/V8HTMLElementCustom.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "bindings/core/v8/V8HTMLElement.h"
+
+#include "bindings/core/v8/DOMWrapperWorld.h"
+#include "bindings/core/v8/ExceptionState.h"
+#include "bindings/core/v8/V8Binding.h"
+#include "bindings/core/v8/V8ThrowException.h"
+#include "core/dom/Document.h"
+#include "core/dom/custom/CustomElementDefinition.h"
+#include "core/dom/custom/CustomElementsRegistry.h"
+#include "core/frame/LocalDOMWindow.h"
+#include "platform/RuntimeEnabledFeatures.h"
+
+namespace blink {
+
+void V8HTMLElement::constructorCustom(
+    const v8::FunctionCallbackInfo<v8::Value>& info)
+{
+    DCHECK(info.IsConstructCall());
+    v8::Isolate* isolate = info.GetIsolate();
+
+    if (!RuntimeEnabledFeatures::customElementsV1Enabled()
+        || !DOMWrapperWorld::current(isolate).isMainWorld()) {
+        V8ThrowException::throwIllegalConstructorTypeError(isolate);
+        return;
+    }
+
+    Document* document = toDocument(currentExecutionContext(isolate));
+    v8::Local<v8::Context> context = isolate->GetCurrentContext();
+    CustomElementDefinition* def =
+        document->domWindow()->customElements()->definitionForConstructor(
+            context,
+            info.NewTarget());
+    if (!def) {
+        V8ThrowException::throwIllegalConstructorTypeError(isolate);
+        return;
+    }
+
+    // TODO(dominicc): Implement cases where the definition's
+    // construction stack is not empty when parser-creation is
+    // implemented.
+    ExceptionState exceptionState(
+        ExceptionState::ConstructionContext,
+        "HTMLElement",
+        info.Holder(),
+        isolate);
+    Element* element = document->createElement(
+        def->localName(),
+        AtomicString(),
+        exceptionState);
+    if (exceptionState.throwIfNeeded())
+        return;
+    v8::Local<v8::Object> wrapper = element->wrap(isolate, info.Holder());

[Yuki, 2016/05/11 01:59:02]

Please prefer using toV8() rather than wrap() method.
It's not well-documented, but toV8() is designed to be responsible for the
conversion from C++ DOM object to the corresponding V8 wrapper.  wrap() method
is designed to be used in toV8().

+    info.GetReturnValue().Set(wrapper);

[haraken, 2016/05/10 09:04:22]

Can we use v8SetReturnValue(info, wrapper)?

I'm a bit concerned that this constructorCustom is very hand-written. I hope
you'd copy & paste the generated code and modify only the part you really need
to edit. That way we can minimize a risk of causing bugs due to hand-written
bindings.

[yosin_UTC9, 2016/05/10 13:10:59]

I think we don't need to set return value for constructor since constructor
doesn't return value.
Note: my v8 host works fine w/o setting return value.

[dominicc (has gone to gerrit), 2016/05/11 02:31:49]

Hmm, I actually did start with the HTMLElement constructor, and borrowed the
document lookup from Image (these should be consistent!)

I made some changes to use more ScriptState, PTAL.

[dominicc (has gone to gerrit), 2016/05/11 02:31:49]

We do in this case because we are returning a different value to 'this'.

[yosin_UTC9, 2016/05/11 03:49:55]

AFIK, return value of constructor isn't used. I tried to return |undefined|
value, e.g. info.GetReturnValue().SetUndefined().
It still works.

+    if (wrapper.IsEmpty())
+        return;
+
+    v8::Maybe<bool> couldSetPrototype =
+        wrapper->SetPrototype(context, def->prototype(isolate));

[yosin_UTC9, 2016/05/10 13:10:59]

Can we use new.target.constructor.prototype? If so we can extend class implement
custom-element.

class X extends HTMLElement { ... } // from comment#1
class Y extends Y { .... } // extends X

Setting prototype from |def| makes (new Y()).__proto__ == X.__proto__


const auto& prototype = info.NewTarget().As<v8::Function>()->Get("prototype");
wrapper->SetPrototype(context, prototype);

It works fine for my v8 host. ;-)

BTW, I'm asking V8 does above:
https://bugs.chromium.org/p/v8/issues/detail?id=5001

[dominicc (has gone to gerrit), 2016/05/11 02:31:49]

I was wondering about this too; I filed
https://github.com/whatwg/html/issues/1229
Looks like verwaest got back to you on the bug. I was surprised it didn't. We
have to set the prototype explicitly here per the spec so we don't really
benefit from this.

[yosin_UTC9, 2016/05/11 03:49:55]

Can we change spec to pass tagName to super? If so, we don't need to have
customer constructor at all.

class X extends HTMLElement { constructor() { super('some-thing'); } }

+    if (couldSetPrototype.IsNothing())
+        return;
+    if (!couldSetPrototype.FromJust()) {

[haraken, 2016/05/10 09:04:22]

V8BindingMacros.h provides macros to avoid developers from using IsNothing,
FromJust etc. Can we replace these with the macro?

+        // TODO(dominicc): Find out when SetPrototype can fail and write a
+        // test for this.

[haraken, 2016/05/10 09:04:22]

You can use v8CallOrCrash. (In practice, it will never crash except OOM.)

+        return;
+    }
+}
+
+} // namespace blink