Bug 174006 – Web Inspector: Add Runtime.await to run an await expression (like Runtime.evaluate)

• Component: Web Inspector
• Status: NEW

[Joseph Pecoraro]

We have an `await` convenience in the console that will allow you to await an asynchronous result.

Currently it works like:

    > await fetch("data.json")
    < undefined
    [Info] Response {type: "basic", url: "data.json", redirected: false, status: 200, ok: true, …}

It would be nicer to:

  - Not output the `undefined`, instead include a "Awaiting..." message
  - Replace the message with the result
  - Save results with a $n value as expected

So you would get:

    > await fetch("data.json")
    [Icon] Running...

And later:

    > await fetch("data.json")
    < Response {type: "basic", url: "data.json", redirected: false, status: 200, ok: true, …} = $1

I propose we have a `Runtime.await` which is just an async version of `Runtime.evaluate`.

[Joseph Pecoraro]

Created attachment 314210 [details]
[PATCH] Work in Progress (Needs Test and Async UI tweaks)

This is the idea I have. It works in practice. I have to move onto other things at the moment though.

This would need tests and the UI tweaks during an async evaluation.

I did implement an awaitOnCallFrame but currently when paused we don't seem to run the promise microtasks. So effectively you don't get the result until you resume / continue. So I left that out of this given the pre-existing issues.

[Joseph Pecoraro]

Comment on attachment 314210 [details]
[PATCH] Work in Progress (Needs Test and Async UI tweaks)

View in context: https://bugs.webkit.org/attachment.cgi?id=314210&action=review

> Source/JavaScriptCore/inspector/JSInjectedScriptCallback.h:41
> +class JSInjectedScriptCallback : public JSC::InternalFunction {
> +public:
> +    typedef InternalFunction Base;
> +
> +    static JSInjectedScriptCallback* create(JSC::VM&, JSC::JSGlobalObject*, WTF::Function<void(JSC::ExecState*)>&&);

@Saam / Mark: Is this a bad idea? I'm basically making a Function that wraps a lambda. So we can:

    auto callback = JSInjectedScriptCallback(vm, globalObject, [](ExecState *exec) {
        JSValue a = exec->argument(0);
        JSValue b = exec->argument(1);
        JSValue c = exec->argument(2);
        ...
    });

We pass this off to Inspector JavaScript so that when it invokes `callback(a, b, c)` the lambda can deal with it.

With this approach we need to be worried about object lifetimes (if `this` is used by the lamba) but maybe there is an easier way to do the same thing as this?

[Radar WebKit Bug Importer]

<rdar://problem/33122054>