andreubotella / deno_test262 Goto Github PK

$262 is a host-defined object that must exist as a property of the global object in test262 tests, and which allows it to test a number of things in the TC39 specification that can't be merely triggered from JS alone:

• $262.createRealm(). Not currently implementable because Deno doesn't support realms.
• $262.detachArrayBuffer(). #28
• $262.evalScript(). #22
• $262.gc()
• $262.global
• $262.IsHTMLDDA. Not implementable because Deno doesn't support the DOM or document.all.
• $262.agent.start(). #30
• $262.agent.broadcast(). #55
• $262.agent.getReport()
• $262.agent.sleep()
• $262.agent.monotonicNow()

Test262's $262.agent APIs deal with running code in a different agent, in order to test SharedArrayBuffer, Atomics and similar APIs. In Deno the only way to have multiple agents is with workers.

The $262.agent.start() function must start an agent and block until the script passed as the first parameter is running in the agent. The only way to block until the worker is running is by sending a SharedArrayBuffer with worker.postMessage() and using Atomics.wait() to block on it – with the worker only running the code in the message event listener, after unblocking and notifying the main thread.

Since the global object inside agents created with $262.agent.start() must also be modified before the code can run (see #31), it would seem like the best solution for both things is to have an agent-setup.js file that serves as the workers' main module, and which sets up the global object and listens for the message event. The code to run in the agent is then passed as part of the first message, along with the SharedArrayBuffer.

The built-ins/Object/defineProperties/15.2.3.7-2-18.js test fails with:

Test262Error {
  message: 'Expected TypeError, got ReferenceError: Access to "location", run again with --location <href>.'
}

This is because the test runs Object.defineProperties(obj, this), where this is the global object, and Object.defineProperties() gets all of the second argument's properties, including globalThis.location, which throws when getting if the --location argument isn't passed.

This can't be worked around by deleting globalThis.location in the test runner because globalThis.location is non-configurable (due to the LegacyUnforgeable WebIDL attribute). The only way to work around this seems to be to set the --location flag to a dummy URL, like http://example.com

Transferring ArrayBuffer objects was enabled in denoland/deno#11840, and it will land on Deno 1.14. This will allow detaching ArrayBuffers, which will let us implement this host-defined function required by test262.

Here's an example of detaching an ArrayBuffer in the current Deno canary:

> let buffer = new ArrayBuffer(1024);
undefined
> structuredClone(undefined, {transfer: [buffer]})
undefined
> new Uint8Array(buffer)
Uncaught TypeError: Cannot perform Construct on a detached ArrayBuffer
    at new Uint8Array (<anonymous>)
    at <anonymous>:2:1

And the corresponding agent function $262.agent.receiveBroadcast().

Inside an agent created with $262.agent.start(), there is a $262.agent object, but its properties are different functions from those in the main agent's $262.agent:

• $262.agent.receiveBroadcast(). Counterpart to the main agent's $262.agent.broadcast(). #55
• $262.agent.report(). Counterpart to the main agent's $262.agent.getReport().
• $262.agent.sleep(). Same as the main agent's $262.agent.sleep().
• $262.agent.leaving()
• $262.agent.monotonicNow(). Same as the main agent's $262.agent.monotonicNow().