v8: introduce v8.emitCodeGenFromStringEvent()

[vdeturckheim]

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

As of today, it is not possible to intercept calls made to eval as the method can't really be monkeypatched without breaking its behavior.
Thanksfully there is an API in V8 that can be used to place a callback when code is generated from string (eval and new Function(string). This PR introduces a way to listen on theses events from userland.

If the --disallow-code-generation-from-strings flag is used, calling emitCodeGenFromStringEvent will have no effect as calls to eval and new Function will fail anyway.

After calling v8.emitCodeGenFromStringEvent(), each time a call is made to eval or new function, an codeGenerationFromString event will be emitted on process with the code as argument.

cc @fraxken @bmeck @cjihrig @targos :)

[devsnek]

I will need to think about this more but my initial thought here is that this should be scoped to vm contexts.

[addaleax]

Wouldn’t it be easier to do the same thing we do for e.g. the signal events, that is, use process.on('newListener') and process.on('removeListener') to check whether there are any listeners for this event, and if so, enable the feature?

[vdeturckheim]

@devsnek that's a very fair point. I considered it too. AFAIK, vm is used to instanciate modules and enabling this could lead to potential perf issues on this path if the listeners are slow. Also, such behavior can be added to vm through monkeypatching so I don't have a real need for this there.
I settled with handling only the capabilities of the V8 API there but it might not be the more logical path.

@addaleax I explored a bit in this direction. The issue I met was that the flow of disabling it is pretty sensitive:
The state of --disallow-code-generation-from-strings should be respected so we might need ot add some kind of state somewhere to check if the value of IsCodeGenerationFromStringsAllowed() is set at process level or not.

Given that this is a bit niche, I went with this simpler API. But what you suggest is a good UX IMO so I'm open to move toward that (I will maybe need a hand to decide where to put this state I'm mentionning).

[devsnek]

I'm really just not sure that this should exist at the scope of the main node context. Probably at worst it can leak implementation details between libraries.

[vdeturckheim]

@devsnek do you think there could be another way to audit calls made to eval at runtime? This is actually the end goal of this PR for me.

[devsnek]

@vdeturckheim a native addon perhaps?

[vdeturckheim]

@devsnek IMO it can be useful to many to have such in core - the user experience of native addons can be pretty complicated in some cases. Also,this makes a feature of V8 available in userland more than creating a new feature.

[vdeturckheim]

@addaleax I think I have a solution actually. I will update soon with something that follows your suggestion 😄

[vdeturckheim]

closing as it is a double of #35157