src: expose node::MakeContextify to make a node managed vm context

[legendecas]

This allows addons to create a context, with Node.js inspector support.
The created context is identicaly to the one created with vm.createContext
in node:vm. However, node:vm does not allow an addon to unwrap the
v8::Context out of the sandbox object.

The API exposed is intended to be minimum, so that it will not block
the pending vm Modules API.

[nodejs-github-bot]

Review requested:

• @nodejs/gyp

[addaleax]

The created context is identicaly to the one created with vm.createContext
in node:vm. However, node:vm does not allow an addon to unwrap the
v8::Context out of the sandbox object.

The API exposed is intended to be minimum

That kinda sounds like what we primarily need/want is an API to unwrap the v8::Context from a sandbox object – couldn't we do that instead? (It's also not super difficult to do that tbh, you could run vm.runInContext('{}', context) and do obj->GetCreationContext() on the result)

[addaleax]

I'd suggest adding a version field on this struct for easier ABI compatibility if we want to make changes at some point

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.68%. Comparing base (06a8240) to head (c6a39cf).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
src/api/environment.cc	78.57%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #62322   +/-   ##
=======================================
  Coverage   89.68%   89.68%           
=======================================
  Files         676      676           
  Lines      206578   206612   +34     
  Branches    39555    39560    +5     
=======================================
+ Hits       185267   185301   +34     
+ Misses      13446    13445    -1     
- Partials     7865     7866    +1     

Files with missing lines	Coverage Δ
src/node.h	92.98% <100.00%> (+0.67%)	⬆️
src/node_contextify.h	82.35% <ø> (ø)
src/api/environment.cc	79.05% <78.57%> (-0.03%)	⬇️

... and 27 files with indirect coverage changes

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[legendecas]

@addaleax: That kinda sounds like what we primarily need/want is an API to unwrap the v8::Context from a sandbox object – couldn't we do that instead?

Yeah, that's the main purpose. We could expose an API to unwrap the v8::Context out from sandbox object directly. However, I feel like it would be more straitforward to allow addons to create and manage a Node.js managed v8::Context directly, similar to node::NewContext (maybe we should encourage addons to use this new API instead of node::NewContext because it is not configured to support inspector).

[addaleax]

We could expose an API to unwrap the v8::Context out from sandbox object directly.

I still feel like that's both easier and a bit more powerful, but I'll leave it up to you 👍

[legendecas]

I still feel like that's both easier and a bit more powerful

I can add both. A node::MakeContextify could avoid jumping between JS and C++ unnecessarily for creating a context, and as a replacement of node::NewContext. And an unwrap method like you suggested could help dealing with existing vm contexts.