node: need a way to spawn process.execPath with no deno specific flags

Describe the bug Many Node.js tests spawn the node executable in a child process. This is separate from child_process.fork(). As an example, see this test. The problem in that test is that in Deno’s compat mode, the spawnSync() call needs to be updated to pass in necessary Deno CLI flags (-A, --unstable, etc.).

For users, this is a problem because they can’t run existing Node code as is. For us, it’s also a problem because by modifying the Node tests, we lose the ability to automatically upgrade them to newer versions of Node.

A few ideas on how to approach this:

• In the compat code, detect when we are spawning the current executable and set an environment variable that allows Deno to start up properly with no CLI flags. This would require changes in core.
• In the compat code, detect when we are spawning the current executable and add the CLI flags. This could be done in std alone, but might have some edge cases.

Steps to Reproduce

Spawn process.execPath in Node compat mode without changing any of the CLI flags.

Expected behavior

Node compat code runs without modifications.

Environment

• OS: all
• deno version: 1.25.3
• std version: 0.156.0

[cjihrig]

Discussed this internally today. The plan is to land https://github.com/denoland/deno_std/pull/2688 and begin working on a Node argument parser in Deno. Once that is ready, the mapping logic in #2688 can be ripped back out.

[lino-levan]

Compat mode no longer exists, is this still relevant? #2688 landed a while ago and I haven’t seen a lot of movement on this issue. If there is something to be done, I’d love to pick it up.