Support IPC in bun package.json script runner

[yus-ham]

What is the problem this feature would solve?

package.json

{ "scripts": { "mycoolscript":"bun ./child.js"}}

./child.js

process.send('hello')

parent.js

Bun.spawn(['bun', 'mycoolscript'], {
  ipc(message) {
    console.info(message) // hello
  }
})

What is the feature you are proposing to solve the problem?

Make bun script runner as IPC proxy

What alternatives have you considered?

No response

[Jarred-Sumner]

To any contributors who want to do this:

• An environment variable is used to inform the other process about IPC
• In Bun, file descriptors are not inherited when a process spawns (we try to prevent leaking file descriptors as much as possible) which means we mark the IPC file descriptor as "close-on-exec".
• The fix is to make the codepaths which do bun run <package.json script> and bun <package.json script> add the IPC file descriptor as .inherit in the Stdio options if the environment variable exists. Most of this code is in src/cli/run_command.zig

[lpessoa]

Can I have a go at this one? been looking to jump in the zig bandwagon for some time 😄