Walkthrough

The changes enable preexec_fn support in subprocess execution by removing a not-implemented guard, threading the VM reference through function signatures from fork_exec to exec_inner, adding a new PreExec variant to ExecErrorContext for error distinction, and implementing preexec_fn invocation in the child process after setup but before file descriptor closing.

Changes

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 A preexec hop through code we go,
With VMs passed where children flow,
Callbacks bloom before execve's call,
Error messages catch one and all—
Subprocess magic, clean and bright!

• 📝 Generate docstrings

• Create PR with unit tests
• Post copyable unit tests in a comment

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Reviewing files that changed from the base of the PR and between 309b2ad and c7fcd56.

• Lib/test/test_subprocess.py is excluded by !Lib/**

• crates/stdlib/src/posixsubprocess.rs

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