FR: Ability for process_wrapper to write exit code to a file instead of forwarding it

[blorente]

Problem

Currently, the process_wrapper forwards the exit code of a given child process. As a result, if the child process fails, so will the process_wrapper, and the action running it.

This makes it impossible to do things like post-processing linter outputs.

Specifically, I want to call rust_clippy_action from my own rules (rules_lint). I want to do some post-processing to clippy's output in a further action down the line (e.g. to generate reports in a different format). Clippy may generate both warnings and errors, and return with a non-zero code if there is at least one error.

Imagine my code has one warning and one error. I have two options:

• Let the entire build fail because there was one error, or
• Demote all errors to warnings so that clippy succeeds, which loses me information about which problems were actually errors.

Proposal

I'd like to add two arguments to process_wrapper:

• --forward-exit-code (boolean): If set, the process_wrapper will exit with the same exit code as the subprocess if it had no internal errors.
• --exit-code-file (String): If set, the exit code of the child process will be written to this file. Unset by default.

This allows callers a lot more control over how they want to treat errors, and should be an invisible change for existing users.

However, it touches a fundamental API ( the process_wrapper), so I thought better to ask first: Would this be an acceptable change?