yarn berry: Monitoring stdout output inside a wrapScriptExecution hook.

[mm-zacharydavison]

We have some tooling that monitors script output in order to collect some analytics.

In npm based environments, we used to do this by shimming the script shell using the script-shell parameter of .npmrc, but this has been removed in yarn berry.

It seems like wrapScriptExecution could fulfill the same purpose, but the part that we can't quite figure out is how we can hook into the stdout of the subprocess thats spawned to run the script.

Just waiting for the script to return isn't an option, because we do this for indeterminate scripts (e.g. like running a local node.js webserver).

I noticed that the output of the script is actually written to a logFile here, which we could use to monitor output, except it's difficult to get a handle on the filename at runtime, since it's a temporary file.

I notice that wrapScriptExecution hooks do get stdout and stderr streams passed to them in extra, but these are Writable streams, and the stdout output isn't piped through to them.

How can we do this using wrapScriptExecution?