[Investigate] Environment File/Variable Support

[ncalteen]

The workflow commands documentation refers to a number of environment variables that point to files in the GitHub Actions runtime environment. Namely the following:

Variable	Description	Equivalent @actions/core Function
GITHUB_PATH	Add values to the job's PATH	addPath()
GITHUB_ENV	Export environment variables	exportVariable()
GITHUB_STATE	Save state information	saveState()
GITHUB_STEP_SUMMARY	Edit the step summary	summary()
GITHUB_OUTPUT	Set output values	setOutput()

There are also environment variables that map to various @actions/core functions:

Variable	Description	Equivalent @actions/core Function
INPUT_{NAME}	Get an input value	getInput()
STATE_{NAME}	Get a state value	getState()
RUNNER_DEBUG	Check if in debug mode	isDebug()

It would be helpful to investigate if there's a way to map access to these environment variables to the corresponding functionality.

[ncalteen]

Digging into the @actions/core code, these are mainly used via the issueCommand and issueFileCommand functions (here). Adding this functionality would mainly be beneficial in cases where developers are mixing their use of @actions/core and direct access to the environment variables themselves.

E.g. Suppose I save a state value by writing to GITHUB_STATE directly via fs.appendFileSync. After that, I try to read the value using getState(). Currently, this won't work, since @github/local-action doesn't read or touch these files. All such calls instead update information stored in the CoreMeta/EnvMeta objects.

I suppose it could be implemented so that both were supported. Perhaps a file watcher to track when the environment file is written to directly, and keeping the CoreMeta object in sync.

fs.watch(process.env.GITHUB_ENV, (eventType, filename) => {
  if (eventType === 'change') {
    // Read the updated file
    // Sync EnvMeta.env
  }
});

If there are folks who would find this useful, please feel free to add a reaction/comment/etc!