This is awesome @robertbrignull! I am obviously a big fan of this change 😃

Perhaps as a next step we could even compile a single "binary" which all actions could use as their runs.main and control what command to run by means of an input argument. For example:

name: 'CodeQL: Init'
description: 'Setup the CodeQL tracer'
author: 'GitHub'
inputs:
  tools:
    description: URL of CodeQL tools
    required: false
    default: https://github.com/github/codeql-action/releases/download/codeql-bundle-20200601/codeql-bundle.tar.gz
  languages:
    description: The languages to be analysed
    required: false
  token:
    default: ${{ github.token }}
  matrix:
    default: ${{ toJson(matrix) }}
  config-file:
    description: Path of the config file to use
    required: false
+ command:
+   default: "init"
runs:
  using: 'node12'
- main: '../lib/setup-tracer.js'
+ main: '../lib/main.js'

../lib/main.js would then have to multiplex the command input and call the right function from there...

Still setup-tracer.js would remain a special case I suppose.

Thoughts? Btw, I would love to help in any way I can.

Doesn't the fact that all the code gets bundled into a single minified file make conflicts much more likely?

Perhaps as a next step we could even compile a single "binary" which all actions could use as their runs.main and control what command to run by means of an input argument.

@alexkappa, I like the idea of only having one "binary" that we compile. I thought of a different way of then hooking into it by manually writing simple js files like

require('main.js').init()

and

require('main.js').analyze()

I'm not really sure which is best. I find putting the command as an input to the action a little odd as it could produce odd behaviour if a user changed it, and we might be obligated to document what it is. However introducing extra files is also a bit annoying.

Doesn't the fact that all the code gets bundled into a single minified file make conflicts much more likely?

@chrisgavin, yes, you're right it'll increase the chance of conflicts in the minified code. If we bundle all the files but don't minify them that could reduce it. I think we'd still get conflicts in the map file though almost every time. Fixing these conflicts is not hard to do but it is a pain as you'd have to do it locally and not by clicking a button in the UI. I can't think of a way around this if we want to keep the map files.

require('main.js').init()

Totally agree, this is much cleaner. It will also enable us to test with more flexibility as we won't have that pesky run() call at the end of certain files.

Changes made include:

• Compile all code to a single file that contains logical entrypoints to all of the actions. The physical entrypoint to each action is then a very simple file that calls into this single compiled file.
• Don't minimise the generated javascript, to avoid getting conflicts on every single change. I worry it will probably still happen because the map file is all on one line, but we could try it and see how bad it is.

I think I've addressed all comments and this is ready for a proper review and discussion again.

So far I think the only outstanding negative point is that we'll likely get conflicts on every code change that will require running commands locally to fix.

I'm going to close this issue as there isn't enough support to follow through on this and outweigh the downsides.
If we decide we want to do this in the future then this PR will still be here if we want to use it as a starting point.