Add a workflow to build and upload the runner

[robertbrignull]

Instead of building the runner locally we should probably standardise on building it within actions to get a consistent environment. This PR introduces a workflow that just builds the runner and upload the artefacts.

I'm intending this currently state as just a starting point. A couple of open questions I have are:

• Should this run on push or just workflow_dispatch? I only added push so I could test it before merging to the default branch.
• Should we merge this with split.yml? The primary use case for this is when doing a release, but it could be useful to be able to run separatetly too.

@rneatherway

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Confirm the readme has been updated if necessary.

[rneatherway]

I suggest just using workflow_dispatch and adding the ability for it to upload the artefacts directly to the specified release like this:

codeql-action/.github/workflows/split.yml

Lines 65 to 73 in ffaa8aa

	- name: Upload Platform Package
	uses: actions/upload-release-asset@v1
	env:
	GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
	with:
	upload_url: ${{ steps.save_url.outputs.upload_url }}
	asset_path: ./codeql-bundle-${{matrix.platform}}.tar.gz
	asset_name: codeql-bundle-${{matrix.platform}}.tar.gz
	asset_content_type: application/tar+gzip

Keep it separate though as split.yml will be able to go away when we start preparing those platform-specific bundles ahead of time.

[rneatherway]

I've tested this using the on: push trigger and a hardcoded RELEASE_TAG, which I then removed in the last commit.

• https://github.com/github/codeql-action/actions/runs/317389622
• https://github.com/github/codeql-action/releases/tag/test-build-runner

Once this is merged I will delete the test release.

[chrisgavin]

One small change, but otherwise it looks good to me.

[chrisgavin]

Suggested change

	- uses: actions/checkout@v2
	- uses: actions/checkout@v2
	with:
	ref: refs/tags/${{ github.event.inputs.bundle-tag }}

It's potentially confusing to build the code from main and upload it as an artifact on a tagged release.

(It would be nice if we could just use the workflow from the release tag too, but workflows can't be dispatched on tags currently.)

[rneatherway]

I've followed Robert's suggestion to make the bundle-tag optional, which now makes this a bit awkward. Do you see a way apart from having two calls to actions/checkout@2 each with an if?

[rneatherway]

In the interests of getting a version of this ready I am going to merge. We can later update this if we see a way to resolve the inconsistency.

[robertbrignull]

Thanks for taking on the rest of this @rneatherway.