[CI] Deduplicate actions/cache directives

[joshlf]

We have a generate_cache job in CI which pre-populates a cache that is re-used by other jobs:

zerocopy/.github/workflows/ci.yml

Lines 410 to 442 in 3bb9a54

	generate_cache:
	runs-on: ubuntu-latest
	name: Generate cache
	steps:
	- uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608 # v4.1.0
	- uses: actions/cache@v3
	with:
	path: |
	~/.cargo/
	key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.toml') }}
	- name: Populate cache
	run: |
	# Ensure all dependencies are downloaded - both for our crates and for
	# tools we use in CI. We don't care about these tools succeeding for
	# two reasons: First, this entire job is best-effort since it's just a
	# performance optimization. Second, there may be failures due to
	# issues other than failing to download dependencies (e.g., `cargo
	# metadata` called with a malformed `Cargo.toml`, build failure in our
	# own crate or in dependencies, etc). For those reasons, we discard
	# stderr and ignore status codes.
	#
	# For downloading our crates' dependencies in particular, note that
	# there is no support for doing this directly [1], so we just check
	# all crates using --tests.
	#
	# [1] https://stackoverflow.com/a/42139535/836390
	cargo check --workspace --tests &> /dev/null || true
	cargo metadata &> /dev/null || true
	cargo install cargo-readme --version 3.2.0 &> /dev/null || true
	cargo install --locked kani-verifier &> /dev/null || true
	cargo kani setup &> /dev/null || true

In each dependent job, we do the following:

• Use needs: generate_cache
• Use the following actions/cache action configuration:
  

  zerocopy/.github/workflows/ci.yml

  Lines 77 to 81 in 3bb9a54

  	- uses: actions/cache@v3
  	with:
  	path: |
  	~/.cargo/
  	key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.toml') }}

As of this writing, we copy that exact text five times. It'd be great if we could reduce the duplication.

Mentoring instructions

As proposed here by @mgeisler:

• Create a separate cache.yml file in .github/workflows

• Populate it with a job that performs these steps:

  zerocopy/.github/workflows/ci.yml

  Lines 77 to 81 in 3bb9a54

  	- uses: actions/cache@v3
  	with:
  	path: |
  	~/.cargo/
  	key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.toml') }}

• Replace uses of that pattern in ci.yml with an invocation of that file, ie:

  - name: Populate cache
    uses: `.github/workflows/cache.yml`

Old/obsolete mentoring instructions

As discussed in this StackOverflow comment,

You can extract your own actions: docs.github.com/en/actions/creating-actions. YAML's own support for this isn't available in GHA though: github.com/actions/runner/issues/1182.

The task is to figure out whether there's a way to use that technique to define a new action in ci.yml that we can re-use in other steps. If there's an easy, simple syntax for this, we should do it. If it would require a lot of complexity, then it's not worth it.

[zoo868e]

Hi @joshlf,
Is workflow_run what you're looking for?

[zoo868e]

I apologize for any inconvenience. It appears that the workflow_run isn't triggered when the Generate Cache Workflow is initiated by a pull request. Is it acceptable to employ the following workaround for this situation?

https://github.com/orgs/community/discussions/25220#discussioncomment-3246922

[joshlf]

I apologize for any inconvenience. It appears that the workflow_run isn't triggered when the Generate Cache Workflow is initiated by a pull request. Is it acceptable to employ the following workaround for this situation?

https://github.com/orgs/community/discussions/25220#discussioncomment-3246922

Thanks for finding that workaround! Honestly probably not worth the complexity given that this is a very minor problem to begin with. If there's no good solution, it's probably fine to just leave it as-is. I'm gonna close this, but feel free to comment if you figure something else out!

[mgeisler]

Would it perhaps be interesting to use a local action? I do that in Comprehensive Rust:

• .github/workflows/build.yml uses
• .github/workflows/setup-rust-cache/action.yml

This has worked out great for us in the last 12 months or so.

[joshlf]

Oh yeah that's perfect! I'll re-open the issue with that suggestion. Thanks, @mgeisler!

[Sh0g0-1758]

@joshlf , I have created a PR as a patch for this issue. Can you please review it and suggest changes in it if required.

[dorryspears]

@joshlf Hello, made a fix for this with #835. All tests pass
Happy weekend!