continuous integration assets look odd

[raulk]

The CI pipeline is producing a bundle that's 235MiB in size. After the latest changes to the bundling logic, we're probably publishing the wrong root directory.

https://github.com/filecoin-project/builtin-actors/actions/runs/2083018859

[raulk]

It contains the bundles from various builds. This is probably related to two facts:

1. The OUT_DIR fed to the build script is hash-based and not known outside the build. Thus the CI job is publishing the root output directory.
2. We are caching the output directory, and the caches are bleeding over between CI builds, thus leading to the accumulation.

[raulk]

Documenting potential solutions after a short investigation.

1. Bite the bullet and avoid emitting artifacts on OUT_DIR directly (randomized), but some predictable parent of that.
2. Pass an explicit OUT_DIR through --out-dir.
   • Requires Rust nightly and enabling unstable Cargo features.
   • Tried this locally and I didn't get it to work.
3. Use cargo build --build-plan to determine the OUT_DIR ahead of time.
   • This is what IntelliJ Rust was using: cargo metadata: get build script OUT_DIR rust-lang/cargo#7546 (comment).
   • However, this is going to be deprecated, so a non-starter.
   • Should build-plans be deleted? rust-lang/cargo#7614
4. Use cargo build --message-format=json.
   • This PR added support for outputting the out_dir there: Add value OUT_DIR to build-script-executed JSON message rust-lang/cargo#7622
   • It will require quite a bit of output parsing to identify the right trace/line (see below).
5. Capture the out_dir we emit as a cargo:warning.

I guess (4) would be the recommended way, but it feels a bit complex and rather dependent on Cargo tooling breakages/decisions. (5) seems to be the most decoupled and future-proof way.

Proposed solution is to add a bundle $path Makefile target that builds teeing the output into a tmp file. It then grepts it to find the out_dir and copies the bundle from within to $path.

---

cargo build --message-format=json trace containing the out_dir (cherry-picked from other traces + normal output):

{
	"reason": "build-script-executed",
	"package_id": "fil_builtin_actors_bundle 7.0.5-alpha.1 (path+file:///Users/raul/W/pl/canonical-actors)",
	"linked_libs": [],
	"linked_paths": [],
	"cfgs": [],
	"env": [],
	"out_dir": "/Users/raul/W/pl/canonical-actors/target/debug/build/fil_builtin_actors_bundle-81ea31c1db216196/out"
}

[vmx]

6. Let the build.rs write a file called out.dir into the CARGO_MANIFEST_DIR which contains the value of OUT_DIR.