How do I use Runfiles with rust?

[SvenFinn]

Hi everyone,

I’m working on Rust integration tests using Bazel with rules_rust. I want my tests to read some test data files at runtime, and ideally, they should also work when running via cargo test.

I’ve seen references to a runfiles crate, but the documentation is scarce and a bit confusing. Specifically:

• How do I properly use Runfiles in a Rust test under Bazel?
• Do I need to add anything to Cargo.toml or the BUILD.bazel file?
• How can I make the test code compatible with both Bazel and Cargo?

Thanks!

[illicitonion]

You can find runfiles examples in https://github.com/bazelbuild/rules_rust/blob/main/examples/runfiles/pkg_b/src/lib.rs - for Bazel, you need to add a dependency on @rules_rust//rust/runfiles

Unfortunately making both work out of the box is non-trivial. You probably want to root your runfiles in a child of your $CARGO_MANIFEST_DIR, conditionally sniff for if you're building with Bazel, with use either the runfiles mechanism above of a path relative to $CARGO_MANIFEST_DIR depending.