Add root_path attribute for directory crate roots#4142
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Allows specifying `root_path` when `root` (`crate_root` or `srcs` entrypoint) is a directory artifact (`TreeArtifact`). This enables rules_rust targets (`rust_library`, `rust_binary`, `rust_test`, etc.) to consume directory artifacts produced by upstream rules and correctly construct the path to the crate root (`lib.rs` / `main.rs`). * Adds `root_path` attribute to `_COMMON_ATTRS` and `CrateInfo` provider. * Updates `rustc_compile_action` argument construction (`rustc.bzl`) to join `crate_info.root.path` with `root_path` when `crate_info.root.is_directory` is true. * Adds a unit and build test case under `test/root_path/` using a custom rule that packages its `srcs` as a directory artifact (`TreeArtifact`) and compiles a `rust_library` and `rust_test` from it.
…_rust into jul26-root-path
krasimirgg
marked this pull request as ready for review
July 9, 2026 12:49
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Allows specifying
root_pathwhen the crate root (srcsentrypoint) is a directory artifact (TreeArtifact). This enables rules_rust targets (rust_library,rust_binary,rust_test, etc.) to consume directory artifacts produced by upstream rules and correctly construct the path to the crate root (lib.rs/main.rs).We use something like this internally to build standard libraries from sources distributed as .zip source archives: a custom rule extracts the contents into a generated directory artifact, which then the rust rules can consume as sources.
This may be helpful to achieve the request from #3757, where the user is trying to consume a directory of generated sources.
root_pathattribute to_COMMON_ATTRSandCrateInfoprovider.rustc_compile_actionargument construction (rustc.bzl) to joincrate_info.root.pathwithroot_pathwhencrate_info.root.is_directoryis true.test/root_path/using a custom rule that packages itssrcsas a directory artifact (TreeArtifact) and compiles arust_libraryandrust_testfrom it.I have taken special care in the rustc argument construction to ensure it is compatible with the new bazel path remapping guidelines.
While here, added a few checks in the rules for combinations of
srcs,crateandcrate_rootattributes that don't make sense and would cause compilation to fail later anyways.