bazel-differrous

Rust rewrite of Tinder's bazel-diff, designed as a drop-in CLI and output compatible replacement with faster, traced, async execution and first-class Bazel 8/9 bzlmod support.

Highlights

• Drop-in compatibility: generate-hashes and get-impacted-targets match the upstream jar byte-for-byte on WORKSPACE and MODULE.bazel fixtures, including fine-grained external repo hashing and dep-edges output.
• Bzlmod ready: canonical repo names with trailing + are preserved, @@ labels hash identically to upstream, and pure bzlmod workspaces (no //external) are handled.
• Modern Rust pipeline: async Bazel invocations, streamed proto decoding, deterministic hashing, structured tracing output, and optional verbose logging via -v/RUST_LOG.
• Tests and tooling: nearly 600 Rust tests plus a parity harness against the upstream jar, cargo-nextest with timeouts (nextest.toml), and GitHub Actions validated with act.

Quick start

just build            # cargo build --workspace
just nextest          # runs the full suite with timeouts
just build-upstream-bazel-diff
just integration-tests

• The upstream jar lives at target/upstream/bazel-diff_deploy.jar and is built from the vendor/bazel-diff submodule. just build-upstream-bazel-diff automates this.
• Local CI: just act-ci (uses the ghcr.io/catthehacker/ubuntu:act-latest image; set --container-architecture linux/amd64 on Apple silicon).
• No system protoc is required; the prost build uses protoc-bin-vendored during compilation.

CLI usage

generate-hashes

bazel-differrous generate-hashes \
  -w /path/to/workspace \
  --bazelPath bazelisk \
  --bazelCommandOptions=--enable_workspace \
  --includeTargetType \
  --fineGrainedHashExternalRepos @@depmod \
  --contentHashPath content_hashes.json \
  --seed-filepaths seed_files.txt \
  --modified-filepaths modified_files.txt \
  -d dep_edges.json > hashes.json

• Supports --useCquery, --excludeExternalTargets, --ignoredRuleHashingAttributes, --fineGrainedHashExternalRepos[File], --seed-filepaths, --contentHashPath, --modified-filepaths, and --targetType/-tt exactly like the Java tool.
• Outputs hash JSON (and optional dep-edges JSON) identically to bazel-diff for both legacy WORKSPACE and bzlmod projects.

get-impacted-targets

bazel-differrous get-impacted-targets \
  -sh starting.json -fh final.json \
  [-d dep_edges.json] \
  [--targetType Rule,SourceFile] \
  [-o impacted.json]

• Without -d, emits newline labels; with dep-edges it emits JSON with distance metrics, matching upstream ordering and exit codes.

Testing and verification

• cargo nextest run --workspace exercises ~600 unit/property tests (label normalization, hashing edge cases, bzlmod canonical names) plus integration tests; timeouts are configured in nextest.toml.
• Parity harness (crates/integration-tests) runs the Rust CLI and the upstream jar with identical flags and compares stdout/stderr/exit codes byte-for-byte on WORKSPACE and MODULE fixtures. Tests skip automatically if the jar is absent.
• GitHub Actions workflow .github/workflows/ci.yml mirrors the Justfile targets and is validated locally with act.

Observability and profiling

• -v or RUST_LOG=debug enables detailed tracing spans; outputs remain stable for parity tests.
• Binaries are compatible with standard profilers (perf, cargo flamegraph, tokio-console) without rebuild flags.

Project layout

• crates/core: hashing engine, Bazel adapters, impact diff logic, and label/attribute normalization.
• crates/cli: Clap-based CLI wiring, tracing init, and file I/O.
• crates/proto: prost-generated Bazel streamed proto types.
• crates/integration-tests: parity harness and fixtures.
• tests/fixtures + tests/golden: shared fixtures and captured upstream outputs.
• vendor/bazel-diff: upstream submodule used for goldens and behavioral reference.

Credits

This project builds directly on the ideas and formats from the upstream bazel-diff authors at Tinder/Match Group and the wider Bazel community. See CREDITS.md for acknowledgements and licensing details.