Build-system-aware cross-repo validation (Bazel, Nix)

[avrabe]

Context

Cross-repo traceability validation (REQ-020) currently requires manually declaring externals in rivet.yaml. But projects using Bazel or Nix already have a dependency graph with pinned revisions — rivet should be able to read it directly.

Eclipse SCORE pins 75+ repos via known_good.json → auto-generated MODULE.bazel with git_override(). Nix flakes pin inputs in flake.lock. Both contain exactly the information rivet needs: which repos, at what commits.

Problem

Maintaining a parallel dependency declaration in rivet.yaml:

1. Drifts from the build system's source of truth
2. Requires manual updates when repos are added/removed
3. Forces teams to learn rivet-specific config when they already express this in Bazel/Nix

Proposed approach

Build system discovery

Rivet auto-discovers cross-repo dependencies from build system manifests:

# rivet.yaml
externals:
  discovery: bazel  # or: nix, known-good-json, manual (default)
  # Optional overrides still allowed
  overrides:
    score-baselibs:
      artifacts-path: docs/requirements

Bazel provider: Parse MODULE.bazel for bazel_dep() + git_override() entries. Resolve workspace paths via bazel info output_base or read MODULE.bazel.lock.

Nix provider: Parse flake.lock for input entries with locked.rev and locked.url.

known-good-json provider: Parse SCORE-style known_good.json with repo names, commit SHAs, and code roots.

Rivet as a Bazel rule / Nix derivation

Additionally, rivet itself should be consumable as:

• rules_rivet: Bazel module with a rivet_validate() rule that runs validation as a bazel test target
• Nix flake: nix run github:pulseengine/rivet -- validate
• Both distribute the single static binary without pulling LLVM/JDK/Python

Rivet artifacts

• REQ-027
• DD-022
• FEAT-044, FEAT-045

References

• SCORE's known_good.json: eclipse-score/reference_integration
• SCORE's MODULE.bazel composition: auto-generated from known_good.json
• SCORE disk space issue: Docs-as-code module build takes up too much disk space eclipse-score/docs-as-code#339
• Existing cross-repo linking: REQ-020, DD-014..DD-017, FEAT-033..FEAT-039

[avrabe]

Implemented: FEAT-044 (providers.rs), FEAT-046 (bazel.rs parser), FEAT-045 (rules_rivet + Nix flake). Shipped in v0.1.0.