Migrating from good-fences

good-fences segments a TypeScript project into areas and controls what each can import, using fence.json files. rev-dep expresses the same boundaries as central module boundaries and restricted imports checks.

Why migrate

• Speed. rev-dep is Go-based and runs in a single parallel pass - faster on large codebases.
• One config, more checks. good-fences only does boundaries. rev-dep enforces boundaries and detects circular imports, unused exports, unused/missing dependencies, and more.

What carries over, what changes

• Covered well: controlling which areas may import which, and which npm dependencies an area may use.
• Different model. good-fences uses tags and per-directory fence.json files; rev-dep uses path patterns in one central config. You express the same intent ("UI may not import API") as a path-pattern boundary instead of tagging directories.
• No per-directory files. Boundaries live in rev-dep.config.jsonc, not scattered fence.json files - simpler to review, but a different workflow.

Feature mapping

good-fences (fence.json)	rev-dep
tags + imports (which tags may be imported)	moduleBoundaries (pattern + allow / deny)
exports (accessibleTo) - who may import this area	moduleBoundaries / restrictedImportsDetection
dependencies (allowed npm packages)	restrictedImportsDetection (denyModules)
-	circular, unused exports, unused/missing dependencies, conventions

Translating your config

A fence.json in src/ui that may only be imported by app and forbids importing api:

{
  "tags": ["ui"],
  "exports": [{ "modules": "*", "accessibleTo": ["app"] }],
  "imports": ["ui", "shared"]
}

becomes a path-pattern boundary in rev-dep.config.jsonc:

{
  "rules": [
    {
      "path": ".",
      "moduleBoundaries": [
        {
          "name": "ui-imports",
          "pattern": "src/ui/**",
          "allow": ["src/ui/**", "src/shared/**"]
        },
        {
          "name": "only-app-imports-ui",
          "pattern": "src/!(app|ui)/**",
          "deny": ["src/ui/**"]
        }
      ]
    }
  ]
}

To restrict which npm packages an area may import (good-fences dependencies), use restrictedImportsDetection with denyModules.

Running it

# good-fences
npx gf

# rev-dep
rev-dep config run

Next steps

• Module boundaries - the core mapping for fences.
• Monorepo integration guide.