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A collection of extensions for packwerk packages.



 Project Readme


packwerk-extensions is a home for checker extensions for packwerk 3.

Currently, it ships the following checkers to help improve the boundaries between packages. These checkers are:

  • A privacy checker that ensures other packages are using your package's public API
  • A visibility checker that allows packages to be private except to an explicit group of other packages.
  • A folder_visibility checker that allows packages to their sibling packs and parent pack (to be used in an application that uses folder packs)
  • A layer (formerly architecture) checker that allows packages to specify their "layer" and requires that each layer only communicate with layers below it.


Add packwerk-extensions to your Gemfile.

To register all checkers included in this gem, add the following to your packwerk.yml:

  - packwerk-extensions

Alternatively, you can require individual checkers:

  - packwerk/privacy/checker
  - packwerk/visibility/checker
  - packwerk/folder_visibility/checker
  - packwerk/layer/checker

Privacy Checker

The privacy checker extension was originally extracted from packwerk.

A package's privacy boundary is violated when there is a reference to the package's private constants from a source outside the package.

To enforce privacy for your package, set enforce_privacy to true or strict on your pack:

# components/merchandising/package.yml
enforce_privacy: true

Setting enforce_privacy to true will make all references to private constants in your package a violation.

Setting enforce_privacy to strict will forbid all references to private constants in your package. This includes violations that have been added to other packages' package_todo.yml files.

Note: You will need to remove all existing privacy violations before setting enforce_privacy to strict.

Using public folders

You may enforce privacy either way mentioned above and still expose a public API for your package by placing constants in the public folder, which by default is app/public. The constants in the public folder will be made available for use by the rest of the application.

Defining your own public folder

You may prefer to override the default public folder, you can do so on a per-package basis by defining a public_path.


public_path: my/custom/path/

Defining public constants through sigil


This way of of defining the public API of a package should be considered WIP. It is not supported by all tooling in the RubyAtScale ecosystem, as @alexevanczuk pointed out in a comment on the PR:

There are a couple of other places that will require changes related to this sigil. Namely, everything that is coupled to the public folder implementation of privacy.

In the rubyatscale org:

You may make individual files public within a private package by usage of a comment within the first 5 lines of the .rb file containing pack_public: true.


# pack_public: true
module Foo
  class Update

Now Foo::Update is considered public even though the foo package might be set to enforce_privacy: (true || strict).

It's important to note that when combining public_api: true with the declaration of private_constants, packwerk validate will raise an exception if both are used for the same constant. This must be resolved by removing the sigil from the .rb file or removing the constant from the list of private_constants.

If you are using rubocop, it may be configured in such a way that there must be an empty line after the magic keywords at the top of the file. Currently, this extension is not modifying rubocop in any way so it does not recognize pack_public: true as a valid magic keyword option. That means placing it at the end of the magic keywords will throw a rubocop exception. However, you can place it first in the list to avoid an exception in rubocop.

# typed: ignore
# frozen_string_literal: true
# pack_public: true

class Foo
end => Layout/EmptyLineAfterMagicComment: Add an empty line after magic comments.

# typed: ignore
# frozen_string_literal: true

# pack_public: true

class Foo
end => Less than ideal. This won't raise an issue in rubocop, however, only the first 5 lines are scanned for the magic comment of pack_public so there is risk at it being missed. It also is requiring extra empty lines in the group of magic comments.

# pack_public: true
# typed: ignore
# frozen_string_literal: true

class Foo
end => Ideal solution. No exceptions from rubocop and very low risk of the magic comment being out of range since

Using specific private constants

Sometimes it is desirable to only enforce privacy on a subset of constants in a package. You can do so by defining a private_constants list in your package.yml. Note that enforce_privacy must be set to true or 'strict' for this to work.

Ignore strict mode for violation coming from specific path patterns

If you want to activate 'strict' mode on your package but have a few privacy violations you know you will deal with later, you can set a list of patterns to exclude.

enforce_privacy: strict
- engines/another_engine/test/**/*

In this example, violations on constants of your engine referenced in those files engines/another_engine/test/**/* will not fail Packwerk checks.

Package Privacy violation

Packwerk thinks something is a privacy violation if you're referencing a constant, class, or module defined in the private implementation (i.e. not the public folder) of another package. We care about these because we want to make sure we only use parts of a package that have been exposed as public API.

Interpreting Privacy violation

/Users/JaneDoe/src/ Privacy violation: '::Billing::CarrierInvoiceTransaction' is private to 'billing' but referenced from 'user'. Is there a public entrypoint in 'billing/app/public/' that you can use instead?

Inference details: 'Billing::CarrierInvoiceTransaction' refers to ::Billing::CarrierInvoiceTransaction which seems to be defined in billing/app/models/billing/carrier_invoice_transaction.rb.

There has been a privacy violation of the package billing in the package user, through the use of the constant Billing::CarrierInvoiceTransaction in the file user/app/controllers/labels_controller.rb.


You may be accessing the implementation of a piece of functionality that is supposed to be accessed through a public interface on the package. Try to use the public interface instead. A package’s public interface should be defined in its app/public folder and documented.

The functionality you’re looking for may not be intended to be reused across packages at all. If there is no public interface for it but you have a good reason to use it from outside of its package, find the people responsible for the package and discuss a solution with them.

Visibility Checker

The visibility checker can be used to allow a package to be a private implementation detail of other packages.

To enforce visibility for your package, set enforce_visibility to true on your pack and specify visible_to for other packages that can use your package.

# components/merchandising/package.yml
enforce_visibility: true
  - components/other_package

Folder-Visibility Checker

The folder visibility checker can be used to allow a package to be private to their sibling packs and parent packs and will create todos if used by any other package.

To enforce visibility for your package, set enforce_folder_visibility to true on your pack.

# components/merchandising/package.yml
enforce_folder_visibility: true

Here is an example of paths and whether their use of packs/b/packs/e is OK or not, assuming that protects itself via enforce_folder_visibility

.                         OK (parent of parent)
packs/a                   VIOLATION
packs/b                   OK (parent)
packs/b/packs/d           OK (sibling)
packs/b/packs/e           ENFORCE_NESTED_VISIBILITY: TRUE
packs/b/packs/e/packs/f   VIOLATION
packs/b/packs/e/packs/g   VIOLATION
packs/b/packs/h           OK (sibling)
packs/c                   VIOLATION

Layer Checker

The layer checker can be used to enforce constraints on what can depend on what.

To enforce layers for your package, first define the layers in packwerk.yml, for example:

  - package
  - utility

Then, turn on the checker in your package:

# components/merchandising/package.yml
enforce_layers: true
layer: utility

Now this pack can only depend on other utility packages.

Deprecated Architecture Checker

The "Layer Checker" was formerly named "Architecture Checker". The associated keys were:

  • packwerk.yml architecture_layers, which is now layers
  • package.yml enforce_architecture, which is now enforce_layers
  • package.yml layer is still a valid key
  • package_todo.yml - architecture, which is now layer
  # script to migrate code from deprecated "architecture" violations to "layer" violations
  # sed and ripgrep required

  # replace 'architecture_layers' with 'layers' in packwerk.yml
  sed -i '' 's/architecture_layers/layers/g' ./packwerk.yml
  # replace 'enforce_architecture' with 'enforce_layers' in package.yml files
  `rg -l 'enforce_architecture' -g 'package.yml' | xargs sed -i '' 's,enforce_architecture,enforce_layers,g'`

  # replace '- architecture' with '- layer' in package_todo.yml files
  `rg -l 'architecture' -g 'package_todo.yml' | xargs sed -i '' 's/- architecture/- layer/g'`


Got another checker you would like to add? Add it to this repo!

Please ensure these commands pass for you locally:

srb tc
bin/rake test

Then, submit a PR!