oRFC: 1 The Collective Code Construction Contract (C4)

The Collective Code Construction Contract (C4) is an evolution of the github.com Fork + Pull Model, aimed at providing an optimal collaboration model for free software projects. This is revision 1 of the C4 specification.




Jeremy Rossi <jeremy at jeremyrossi dot com>






The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119[#f1]_.


C4 is meant to provide a reusable optimal collaboration model for open source software projects. It has these specific goals:

  • To maximize the scale of the community around a project, by reducing the friction for new Contributors and creating a scaled participation model with strong positive feedbacks;

  • To relieve dependencies on key individuals by separating different skill sets so that there is a larger pool of competence in any required domain;

  • To allow the project to develop faster and more accurately, by increasing the diversity of the decision making process;

  • To support the natural life cycle of project versions from experimental through to stable, by allowing safe experimentation, rapid failure, and isolation of stable code;

  • To reduce the internal complexity of project repositories, thus making it easier for Contributors to participate and reducing the scope for error;

  • To enforce collective ownership of the project, which increases economic incentive to Contributors and reduces the risk of hijack by hostile entities.



  • The project SHALL use the git distributed revision control system.

  • The project SHALL be hosted on github.com or equivalent, herein called the “Platform”.

  • The project SHALL use the Platform issue tracker.

  • The project SHOULD have clearly documented guidelines for code style.

  • A “Contributor” is a person who wishes to provide a patch, being a set of commits that solve some clearly identified problem.

  • A “Maintainer” is a person who merge patches to the project. Maintainers are not developers; their job is to enforce process.

  • Contributors SHALL NOT have commit access to the repository unless they are also Maintainers.

  • Maintainers SHALL have commit access to the repository.

  • Everyone, without distinction or discrimination, SHALL have an equal right to become a Contributor under the terms of this contract.

Licensing and Ownership

  • The project SHALL use the GPLv2 or a variant thereof (LGPL, AGPL).

  • All contributions to the project source code (“patches”) SHALL use the same license as the project.

  • All patches are owned by their authors. There SHALL NOT be any copyright assignment process.

  • The copyrights in the project SHALL be owned collectively by all its Contributors.

  • Each Contributor SHALL be responsible for identifying themselves in the project Contributor list.

Patch Requirements

  • Maintainers and Contributors MUST have a Platform account and SHOULD use their real names or a well-known alias.

  • A patch SHOULD be a minimal and accurate answer to exactly one identified and agreed problem.

  • A patch MUST adhere to the code style guidelines of the project if these are defined.

  • A patch MUST adhere to the “Evolution of Public Contracts” guidelines defined below.

  • A patch SHALL NOT include non-trivial code from other projects unless the Contributor is the original author of that code.

  • A patch MUST compile cleanly and pass project self-tests on at least the principle target platform.

  • A patch commit message SHOULD consist of a single short (less than 50 character) line summarizing the change, optionally followed by a blank line and then a more thorough description.

  • A “Correct Patch” is one that satisfies the above requirements.

Development Process

  • Change on the project SHALL be governed by the pattern of accurately identifying problems and applying minimal, accurate solutions to these problems.

  • To initiate changes, a user SHOULD log an issue on the project Platform issue tracker.

  • The user SHOULD write the issue by describing the problem they face or observe.

  • The user SHOULD seek consensus on the accuracy of their observation, and the value of solving the problem.

  • Users SHALL NOT log feature requests, ideas, suggestions, or any solutions to problems that are not explicitly documented and provable.

  • Thus, the release history of the project SHALL be a list of meaningful issues logged and solved.

  • To work on an issue, a Contributor SHALL fork the project repository and then work on their forked repository.

  • To submit a patch, a Contributor SHALL create a Platform pull request back to the project.

  • A Contributor SHALL NOT commit changes directly to the project.

  • To discuss a patch, people MAY comment on the Platform pull request, on the commit, or elsewhere.

  • To accept or reject a patch, a Maintainer SHALL use the Platform interface.

  • Maintainers SHALL NOT accept their own patches.

  • Maintainers SHALL NOT make value judgments on correct patches.

  • Maintainers SHALL merge correct patches rapidly.

  • The Contributor MAY tag an issue as “Ready” after making a pull request for the issue.

  • The user who created an issue SHOULD close the issue after checking the patch is successful.

  • Maintainers SHOULD ask for improvements to incorrect patches and SHOULD reject incorrect patches if the Contributor does not respond constructively.

  • Any Contributor who has value judgments on a correct patch SHOULD express these via their own patches.

  • Maintainers MAY commit changes to non-source documentation directly to the project.

Creating Stable Releases

  • The project SHALL have one branch (“master”) that always holds the latest in-progress version and SHOULD always build.

  • The project SHALL NOT use topic branches for any reason. Personal forks MAY use topic branches.

  • To make a stable release someone SHALL fork the repository by copying it and thus become maintainer of this repository.

  • Forking a project for stabilization MAY be done unilaterally and without agreement of project maintainers.

  • A stabilization project SHOULD be maintained by the same process as the main project.

  • A patch to a stabilization project declared “stable” SHALL be accompanied by a reproducible test case.

Evolution of Public Contracts

  • All Public Contracts (APIs or protocols) SHOULD be documented.

  • All Public Contracts SHOULD have space for extensibility and experimentation.

  • A patch that modifies a stable Public Contract SHOULD not break existing applications unless there is overriding consensus on the value of doing this.

  • A patch that introduces new features to a Public Contract SHOULD do so using new names.

  • Old names SHOULD be deprecated in a systematic fashion by marking new names as “experimental” until they are stable, then marking the old names as “deprecated”.

  • When sufficient time has passed, old deprecated names SHOULD be marked “legacy” and eventually removed.

  • Old names SHALL NOT be reused by new features.

  • When old names are removed, their implementations MUST provoke an exception (assertion) if used by applications.

Project Administration

  • The project founders SHALL act as Administrators to manage the set of project Maintainers.

  • The Administrators SHALL ensure their own succession over time by promoting the most effective Maintainers.

  • A new Contributor who makes a correct patch SHALL be invited to become a Maintainer.

  • Administrators MAY remove Maintainers who are inactive for an extended period of time, or who repeatedly fail to apply this process accurately.

Further Reading

  • Argyris’ Models 1 and 2 - the goals of C4.1 are consistent with Argyris’ Model 2.

  • Toyota Kata - covering the Improvement Kata (fixing problems one at a time) and the Coaching Kata (helping others to learn the Improvement Kata).



“Key words for use in RFCs to Indicate Requirement Levels” - http://tools.ietf.org/html/rfc2119


“Definition of a Free and Open Standard” - http://www.digistan.org/open-standard:definition


“Consensus Oriented Specification System” - http://www.digistan.org/spec:1/COSS


Original content licensed under the Creative Commons Attribution-Share Alike 3.0 License. (c) Copyright (c) 2007-2011 iMatix Corporation and Contributors.