1/C4.1 - Collective Code Construction Contract

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



Forked from



Jim Garlick <garlick@llnl.gov>




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.


C4.1 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 a share-alike license, such as the GPLv3 or a variant thereof (LGPL, AGPL), or the MPLv2 for reasons outlined in RFC 2.

  • 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.

  • The git commit history SHALL be considered the primary source of contributor identities.

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 defined in RFC 7.

  • 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 MUST be accompanied by a commit message.

  • A commit message SHOULD consist of a title (50 characters or less) summarizing the change, optionally followed by a blank line and a message body.

  • A commit message SHOULD be written in the imperative (Fixes or Fix).

  • A commit message title MAY denote the section of code being changed with a tag followed by a single colon, e.g. name: short description.

  • A commit message title SHOULD NOT include a period.

  • A commit message body SHOULD be wrapped at 72 characters, with the exception of non-prose lines like list items, quoted text, or quotes from other commits.

  • A commit message body SHOULD include a description of the change being made and its reason and/or purpose.

  • Where applicable, a commit message body SHOULD reference an Issue by number (e.g. Fixes #33”).

  • A commit message body SHOULD begin with Problem: and a short paragraph describing the problem solved by the commit. Even commits that add features MAY include such a problem statement.

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

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

  • The user or Contributor 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.

  • If the Platform implements pull requests as issues, a Contributor MAY directly send a pull request without logging a separate issue.

  • 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 SHOULD NOT merge their own patches except in exceptional cases, such as non-responsiveness from other Maintainers for an extended period (more than 1-2 days).

  • Maintainers SHALL NOT make value judgments on correct patches.

  • Maintainers SHALL merge correct patches from other Contributors 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.

  • Autotools products, if applicable, SHOULD NOT be checked into the project revision control system

Release Process

  • Releases SHALL be tagged with git annotated tags.

  • Release names SHALL employ version numbers that follow the Semantic Versioning 2.0.0 standard, (C.f. https://semver.org).

  • Release materials for projects that use GNU Autotools SHOULD include “dist tarballs”; that is, a source distribution with pre-generated configure script, Makefile.in, etc..

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