16/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. C4 is derived from the ZeroMQ contribution policy of early 2012.

  • Name: rfc.zeromq.org/spec:16/C4
  • Editor: Pieter Hintjens <moc.xitami|hp#moc.xitami|hp>

Note: this RFC is superceded by rfc.zeromq.org/spec:22/C4.1.

Language

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[1].

Goals

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.

Design

Preliminaries

  • 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 GPLv3 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 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 on at least the most important target platforms.
  • 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 SHALL 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.
  • Maintainers of the stabilization project SHALL maintain it through pull requests which MAY cherry-pick patches from the forked project.
  • A patch to a repository declared "stable" SHALL be accompanied by a reproducible test case.
  • A stabilization repository SHOULD progress through these phases: "unstable", "candidate", "stable", and then "legacy". That is, the default behavior of stabilization repositories is to die.

Evolution of Public Contracts

  • All Public Contracts (APIs or protocols) SHOULD be documented.
  • All Public Contracts SHALL use Semantic Versioning[4].
  • All Public Contracts SHOULD have space for extensibility and experimentation.
  • A patch that modifies a Public Contract SHOULD not break existing applications unless there is prior 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.

References

Bibliography
1. "Key words for use in RFCs to Indicate Requirement Levels" - ietf.org
2. "Definition of a Free and Open Standard" - digistan.org
3. "Consensus Oriented Specification System" - digistan.org
4. "Semantic Versioning 2.0.0-rc.1" - semver.org

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