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  1. Contributing to Bitcoin Core
  2. ============================
  3. The Bitcoin Core project operates an open contributor model where anyone is
  4. welcome to contribute towards development in the form of peer review, testing
  5. and patches. This document explains the practical process and guidelines for
  6. contributing.
  7. Firstly in terms of structure, there is no particular concept of "Core
  8. developers" in the sense of privileged people. Open source often naturally
  9. revolves around meritocracy where longer term contributors gain more trust from
  10. the developer community. However, some hierarchy is necessary for practical
  11. purposes. As such there are repository "maintainers" who are responsible for
  12. merging pull requests as well as a "lead maintainer" who is responsible for the
  13. release cycle, overall merging, moderation and appointment of maintainers.
  14. Contributor Workflow
  15. --------------------
  16. The codebase is maintained using the "contributor workflow" where everyone
  17. without exception contributes patch proposals using "pull requests". This
  18. facilitates social contribution, easy testing and peer review.
  19. To contribute a patch, the workflow is as follows:
  20. - Fork repository
  21. - Create topic branch
  22. - Commit patches
  23. The project coding conventions in the [developer notes](doc/
  24. must be adhered to.
  25. In general [commits should be atomic](
  26. and diffs should be easy to read. For this reason do not mix any formatting
  27. fixes or code moves with actual code changes.
  28. Commit messages should be verbose by default consisting of a short subject line
  29. (50 chars max), a blank line and detailed explanatory text as separate
  30. paragraph(s), unless the title alone is self-explanatory (like "Corrected typo
  31. in init.cpp") in which case a single title line is sufficient. Commit messages should be
  32. helpful to people reading your code in the future, so explain the reasoning for
  33. your decisions. Further explanation [here](
  34. If a particular commit references another issue, please add the reference, for
  35. example `refs #1234`, or `fixes #4321`. Using the `fixes` or `closes` keywords
  36. will cause the corresponding issue to be closed when the pull request is merged.
  37. Please refer to the [Git manual]( for more information
  38. about Git.
  39. - Push changes to your fork
  40. - Create pull request
  41. The title of the pull request should be prefixed by the component or area that
  42. the pull request affects. Valid areas as:
  43. - *Consensus* for changes to consensus critical code
  44. - *Docs* for changes to the documentation
  45. - *Qt* for changes to bitcoin-qt
  46. - *Mining* for changes to the mining code
  47. - *Net* or *P2P* for changes to the peer-to-peer network code
  48. - *RPC/REST/ZMQ* for changes to the RPC, REST or ZMQ APIs
  49. - *Scripts and tools* for changes to the scripts and tools
  50. - *Tests* for changes to the bitcoin unit tests or QA tests
  51. - *Trivial* should **only** be used for PRs that do not change generated
  52. executable code. Notably, refactors (change of function arguments and code
  53. reorganization) and changes in behavior should **not** be marked as trivial.
  54. Examples of trivial PRs are changes to:
  55. - comments
  56. - whitespace
  57. - variable names
  58. - logging and messages
  59. - *Utils and libraries* for changes to the utils and libraries
  60. - *Wallet* for changes to the wallet code
  61. Examples:
  62. Consensus: Add new opcode for BIP-XXXX OP_CHECKAWESOMESIG
  63. Net: Automatically create hidden service, listen on Tor
  64. Qt: Add feed bump button
  65. Trivial: Fix typo in init.cpp
  66. If a pull request is specifically not to be considered for merging (yet) please
  67. prefix the title with [WIP] or use [Tasks Lists](
  68. in the body of the pull request to indicate tasks are pending.
  69. The body of the pull request should contain enough description about what the
  70. patch does together with any justification/reasoning. You should include
  71. references to any discussions (for example other tickets or mailing list
  72. discussions).
  73. At this stage one should expect comments and review from other contributors. You
  74. can add more commits to your pull request by committing them locally and pushing
  75. to your fork until you have satisfied all feedback.
  76. Squashing Commits
  77. ---------------------------
  78. If your pull request is accepted for merging, you may be asked by a maintainer
  79. to squash and or [rebase]( your commits
  80. before it will be merged. The basic squashing workflow is shown below.
  81. git checkout your_branch_name
  82. git rebase -i HEAD~n
  83. # n is normally the number of commits in the pull
  84. # set commits from 'pick' to 'squash', save and quit
  85. # on the next screen, edit/refine commit messages
  86. # save and quit
  87. git push -f # (force push to GitHub)
  88. If you have problems with squashing (or other workflows with `git`), you can
  89. alternatively enable "Allow edits from maintainers" in the right GitHub
  90. sidebar and ask for help in the pull request.
  91. Please refrain from creating several pull requests for the same change.
  92. Use the pull request that is already open (or was created earlier) to amend
  93. changes. This preserves the discussion and review that happened earlier for
  94. the respective change set.
  95. The length of time required for peer review is unpredictable and will vary from
  96. pull request to pull request.
  97. Pull Request Philosophy
  98. -----------------------
  99. Patchsets should always be focused. For example, a pull request could add a
  100. feature, fix a bug, or refactor code; but not a mixture. Please also avoid super
  101. pull requests which attempt to do too much, are overly large, or overly complex
  102. as this makes review difficult.
  103. ### Features
  104. When adding a new feature, thought must be given to the long term technical debt
  105. and maintenance that feature may require after inclusion. Before proposing a new
  106. feature that will require maintenance, please consider if you are willing to
  107. maintain it (including bug fixing). If features get orphaned with no maintainer
  108. in the future, they may be removed by the Repository Maintainer.
  109. ### Refactoring
  110. Refactoring is a necessary part of any software project's evolution. The
  111. following guidelines cover refactoring pull requests for the project.
  112. There are three categories of refactoring, code only moves, code style fixes,
  113. code refactoring. In general refactoring pull requests should not mix these
  114. three kinds of activity in order to make refactoring pull requests easy to
  115. review and uncontroversial. In all cases, refactoring PRs must not change the
  116. behaviour of code within the pull request (bugs must be preserved as is).
  117. Project maintainers aim for a quick turnaround on refactoring pull requests, so
  118. where possible keep them short, uncomplex and easy to verify.
  119. "Decision Making" Process
  120. -------------------------
  121. The following applies to code changes to the Bitcoin Core project (and related
  122. projects such as libsecp256k1), and is not to be confused with overall Bitcoin
  123. Network Protocol consensus changes.
  124. Whether a pull request is merged into Bitcoin Core rests with the project merge
  125. maintainers and ultimately the project lead.
  126. Maintainers will take into consideration if a patch is in line with the general
  127. principles of the project; meets the minimum standards for inclusion; and will
  128. judge the general consensus of contributors.
  129. In general, all pull requests must:
  130. - have a clear use case, fix a demonstrable bug or serve the greater good of
  131. the project (for example refactoring for modularisation);
  132. - be well peer reviewed;
  133. - have unit tests and functional tests where appropriate;
  134. - follow code style guidelines;
  135. - not break the existing test suite;
  136. - where bugs are fixed, where possible, there should be unit tests
  137. demonstrating the bug and also proving the fix. This helps prevent regression.
  138. Patches that change Bitcoin consensus rules are considerably more involved than
  139. normal because they affect the entire ecosystem and so must be preceded by
  140. extensive mailing list discussions and have a numbered BIP. While each case will
  141. be different, one should be prepared to expend more time and effort than for
  142. other kinds of patches because of increased peer review and consensus building
  143. requirements.
  144. ### Peer Review
  145. Anyone may participate in peer review which is expressed by comments in the pull
  146. request. Typically reviewers will review the code for obvious errors, as well as
  147. test out the patch set and opine on the technical merits of the patch. Project
  148. maintainers take into account the peer review when determining if there is
  149. consensus to merge a pull request (remember that discussions may have been
  150. spread out over GitHub, mailing list and IRC discussions). The following
  151. language is used within pull-request comments:
  152. - ACK means "I have tested the code and I agree it should be merged";
  153. - NACK means "I disagree this should be merged", and must be accompanied by
  154. sound technical justification (or in certain cases of copyright/patent/licensing
  155. issues, legal justification). NACKs without accompanying reasoning may be
  156. disregarded;
  157. - utACK means "I have not tested the code, but I have reviewed it and it looks
  158. OK, I agree it can be merged";
  159. - Concept ACK means "I agree in the general principle of this pull request";
  160. - Nit refers to trivial, often non-blocking issues.
  161. Reviewers should include the commit hash which they reviewed in their comments.
  162. Project maintainers reserve the right to weigh the opinions of peer reviewers
  163. using common sense judgement and also may weight based on meritocracy: Those
  164. that have demonstrated a deeper commitment and understanding towards the project
  165. (over time) or have clear domain expertise may naturally have more weight, as
  166. one would expect in all walks of life.
  167. Where a patch set affects consensus critical code, the bar will be set much
  168. higher in terms of discussion and peer review requirements, keeping in mind that
  169. mistakes could be very costly to the wider community. This includes refactoring
  170. of consensus critical code.
  171. Where a patch set proposes to change the Bitcoin consensus, it must have been
  172. discussed extensively on the mailing list and IRC, be accompanied by a widely
  173. discussed BIP and have a generally widely perceived technical consensus of being
  174. a worthwhile change based on the judgement of the maintainers.
  175. ### Finding Reviewers
  176. As most reviewers are themselves developers with their own projects, the review
  177. process can be quite lengthy, and some amount of patience is required. If you find
  178. that you've been waiting for a pull request to be given attention for several
  179. months, there may be a number of reasons for this, some of which you can do something
  180. about:
  181. - It may be because of a feature freeze due to an upcoming release. During this time,
  182. only bug fixes are taken into consideration. If your pull request is a new feature,
  183. it will not be prioritized until the release is over. Wait for release.
  184. - It may be because the changes you are suggesting do not appeal to people. Rather than
  185. nits and critique, which require effort and means they care enough to spend time on your
  186. contribution, thundering silence is a good sign of widespread (mild) dislike of a given change
  187. (because people don't assume *others* won't actually like the proposal). Don't take
  188. that personally, though! Instead, take another critical look at what you are suggesting
  189. and see if it: changes too much, is too broad, doesn't adhere to the
  190. [developer notes](doc/, is dangerous or insecure, is messily written, etc.
  191. Identify and address any of the issues you find. Then ask e.g. on IRC if someone could give
  192. their opinion on the concept itself.
  193. - It may be because your code is too complex for all but a few people. And those people
  194. may not have realized your pull request even exists. A great way to find people who
  195. are qualified and care about the code you are touching is the
  196. [Git Blame feature]( Simply
  197. find the person touching the code you are touching before you and see if you can find
  198. them and give them a nudge. Don't be incessant about the nudging though.
  199. - Finally, if all else fails, ask on IRC or elsewhere for someone to give your pull request
  200. a look. If you think you've been waiting an unreasonably long amount of time (month+) for
  201. no particular reason (few lines changed, etc), this is totally fine. Try to return the favor
  202. when someone else is asking for feedback on their code, and universe balances out.
  203. Release Policy
  204. --------------
  205. The project leader is the release manager for each Bitcoin Core release.
  206. Copyright
  207. ---------
  208. By contributing to this repository, you agree to license your work under the
  209. MIT license unless specified otherwise in `contrib/debian/copyright` or at
  210. the top of the file itself. Any work contributed where you are not the original
  211. author must contain its license header with the original author(s) and source.