/ CONTRIBUTING.md
CONTRIBUTING.md
1 Contributing to Bitcoin Core 2 ============================ 3 4 The Bitcoin Core project operates an open contributor model where anyone is 5 welcome to contribute towards development in the form of peer review, testing 6 and patches. This document explains the practical process and guidelines for 7 contributing. 8 9 First, in terms of structure, there is no particular concept of "Bitcoin Core 10 developers" in the sense of privileged people. Open source often naturally 11 revolves around a meritocracy where contributors earn trust from the developer 12 community over time. Nevertheless, some hierarchy is necessary for practical 13 purposes. As such, there are repository maintainers who are responsible for 14 merging pull requests, the [release cycle](/doc/release-process.md), and 15 moderation. 16 17 Getting Started 18 --------------- 19 20 New contributors are very welcome and needed. 21 22 Reviewing and testing is highly valued and the most effective way you can contribute 23 as a new contributor. It also will teach you much more about the code and 24 process than opening pull requests. Please refer to the [peer review](#peer-review) 25 section below. 26 27 Before you start contributing, familiarize yourself with the Bitcoin Core build 28 system and tests. Refer to the documentation in the repository on how to build 29 Bitcoin Core and how to run the unit tests, functional tests, and fuzz tests. 30 31 There are many open issues of varying difficulty waiting to be fixed. 32 If you're looking for somewhere to start contributing, check out the 33 [good first issue](https://github.com/bitcoin/bitcoin/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22) 34 list or changes that are 35 [up for grabs](https://github.com/bitcoin/bitcoin/issues?utf8=%E2%9C%93&q=label%3A%22Up+for+grabs%22). 36 Some of them might no longer be applicable. So if you are interested, but 37 unsure, you might want to leave a comment on the issue first. 38 39 You may also participate in the weekly 40 [Bitcoin Core PR Review Club](https://bitcoincore.reviews/) meeting. 41 42 ### Good First Issue Label 43 44 The purpose of the `good first issue` label is to highlight which issues are 45 suitable for a new contributor without a deep understanding of the codebase. 46 47 However, good first issues can be solved by anyone. If they remain unsolved 48 for a longer time, a frequent contributor might address them. 49 50 You do not need to request permission to start working on an issue. However, 51 you are encouraged to leave a comment if you are planning to work on it. This 52 will help other contributors monitor which issues are actively being addressed 53 and is also an effective way to request assistance if and when you need it. 54 55 Communication Channels 56 ---------------------- 57 58 Most communication about Bitcoin Core development happens on IRC, in the 59 `#bitcoin-core-dev` channel on Libera Chat. The easiest way to participate on IRC is 60 with the web client, [web.libera.chat](https://web.libera.chat/#bitcoin-core-dev). Chat 61 history logs can be found 62 on [https://www.erisian.com.au/bitcoin-core-dev/](https://www.erisian.com.au/bitcoin-core-dev/) 63 and [https://gnusha.org/bitcoin-core-dev/](https://gnusha.org/bitcoin-core-dev/). 64 65 Discussion about codebase improvements happens in GitHub issues and pull 66 requests. 67 68 The developer 69 [mailing list](https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev) 70 should be used to discuss complicated or controversial consensus or P2P protocol changes before working on 71 a patch set. 72 73 74 Contributor Workflow 75 -------------------- 76 77 The codebase is maintained using the "contributor workflow" where everyone 78 without exception contributes patch proposals using "pull requests" (PRs). This 79 facilitates social contribution, easy testing and peer review. 80 81 To contribute a patch, the workflow is as follows: 82 83 1. Fork repository ([only for the first time](https://docs.github.com/en/get-started/quickstart/fork-a-repo)) 84 1. Create topic branch 85 1. Commit patches 86 87 For GUI-related issues or pull requests, the https://github.com/bitcoin-core/gui repository should be used. 88 For all other issues and pull requests, the https://github.com/bitcoin/bitcoin node repository should be used. 89 90 The master branch for all monotree repositories is identical. 91 92 As a rule of thumb, everything that only modifies `src/qt` is a GUI-only pull 93 request. However: 94 95 * For global refactoring or other transversal changes the node repository 96 should be used. 97 * For GUI-related build system changes, the node repository should be used 98 because the change needs review by the build systems reviewers. 99 * Changes in `src/interfaces` need to go to the node repository because they 100 might affect other components like the wallet. 101 102 For large GUI changes that include build system and interface changes, it is 103 recommended to first open a pull request against the GUI repository. When there 104 is agreement to proceed with the changes, a pull request with the build system 105 and interfaces changes can be submitted to the node repository. 106 107 The project coding conventions in the [developer notes](doc/developer-notes.md) 108 must be followed. 109 110 ### Committing Patches 111 112 In general, [commits should be atomic](https://en.wikipedia.org/wiki/Atomic_commit#Atomic_commit_convention) 113 and diffs should be easy to read. For this reason, do not mix any formatting 114 fixes or code moves with actual code changes. 115 116 Make sure each individual commit is hygienic: that it builds successfully on its 117 own without warnings, errors, regressions, or test failures. 118 119 Commit messages should be verbose by default consisting of a short subject line 120 (50 chars max), a blank line and detailed explanatory text as separate 121 paragraph(s), unless the title alone is self-explanatory (like "Correct typo 122 in init.cpp") in which case a single title line is sufficient. Commit messages should be 123 helpful to people reading your code in the future, so explain the reasoning for 124 your decisions. Further explanation [here](https://chris.beams.io/posts/git-commit/). 125 126 If a particular commit references another issue, please add the reference. For 127 example: `refs #1234` or `fixes #4321`. Using the `fixes` or `closes` keywords 128 will cause the corresponding issue to be closed when the pull request is merged. 129 130 Commit messages should never contain any `@` mentions (usernames prefixed with "@"). 131 132 Please refer to the [Git manual](https://git-scm.com/doc) for more information 133 about Git. 134 135 - Push changes to your fork 136 - Create pull request 137 138 ### Creating the Pull Request 139 140 The title of the pull request should be prefixed by the component or area that 141 the pull request affects. Valid areas as: 142 143 - `consensus` for changes to consensus critical code 144 - `doc` for changes to the documentation 145 - `qt` or `gui` for changes to bitcoin-qt 146 - `log` for changes to log messages 147 - `mining` for changes to the mining code 148 - `net` or `p2p` for changes to the peer-to-peer network code 149 - `refactor` for structural changes that do not change behavior 150 - `rpc`, `rest` or `zmq` for changes to the RPC, REST or ZMQ APIs 151 - `script` for changes to the scripts and tools 152 - `test`, `qa` or `ci` for changes to the unit tests, QA tests or CI code 153 - `util` or `lib` for changes to the utils or libraries 154 - `wallet` for changes to the wallet code 155 - `build` for changes to the GNU Autotools or MSVC builds 156 - `guix` for changes to the GUIX reproducible builds 157 158 Examples: 159 160 consensus: Add new opcode for BIP-XXXX OP_CHECKAWESOMESIG 161 net: Automatically create onion service, listen on Tor 162 qt: Add feed bump button 163 log: Fix typo in log message 164 165 The body of the pull request should contain sufficient description of *what* the 166 patch does, and even more importantly, *why*, with justification and reasoning. 167 You should include references to any discussions (for example, other issues or 168 mailing list discussions). 169 170 The description for a new pull request should not contain any `@` mentions. The 171 PR description will be included in the commit message when the PR is merged and 172 any users mentioned in the description will be annoyingly notified each time a 173 fork of Bitcoin Core copies the merge. Instead, make any username mentions in a 174 subsequent comment to the PR. 175 176 ### Translation changes 177 178 Note that translations should not be submitted as pull requests. Please see 179 [Translation Process](https://github.com/bitcoin/bitcoin/blob/master/doc/translation_process.md) 180 for more information on helping with translations. 181 182 ### Work in Progress Changes and Requests for Comments 183 184 If a pull request is not to be considered for merging (yet), please 185 prefix the title with [WIP] or use [Tasks Lists](https://docs.github.com/en/github/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#task-lists) 186 in the body of the pull request to indicate tasks are pending. 187 188 ### Address Feedback 189 190 At this stage, one should expect comments and review from other contributors. You 191 can add more commits to your pull request by committing them locally and pushing 192 to your fork. 193 194 You are expected to reply to any review comments before your pull request is 195 merged. You may update the code or reject the feedback if you do not agree with 196 it, but you should express so in a reply. If there is outstanding feedback and 197 you are not actively working on it, your pull request may be closed. 198 199 Please refer to the [peer review](#peer-review) section below for more details. 200 201 ### Squashing Commits 202 203 If your pull request contains fixup commits (commits that change the same line of code repeatedly) or too fine-grained 204 commits, you may be asked to [squash](https://git-scm.com/docs/git-rebase#_interactive_mode) your commits 205 before it will be reviewed. The basic squashing workflow is shown below. 206 207 git checkout your_branch_name 208 git rebase -i HEAD~n 209 # n is normally the number of commits in the pull request. 210 # Set commits (except the one in the first line) from 'pick' to 'squash', save and quit. 211 # On the next screen, edit/refine commit messages. 212 # Save and quit. 213 git push -f # (force push to GitHub) 214 215 Please update the resulting commit message, if needed. It should read as a 216 coherent message. In most cases, this means not just listing the interim 217 commits. 218 219 If your change contains a merge commit, the above workflow may not work and you 220 will need to remove the merge commit first. See the next section for details on 221 how to rebase. 222 223 Please refrain from creating several pull requests for the same change. 224 Use the pull request that is already open (or was created earlier) to amend 225 changes. This preserves the discussion and review that happened earlier for 226 the respective change set. 227 228 The length of time required for peer review is unpredictable and will vary from 229 pull request to pull request. 230 231 ### Rebasing Changes 232 233 When a pull request conflicts with the target branch, you may be asked to rebase it on top of the current target branch. 234 235 git fetch https://github.com/bitcoin/bitcoin # Fetch the latest upstream commit 236 git rebase FETCH_HEAD # Rebuild commits on top of the new base 237 238 This project aims to have a clean git history, where code changes are only made in non-merge commits. This simplifies 239 auditability because merge commits can be assumed to not contain arbitrary code changes. Merge commits should be signed, 240 and the resulting git tree hash must be deterministic and reproducible. The script in 241 [/contrib/verify-commits](/contrib/verify-commits) checks that. 242 243 After a rebase, reviewers are encouraged to sign off on the force push. This should be relatively straightforward with 244 the `git range-diff` tool explained in the [productivity 245 notes](/doc/productivity.md#diff-the-diffs-with-git-range-diff). To avoid needless review churn, maintainers will 246 generally merge pull requests that received the most review attention first. 247 248 Pull Request Philosophy 249 ----------------------- 250 251 Patchsets should always be focused. For example, a pull request could add a 252 feature, fix a bug, or refactor code; but not a mixture. Please also avoid super 253 pull requests which attempt to do too much, are overly large, or overly complex 254 as this makes review difficult. 255 256 257 ### Features 258 259 When adding a new feature, thought must be given to the long term technical debt 260 and maintenance that feature may require after inclusion. Before proposing a new 261 feature that will require maintenance, please consider if you are willing to 262 maintain it (including bug fixing). If features get orphaned with no maintainer 263 in the future, they may be removed by the Repository Maintainer. 264 265 266 ### Refactoring 267 268 Refactoring is a necessary part of any software project's evolution. The 269 following guidelines cover refactoring pull requests for the project. 270 271 There are three categories of refactoring: code-only moves, code style fixes, and 272 code refactoring. In general, refactoring pull requests should not mix these 273 three kinds of activities in order to make refactoring pull requests easy to 274 review and uncontroversial. In all cases, refactoring PRs must not change the 275 behaviour of code within the pull request (bugs must be preserved as is). 276 277 Project maintainers aim for a quick turnaround on refactoring pull requests, so 278 where possible keep them short, uncomplex and easy to verify. 279 280 Pull requests that refactor the code should not be made by new contributors. It 281 requires a certain level of experience to know where the code belongs to and to 282 understand the full ramification (including rebase effort of open pull requests). 283 284 Trivial pull requests or pull requests that refactor the code with no clear 285 benefits may be immediately closed by the maintainers to reduce unnecessary 286 workload on reviewing. 287 288 289 "Decision Making" Process 290 ------------------------- 291 292 The following applies to code changes to the Bitcoin Core project (and related 293 projects such as libsecp256k1), and is not to be confused with overall Bitcoin 294 Network Protocol consensus changes. 295 296 Whether a pull request is merged into Bitcoin Core rests with the project merge 297 maintainers. 298 299 Maintainers will take into consideration if a patch is in line with the general 300 principles of the project; meets the minimum standards for inclusion; and will 301 judge the general consensus of contributors. 302 303 In general, all pull requests must: 304 305 - Have a clear use case, fix a demonstrable bug or serve the greater good of 306 the project (for example refactoring for modularisation); 307 - Be well peer-reviewed; 308 - Have unit tests, functional tests, and fuzz tests, where appropriate; 309 - Follow code style guidelines ([C++](doc/developer-notes.md), [functional tests](test/functional/README.md)); 310 - Not break the existing test suite; 311 - Where bugs are fixed, where possible, there should be unit tests 312 demonstrating the bug and also proving the fix. This helps prevent regression. 313 - Change relevant comments and documentation when behaviour of code changes. 314 315 Patches that change Bitcoin consensus rules are considerably more involved than 316 normal because they affect the entire ecosystem and so must be preceded by 317 extensive mailing list discussions and have a numbered BIP. While each case will 318 be different, one should be prepared to expend more time and effort than for 319 other kinds of patches because of increased peer review and consensus building 320 requirements. 321 322 323 ### Peer Review 324 325 Anyone may participate in peer review which is expressed by comments in the pull 326 request. Typically reviewers will review the code for obvious errors, as well as 327 test out the patch set and opine on the technical merits of the patch. Project 328 maintainers take into account the peer review when determining if there is 329 consensus to merge a pull request (remember that discussions may have been 330 spread out over GitHub, mailing list and IRC discussions). 331 332 Code review is a burdensome but important part of the development process, and 333 as such, certain types of pull requests are rejected. In general, if the 334 **improvements** do not warrant the **review effort** required, the PR has a 335 high chance of being rejected. It is up to the PR author to convince the 336 reviewers that the changes warrant the review effort, and if reviewers are 337 "Concept NACK'ing" the PR, the author may need to present arguments and/or do 338 research backing their suggested changes. 339 340 #### Conceptual Review 341 342 A review can be a conceptual review, where the reviewer leaves a comment 343 * `Concept (N)ACK`, meaning "I do (not) agree with the general goal of this pull 344 request", 345 * `Approach (N)ACK`, meaning `Concept ACK`, but "I do (not) agree with the 346 approach of this change". 347 348 A `NACK` needs to include a rationale why the change is not worthwhile. 349 NACKs without accompanying reasoning may be disregarded. 350 351 #### Code Review 352 353 After conceptual agreement on the change, code review can be provided. A review 354 begins with `ACK BRANCH_COMMIT`, where `BRANCH_COMMIT` is the top of the PR 355 branch, followed by a description of how the reviewer did the review. The 356 following language is used within pull request comments: 357 358 - "I have tested the code", involving change-specific manual testing in 359 addition to running the unit, functional, or fuzz tests, and in case it is 360 not obvious how the manual testing was done, it should be described; 361 - "I have not tested the code, but I have reviewed it and it looks 362 OK, I agree it can be merged"; 363 - A "nit" refers to a trivial, often non-blocking issue. 364 365 Project maintainers reserve the right to weigh the opinions of peer reviewers 366 using common sense judgement and may also weigh based on merit. Reviewers that 367 have demonstrated a deeper commitment and understanding of the project over time 368 or who have clear domain expertise may naturally have more weight, as one would 369 expect in all walks of life. 370 371 Where a patch set affects consensus-critical code, the bar will be much 372 higher in terms of discussion and peer review requirements, keeping in mind that 373 mistakes could be very costly to the wider community. This includes refactoring 374 of consensus-critical code. 375 376 Where a patch set proposes to change the Bitcoin consensus, it must have been 377 discussed extensively on the mailing list and IRC, be accompanied by a widely 378 discussed BIP and have a generally widely perceived technical consensus of being 379 a worthwhile change based on the judgement of the maintainers. 380 381 ### Finding Reviewers 382 383 As most reviewers are themselves developers with their own projects, the review 384 process can be quite lengthy, and some amount of patience is required. If you find 385 that you've been waiting for a pull request to be given attention for several 386 months, there may be a number of reasons for this, some of which you can do something 387 about: 388 389 - It may be because of a feature freeze due to an upcoming release. During this time, 390 only bug fixes are taken into consideration. If your pull request is a new feature, 391 it will not be prioritized until after the release. Wait for the release. 392 - It may be because the changes you are suggesting do not appeal to people. Rather than 393 nits and critique, which require effort and means they care enough to spend time on your 394 contribution, thundering silence is a good sign of widespread (mild) dislike of a given change 395 (because people don't assume *others* won't actually like the proposal). Don't take 396 that personally, though! Instead, take another critical look at what you are suggesting 397 and see if it: changes too much, is too broad, doesn't adhere to the 398 [developer notes](doc/developer-notes.md), is dangerous or insecure, is messily written, etc. 399 Identify and address any of the issues you find. Then ask e.g. on IRC if someone could give 400 their opinion on the concept itself. 401 - It may be because your code is too complex for all but a few people, and those people 402 may not have realized your pull request even exists. A great way to find people who 403 are qualified and care about the code you are touching is the 404 [Git Blame feature](https://docs.github.com/en/github/managing-files-in-a-repository/managing-files-on-github/tracking-changes-in-a-file). Simply 405 look up who last modified the code you are changing and see if you can find 406 them and give them a nudge. Don't be incessant about the nudging, though. 407 - Finally, if all else fails, ask on IRC or elsewhere for someone to give your pull request 408 a look. If you think you've been waiting for an unreasonably long time (say, 409 more than a month) for no particular reason (a few lines changed, etc.), 410 this is totally fine. Try to return the favor when someone else is asking 411 for feedback on their code, and the universe balances out. 412 - Remember that the best thing you can do while waiting is give review to others! 413 414 415 Backporting 416 ----------- 417 418 Security and bug fixes can be backported from `master` to release 419 branches. 420 If the backport is non-trivial, it may be appropriate to open an 421 additional PR to backport the change, but only after the original PR 422 has been merged. 423 Otherwise, backports will be done in batches and 424 the maintainers will use the proper `Needs backport (...)` labels 425 when needed (the original author does not need to worry about it). 426 427 A backport should contain the following metadata in the commit body: 428 429 ``` 430 Github-Pull: #<PR number> 431 Rebased-From: <commit hash of the original commit> 432 ``` 433 434 Have a look at [an example backport PR]( 435 https://github.com/bitcoin/bitcoin/pull/16189). 436 437 Also see the [backport.py script]( 438 https://github.com/bitcoin-core/bitcoin-maintainer-tools#backport). 439 440 Copyright 441 --------- 442 443 By contributing to this repository, you agree to license your work under the 444 MIT license unless specified otherwise in `contrib/debian/copyright` or at 445 the top of the file itself. Any work contributed where you are not the original 446 author must contain its license header with the original author(s) and source.