1===================== 2LLVM Developer Policy 3===================== 4 5.. contents:: 6 :local: 7 8Introduction 9============ 10 11This document contains the LLVM Developer Policy which defines the project's 12policy towards developers and their contributions. The intent of this policy is 13to eliminate miscommunication, rework, and confusion that might arise from the 14distributed nature of LLVM's development. By stating the policy in clear terms, 15we hope each developer can know ahead of time what to expect when making LLVM 16contributions. This policy covers all llvm.org subprojects, including Clang, 17LLDB, libc++, etc. 18 19This policy is also designed to accomplish the following objectives: 20 21#. Attract both users and developers to the LLVM project. 22 23#. Make life as simple and easy for contributors as possible. 24 25#. Keep the top of Subversion trees as stable as possible. 26 27#. Establish awareness of the project's :ref:`copyright, license, and patent 28 policies <copyright-license-patents>` with contributors to the project. 29 30This policy is aimed at frequent contributors to LLVM. People interested in 31contributing one-off patches can do so in an informal way by sending them to the 32`llvm-commits mailing list 33<http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits>`_ and engaging another 34developer to see it through the process. 35 36Developer Policies 37================== 38 39This section contains policies that pertain to frequent LLVM developers. We 40always welcome `one-off patches`_ from people who do not routinely contribute to 41LLVM, but we expect more from frequent contributors to keep the system as 42efficient as possible for everyone. Frequent LLVM contributors are expected to 43meet the following requirements in order for LLVM to maintain a high standard of 44quality. 45 46Stay Informed 47------------- 48 49Developers should stay informed by reading at least the "dev" mailing list for 50the projects you are interested in, such as `llvmdev 51<http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>`_ for LLVM, `cfe-dev 52<http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev>`_ for Clang, or `lldb-dev 53<http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev>`_ for LLDB. If you are 54doing anything more than just casual work on LLVM, it is suggested that you also 55subscribe to the "commits" mailing list for the subproject you're interested in, 56such as `llvm-commits 57<http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits>`_, `cfe-commits 58<http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits>`_, or `lldb-commits 59<http://lists.cs.uiuc.edu/mailman/listinfo/lldb-commits>`_. Reading the 60"commits" list and paying attention to changes being made by others is a good 61way to see what other people are interested in and watching the flow of the 62project as a whole. 63 64We recommend that active developers register an email account with `LLVM 65Bugzilla <http://llvm.org/bugs/>`_ and preferably subscribe to the `llvm-bugs 66<http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs>`_ email list to keep track 67of bugs and enhancements occurring in LLVM. We really appreciate people who are 68proactive at catching incoming bugs in their components and dealing with them 69promptly. 70 71Please be aware that all public LLVM mailing lists are public and archived, and 72that notices of confidentiality or non-disclosure cannot be respected. 73 74.. _patch: 75.. _one-off patches: 76 77Making a Patch 78-------------- 79 80When making a patch for review, the goal is to make it as easy for the reviewer 81to read it as possible. As such, we recommend that you: 82 83#. Make your patch against the Subversion trunk, not a branch, and not an old 84 version of LLVM. This makes it easy to apply the patch. For information on 85 how to check out SVN trunk, please see the `Getting Started 86 Guide <GettingStarted.html#checkout>`_. 87 88#. Similarly, patches should be submitted soon after they are generated. Old 89 patches may not apply correctly if the underlying code changes between the 90 time the patch was created and the time it is applied. 91 92#. Patches should be made with ``svn diff``, or similar. If you use a 93 different tool, make sure it uses the ``diff -u`` format and that it 94 doesn't contain clutter which makes it hard to read. 95 96#. If you are modifying generated files, such as the top-level ``configure`` 97 script, please separate out those changes into a separate patch from the rest 98 of your changes. 99 100When sending a patch to a mailing list, it is a good idea to send it as an 101*attachment* to the message, not embedded into the text of the message. This 102ensures that your mailer will not mangle the patch when it sends it (e.g. by 103making whitespace changes or by wrapping lines). 104 105*For Thunderbird users:* Before submitting a patch, please open *Preferences > 106Advanced > General > Config Editor*, find the key 107``mail.content_disposition_type``, and set its value to ``1``. Without this 108setting, Thunderbird sends your attachment using ``Content-Disposition: inline`` 109rather than ``Content-Disposition: attachment``. Apple Mail gamely displays such 110a file inline, making it difficult to work with for reviewers using that 111program. 112 113When submitting patches, please do not add confidentiality or non-disclosure 114notices to the patches themselves. These notices conflict with the `LLVM 115License`_ and may result in your contribution being excluded. 116 117.. _code review: 118 119Code Reviews 120------------ 121 122LLVM has a code review policy. Code review is one way to increase the quality of 123software. We generally follow these policies: 124 125#. All developers are required to have significant changes reviewed before they 126 are committed to the repository. 127 128#. Code reviews are conducted by email, usually on the llvm-commits list. 129 130#. Code can be reviewed either before it is committed or after. We expect major 131 changes to be reviewed before being committed, but smaller changes (or 132 changes where the developer owns the component) can be reviewed after commit. 133 134#. The developer responsible for a code change is also responsible for making 135 all necessary review-related changes. 136 137#. Code review can be an iterative process, which continues until the patch is 138 ready to be committed. Specifically, once a patch is sent out for review, it 139 needs an explicit "looks good" before it is submitted. Do not assume silent 140 approval, or request active objections to the patch with a deadline. 141 142Sometimes code reviews will take longer than you would hope for, especially for 143larger features. Accepted ways to speed up review times for your patches are: 144 145* Review other people's patches. If you help out, everybody will be more 146 willing to do the same for you; goodwill is our currency. 147* Ping the patch. If it is urgent, provide reasons why it is important to you to 148 get this patch landed and ping it every couple of days. If it is 149 not urgent, the common courtesy ping rate is one week. Remember that you're 150 asking for valuable time from other professional developers. 151* Ask for help on IRC. Developers on IRC will be able to either help you 152 directly, or tell you who might be a good reviewer. 153* Split your patch into multiple smaller patches that build on each other. The 154 smaller your patch, the higher the probability that somebody will take a quick 155 look at it. 156 157Developers should participate in code reviews as both reviewers and 158reviewees. If someone is kind enough to review your code, you should return the 159favor for someone else. Note that anyone is welcome to review and give feedback 160on a patch, but only people with Subversion write access can approve it. 161 162There is a web based code review tool that can optionally be used 163for code reviews. See :doc:`Phabricator`. 164 165Code Owners 166----------- 167 168The LLVM Project relies on two features of its process to maintain rapid 169development in addition to the high quality of its source base: the combination 170of code review plus post-commit review for trusted maintainers. Having both is 171a great way for the project to take advantage of the fact that most people do 172the right thing most of the time, and only commit patches without pre-commit 173review when they are confident they are right. 174 175The trick to this is that the project has to guarantee that all patches that are 176committed are reviewed after they go in: you don't want everyone to assume 177someone else will review it, allowing the patch to go unreviewed. To solve this 178problem, we have a notion of an 'owner' for a piece of the code. The sole 179responsibility of a code owner is to ensure that a commit to their area of the 180code is appropriately reviewed, either by themself or by someone else. The list 181of current code owners can be found in the file 182`CODE_OWNERS.TXT <http://llvm.org/viewvc/llvm-project/llvm/trunk/CODE_OWNERS.TXT?view=markup>`_ 183in the root of the LLVM source tree. 184 185Note that code ownership is completely different than reviewers: anyone can 186review a piece of code, and we welcome code review from anyone who is 187interested. Code owners are the "last line of defense" to guarantee that all 188patches that are committed are actually reviewed. 189 190Being a code owner is a somewhat unglamorous position, but it is incredibly 191important for the ongoing success of the project. Because people get busy, 192interests change, and unexpected things happen, code ownership is purely opt-in, 193and anyone can choose to resign their "title" at any time. For now, we do not 194have an official policy on how one gets elected to be a code owner. 195 196.. _include a testcase: 197 198Test Cases 199---------- 200 201Developers are required to create test cases for any bugs fixed and any new 202features added. Some tips for getting your testcase approved: 203 204* All feature and regression test cases are added to the ``llvm/test`` 205 directory. The appropriate sub-directory should be selected (see the 206 :doc:`Testing Guide <TestingGuide>` for details). 207 208* Test cases should be written in `LLVM assembly language <LangRef.html>`_ 209 unless the feature or regression being tested requires another language 210 (e.g. the bug being fixed or feature being implemented is in the llvm-gcc C++ 211 front-end, in which case it must be written in C++). 212 213* Test cases, especially for regressions, should be reduced as much as possible, 214 by `bugpoint <Bugpoint.html>`_ or manually. It is unacceptable to place an 215 entire failing program into ``llvm/test`` as this creates a *time-to-test* 216 burden on all developers. Please keep them short. 217 218Note that llvm/test and clang/test are designed for regression and small feature 219tests only. More extensive test cases (e.g., entire applications, benchmarks, 220etc) should be added to the ``llvm-test`` test suite. The llvm-test suite is 221for coverage (correctness, performance, etc) testing, not feature or regression 222testing. 223 224Quality 225------- 226 227The minimum quality standards that any change must satisfy before being 228committed to the main development branch are: 229 230#. Code must adhere to the `LLVM Coding Standards <CodingStandards.html>`_. 231 232#. Code must compile cleanly (no errors, no warnings) on at least one platform. 233 234#. Bug fixes and new features should `include a testcase`_ so we know if the 235 fix/feature ever regresses in the future. 236 237#. Code must pass the ``llvm/test`` test suite. 238 239#. The code must not cause regressions on a reasonable subset of llvm-test, 240 where "reasonable" depends on the contributor's judgement and the scope of 241 the change (more invasive changes require more testing). A reasonable subset 242 might be something like "``llvm-test/MultiSource/Benchmarks``". 243 244Additionally, the committer is responsible for addressing any problems found in 245the future that the change is responsible for. For example: 246 247* The code should compile cleanly on all supported platforms. 248 249* The changes should not cause any correctness regressions in the ``llvm-test`` 250 suite and must not cause any major performance regressions. 251 252* The change set should not cause performance or correctness regressions for the 253 LLVM tools. 254 255* The changes should not cause performance or correctness regressions in code 256 compiled by LLVM on all applicable targets. 257 258* You are expected to address any `Bugzilla bugs <http://llvm.org/bugs/>`_ that 259 result from your change. 260 261We prefer for this to be handled before submission but understand that it isn't 262possible to test all of this for every submission. Our build bots and nightly 263testing infrastructure normally finds these problems. A good rule of thumb is 264to check the nightly testers for regressions the day after your change. Build 265bots will directly email you if a group of commits that included yours caused a 266failure. You are expected to check the build bot messages to see if they are 267your fault and, if so, fix the breakage. 268 269Commits that violate these quality standards (e.g. are very broken) may be 270reverted. This is necessary when the change blocks other developers from making 271progress. The developer is welcome to re-commit the change after the problem has 272been fixed. 273 274Obtaining Commit Access 275----------------------- 276 277We grant commit access to contributors with a track record of submitting high 278quality patches. If you would like commit access, please send an email to 279`Chris <mailto:sabre@nondot.org>`_ with the following information: 280 281#. The user name you want to commit with, e.g. "hacker". 282 283#. The full name and email address you want message to llvm-commits to come 284 from, e.g. "J. Random Hacker <hacker@yoyodyne.com>". 285 286#. A "password hash" of the password you want to use, e.g. "``2ACR96qjUqsyM``". 287 Note that you don't ever tell us what your password is; you just give it to 288 us in an encrypted form. To get this, run "``htpasswd``" (a utility that 289 comes with apache) in crypt mode (often enabled with "``-d``"), or find a web 290 page that will do it for you. 291 292Once you've been granted commit access, you should be able to check out an LLVM 293tree with an SVN URL of "https://username@llvm.org/..." instead of the normal 294anonymous URL of "http://llvm.org/...". The first time you commit you'll have 295to type in your password. Note that you may get a warning from SVN about an 296untrusted key; you can ignore this. To verify that your commit access works, 297please do a test commit (e.g. change a comment or add a blank line). Your first 298commit to a repository may require the autogenerated email to be approved by a 299mailing list. This is normal and will be done when the mailing list owner has 300time. 301 302If you have recently been granted commit access, these policies apply: 303 304#. You are granted *commit-after-approval* to all parts of LLVM. To get 305 approval, submit a `patch`_ to `llvm-commits 306 <http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits>`_. When approved, 307 you may commit it yourself. 308 309#. You are allowed to commit patches without approval which you think are 310 obvious. This is clearly a subjective decision --- we simply expect you to 311 use good judgement. Examples include: fixing build breakage, reverting 312 obviously broken patches, documentation/comment changes, any other minor 313 changes. 314 315#. You are allowed to commit patches without approval to those portions of LLVM 316 that you have contributed or maintain (i.e., have been assigned 317 responsibility for), with the proviso that such commits must not break the 318 build. This is a "trust but verify" policy, and commits of this nature are 319 reviewed after they are committed. 320 321#. Multiple violations of these policies or a single egregious violation may 322 cause commit access to be revoked. 323 324In any case, your changes are still subject to `code review`_ (either before or 325after they are committed, depending on the nature of the change). You are 326encouraged to review other peoples' patches as well, but you aren't required 327to do so. 328 329.. _discuss the change/gather consensus: 330 331Making a Major Change 332--------------------- 333 334When a developer begins a major new project with the aim of contributing it back 335to LLVM, s/he should inform the community with an email to the `llvmdev 336<http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>`_ email list, to the extent 337possible. The reason for this is to: 338 339#. keep the community informed about future changes to LLVM, 340 341#. avoid duplication of effort by preventing multiple parties working on the 342 same thing and not knowing about it, and 343 344#. ensure that any technical issues around the proposed work are discussed and 345 resolved before any significant work is done. 346 347The design of LLVM is carefully controlled to ensure that all the pieces fit 348together well and are as consistent as possible. If you plan to make a major 349change to the way LLVM works or want to add a major new extension, it is a good 350idea to get consensus with the development community before you start working on 351it. 352 353Once the design of the new feature is finalized, the work itself should be done 354as a series of `incremental changes`_, not as a long-term development branch. 355 356.. _incremental changes: 357 358Incremental Development 359----------------------- 360 361In the LLVM project, we do all significant changes as a series of incremental 362patches. We have a strong dislike for huge changes or long-term development 363branches. Long-term development branches have a number of drawbacks: 364 365#. Branches must have mainline merged into them periodically. If the branch 366 development and mainline development occur in the same pieces of code, 367 resolving merge conflicts can take a lot of time. 368 369#. Other people in the community tend to ignore work on branches. 370 371#. Huge changes (produced when a branch is merged back onto mainline) are 372 extremely difficult to `code review`_. 373 374#. Branches are not routinely tested by our nightly tester infrastructure. 375 376#. Changes developed as monolithic large changes often don't work until the 377 entire set of changes is done. Breaking it down into a set of smaller 378 changes increases the odds that any of the work will be committed to the main 379 repository. 380 381To address these problems, LLVM uses an incremental development style and we 382require contributors to follow this practice when making a large/invasive 383change. Some tips: 384 385* Large/invasive changes usually have a number of secondary changes that are 386 required before the big change can be made (e.g. API cleanup, etc). These 387 sorts of changes can often be done before the major change is done, 388 independently of that work. 389 390* The remaining inter-related work should be decomposed into unrelated sets of 391 changes if possible. Once this is done, define the first increment and get 392 consensus on what the end goal of the change is. 393 394* Each change in the set can be stand alone (e.g. to fix a bug), or part of a 395 planned series of changes that works towards the development goal. 396 397* Each change should be kept as small as possible. This simplifies your work 398 (into a logical progression), simplifies code review and reduces the chance 399 that you will get negative feedback on the change. Small increments also 400 facilitate the maintenance of a high quality code base. 401 402* Often, an independent precursor to a big change is to add a new API and slowly 403 migrate clients to use the new API. Each change to use the new API is often 404 "obvious" and can be committed without review. Once the new API is in place 405 and used, it is much easier to replace the underlying implementation of the 406 API. This implementation change is logically separate from the API 407 change. 408 409If you are interested in making a large change, and this scares you, please make 410sure to first `discuss the change/gather consensus`_ then ask about the best way 411to go about making the change. 412 413Attribution of Changes 414---------------------- 415 416We believe in correct attribution of contributions to their contributors. 417However, we do not want the source code to be littered with random attributions 418"this code written by J. Random Hacker" (this is noisy and distracting). In 419practice, the revision control system keeps a perfect history of who changed 420what, and the CREDITS.txt file describes higher-level contributions. If you 421commit a patch for someone else, please say "patch contributed by J. Random 422Hacker!" in the commit message. 423 424Overall, please do not add contributor names to the source code. 425 426.. _copyright-license-patents: 427 428Copyright, License, and Patents 429=============================== 430 431.. note:: 432 433 This section deals with legal matters but does not provide legal advice. We 434 are not lawyers --- please seek legal counsel from an attorney. 435 436This section addresses the issues of copyright, license and patents for the LLVM 437project. The copyright for the code is held by the individual contributors of 438the code and the terms of its license to LLVM users and developers is the 439`University of Illinois/NCSA Open Source License 440<http://www.opensource.org/licenses/UoI-NCSA.php>`_ (with portions dual licensed 441under the `MIT License <http://www.opensource.org/licenses/mit-license.php>`_, 442see below). As contributor to the LLVM project, you agree to allow any 443contributions to the project to licensed under these terms. 444 445Copyright 446--------- 447 448The LLVM project does not require copyright assignments, which means that the 449copyright for the code in the project is held by its respective contributors who 450have each agreed to release their contributed code under the terms of the `LLVM 451License`_. 452 453An implication of this is that the LLVM license is unlikely to ever change: 454changing it would require tracking down all the contributors to LLVM and getting 455them to agree that a license change is acceptable for their contribution. Since 456there are no plans to change the license, this is not a cause for concern. 457 458As a contributor to the project, this means that you (or your company) retain 459ownership of the code you contribute, that it cannot be used in a way that 460contradicts the license (which is a liberal BSD-style license), and that the 461license for your contributions won't change without your approval in the 462future. 463 464.. _LLVM License: 465 466License 467------- 468 469We intend to keep LLVM perpetually open source and to use a liberal open source 470license. **As a contributor to the project, you agree that any contributions be 471licensed under the terms of the corresponding subproject.** All of the code in 472LLVM is available under the `University of Illinois/NCSA Open Source License 473<http://www.opensource.org/licenses/UoI-NCSA.php>`_, which boils down to 474this: 475 476* You can freely distribute LLVM. 477* You must retain the copyright notice if you redistribute LLVM. 478* Binaries derived from LLVM must reproduce the copyright notice (e.g. in an 479 included readme file). 480* You can't use our names to promote your LLVM derived products. 481* There's no warranty on LLVM at all. 482 483We believe this fosters the widest adoption of LLVM because it **allows 484commercial products to be derived from LLVM** with few restrictions and without 485a requirement for making any derived works also open source (i.e. LLVM's 486license is not a "copyleft" license like the GPL). We suggest that you read the 487`License <http://www.opensource.org/licenses/UoI-NCSA.php>`_ if further 488clarification is needed. 489 490In addition to the UIUC license, the runtime library components of LLVM 491(**compiler_rt, libc++, and libclc**) are also licensed under the `MIT License 492<http://www.opensource.org/licenses/mit-license.php>`_, which does not contain 493the binary redistribution clause. As a user of these runtime libraries, it 494means that you can choose to use the code under either license (and thus don't 495need the binary redistribution clause), and as a contributor to the code that 496you agree that any contributions to these libraries be licensed under both 497licenses. We feel that this is important for runtime libraries, because they 498are implicitly linked into applications and therefore should not subject those 499applications to the binary redistribution clause. This also means that it is ok 500to move code from (e.g.) libc++ to the LLVM core without concern, but that code 501cannot be moved from the LLVM core to libc++ without the copyright owner's 502permission. 503 504Note that the LLVM Project does distribute llvm-gcc and dragonegg, **which are 505GPL.** This means that anything "linked" into llvm-gcc must itself be compatible 506with the GPL, and must be releasable under the terms of the GPL. This implies 507that **any code linked into llvm-gcc and distributed to others may be subject to 508the viral aspects of the GPL** (for example, a proprietary code generator linked 509into llvm-gcc must be made available under the GPL). This is not a problem for 510code already distributed under a more liberal license (like the UIUC license), 511and GPL-containing subprojects are kept in separate SVN repositories whose 512LICENSE.txt files specifically indicate that they contain GPL code. 513 514We have no plans to change the license of LLVM. If you have questions or 515comments about the license, please contact the `LLVM Developer's Mailing 516List <mailto:llvmdev@cs.uiuc.edu>`_. 517 518Patents 519------- 520 521To the best of our knowledge, LLVM does not infringe on any patents (we have 522actually removed code from LLVM in the past that was found to infringe). Having 523code in LLVM that infringes on patents would violate an important goal of the 524project by making it hard or impossible to reuse the code for arbitrary purposes 525(including commercial use). 526 527When contributing code, we expect contributors to notify us of any potential for 528patent-related trouble with their changes (including from third parties). If 529you or your employer own the rights to a patent and would like to contribute 530code to LLVM that relies on it, we require that the copyright owner sign an 531agreement that allows any other user of LLVM to freely use your patent. Please 532contact the `oversight group <mailto:llvm-oversight@cs.uiuc.edu>`_ for more 533details. 534