We follow the standard GitHub [fork & pull](https://help.github.com/articles/using-pull-requests/#fork--pull) approach to pull requests. Just fork the official repo, develop in a branch, and submit a PR!
You're always welcome to submit your PR straight away and start the discussion (without reading the rest of this wonderful doc, or the README.md). The goal of these notes is to make your experience contributing to Akka as smooth and pleasant as possible. We're happy to guide you through the process once you've submitted your PR.
In case of questions about the contribution process or for discussion of specific issues please visit the [akka/dev gitter chat](https://gitter.im/akka/dev).
- [good first issue](https://github.com/akka/akka/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22) - which identifies simple entry level tickets, such as improvements of documentation or tests. If you're not sure how to solve a ticket but would like to work on it feel free to ask in the issue about clarification or tips.
- [help wanted](https://github.com/akka/akka/labels/help%20wanted) - which identifies issues that the core team will likely not have time to work on, or the issue is a nice entry level ticket. If you're not sure how to solve a ticket but would like to work on it feel free to ask in the issue about clarification or tips.
- [nice-to-have (low-priority)](https://github.com/akka/akka/labels/nice-to-have%20%28low-prio%29) - are tasks which make sense, however are not very high priority (in face of other very high priority issues). If you see something interesting in this list, a contribution would be really wonderful!
- [0 - new](https://github.com/akka/akka/labels/0%20-%20new) - is assigned when a ticket is unclear on its purpose or if it is valid or not. Sometimes the additional tag `discuss` is used to mark such tickets, if they propose large scale changes and need more discussion before moving into triaged (or being closed as invalid).
- [1 - triaged](https://github.com/akka/akka/labels/1%20-%20triaged) - roughly speaking means "this ticket makes sense". Triaged tickets are safe to pick up for contributing in terms of likeliness of a patch for it being accepted. It is not recommended to start working on a ticket that is not triaged.
- [2 - pick next](https://github.com/akka/akka/labels/2%20-%20pick%20next) - used to mark issues which are next up in the queue to be worked on. Sometimes it's also used to mark which PRs are expected to be reviewed/merged for the next release. The tag is non-binding, and mostly used as an organisational helper.
- [3 - in progress](https://github.com/akka/akka/labels/3%20-%20in%20progress) - means someone is working on this ticket. If you see a ticket that has the tag, however seems inactive, it could have been an omission with removing the tag, feel free to ping the ticket then if it's still being worked on.
- [bug](https://github.com/akka/akka/labels/bug) - bugs take priority in being fixed above features. The core team dedicates a number of days to working on bugs each sprint. Bugs which have reproducers are also great for community contributions as they're well isolated. Sometimes we're not as lucky to have reproducers though, then a bugfix should also include a test reproducing the original error along with the fix.
- [failed](https://github.com/akka/akka/labels/failed) - tickets indicate a Jenkins failure (for example from a nightly build). These tickets usually include a stacktrace + link to the Jenkins failure, and we'll add a comment when we see the same problem again. Since these tickets can either indicate tests with incorrect assumptions or legitimate issues in the production code we look at them periodically. When the same problem isn't seen again over a period of 6 months we assume it to be a rare flaky test or a problem that might have since been fixed, so we close the issue until it pops up again.
1. To avoid duplicated effort, it might be good to check the [issue tracker](https://github.com/akka/akka/issues) and [existing pull requests](https://github.com/akka/akka/pulls) for existing work.
- If there is no ticket yet, feel free to [create one](https://github.com/akka/akka/issues/new) to discuss the problem and the approach you want to take to solve it.
1. [Fork the project](https://github.com/akka/akka#fork-destination-box) on GitHub. You'll need to create a feature-branch for your work on your fork, as this way you'll be able to submit a pull request against the mainline Akka.
- Please write additional tests covering your feature and adjust existing ones if needed before submitting your pull request. The `validatePullRequest` sbt task ([explained below](#the-validatepullrequest-task)) may come in handy to verify your changes are correct.
1. Once your feature is complete, prepare the commit following our [Creating Commits And Writing Commit Messages](#creating-commits-and-writing-commit-messages). For example, a good commit message would be: `Adding compression support for Manifests #22222` (note the reference to the ticket it aimed to resolve).
1. If it's a new feature, or a change of behavior, document it on the [akka-docs](https://github.com/akka/akka/tree/master/akka-docs). If the feature was touching Scala or Java DSL, make sure to document both the Scala and Java APIs.
- Please make sure to include a reference to the issue you're solving *in the comment* for the Pull Request, as this will cause the PR to be linked properly with the Issue. Examples of good phrases for this are: "Resolves #1234" or "Refs #1234".
1. If you have not already done so, you will be asked by our CLA bot to [sign the Lightbend CLA](http://www.lightbend.com/contribute/cla) online. CLA stands for Contributor License Agreement and is a way of protecting intellectual property disputes from harming the project.
1. A core member will comment `OK TO TEST` on your PR to kick off the build. This is just a sanity check to prevent malicious code from being run on the Jenkins cluster.
1. Now both committers and interested people will review your code. This process is to ensure the code we merge is of the best possible quality, and that no silly mistakes slip through. You're expected to follow-up these comments by adding new commits to the same branch. The commit messages of those commits can be more loose, for example: `Removed debugging using printline`, as they all will be squashed into one commit before merging into the main branch.
- The community and team are really nice people, so don't be afraid to ask follow up questions if you didn't understand some comment, or would like clarification on how to continue with a given feature. We're here to help, so feel free to ask and discuss any kind of questions you might have during review!
1. After the review you should fix the issues as needed (pushing a new commit for new review etc.), iterating until the reviewers give their thumbs up–which is signalled usually by a comment saying `LGTM`, which means "Looks Good To Me".
- In general a PR is expected to get 2 LGTMs from the team before it is merged. If the PR is trivial, or under special circumstances (such as most of the team being on vacation, a PR was very thoroughly reviewed/tested and surely is correct) one LGTM may be fine as well.
1. If the code change needs to be applied to other branches as well (for example a bugfix needing to be backported to a previous version), one of the team will either ask you to submit a PR with the same commit to the old branch, or do this for you.
1. Once everything is said and done, your pull request gets merged :tada: Your feature will be available with the next “earliest” release milestone (i.e. if back-ported so that it will be in release x.y.z, find the relevant milestone for that release). And of course you will be given credit for the fix in the release stats during the release's announcement. You've made it!
Akka is using the [sbt](https://github.com/sbt/sbt) build system. So the first thing you have to do is to download and install sbt. You can read more about how to do that in the [sbt setup](https://www.scala-sbt.org/1.x/docs/Getting-Started.html) documentation.
Akka, like most Scala projects, compiles faster with the Graal JIT enabled. The easiest way to use it for compiling Akka is to:
* Use a JDK > 10
* Use the following JVM options for SBT e.g. by adding them to the `SBT_OPTS` environment variable: `-XX:+UnlockExperimentalVMOptions -XX:+EnableJVMCI -XX:+UseJVMCICompiler`
[error] * method foldAsync(java.lang.Object,scala.Function2)akka.stream.scaladsl.FlowOps in trait akka.stream.scaladsl.FlowOps is present only in current version
Changes to the binary protocol of remoting, cluster and the cluster tools require great care so that it is possible
to do rolling upgrades. Note that this may include older nodes communicating with a newer node so compatibility
may have to be both ways.
Since during a rolling upgrade nodes producing the 'new' format and nodes producing the 'old' format coexist, a change can require a two-release process:
the first change is to add a new binary format but still use the old. A second step then starts actually emitting the
new wire format. This ensures users can complete a rolling upgrade first to the intermediate version and then another
rolling upgrade to the next version.
All wire protocol changes that may concern rolling upgrades should be documented in the
1. A pull request must indicate (link to) the issue it is aimed to resolve in the description (or comments) of the PR, in order to establish a link between PR and Issue. This can be achieved by writing "Fixes #1234" or similar in PR description.
1. The Notices file for the project includes the Lightbend copyright notice and no other files contain copyright notices. See http://www.apache.org/legal/src-headers.html for instructions for managing this approach for copyrights.
- Do not use ``@author`` tags since it does not encourage [Collective Code Ownership](http://www.extremeprogramming.org/rules/collective.html).
- Contributors , each project should make sure that the contributors gets the credit they deserve—in a text file or page on the project website and in the release notes etc.
All documentation is preferred to be in Lightbend's standard documentation format [Paradox](https://github.com/lightbend/paradox), which among other things allows all code in the documentation to be externalized into compiled files and imported into the documentation.
Alternatively, use `akka-docs/paradoxBrowse` to open the generated docs in your default web browser.
### Links to API documentation
Akka Paradox supports directives to link to the Scaladoc- and Javadoc-generated API documentation:
*`@apidoc[Flow]` searches for the class name and creates links to Scaladoc and Javadoc (see variants in [sbt-paradox-apidoc](https://github.com/lightbend/sbt-paradox-apidoc#examples))
*`@scaladoc[Flow](akka.stream.scaladsl.Flow)` (see [Paradox docs](https://developer.lightbend.com/docs/paradox/current/directives/linking.html#scaladoc-directive))
*`@javadoc[Flow](akka.stream.javadsl.Flow)` (see [Paradox docs](https://developer.lightbend.com/docs/paradox/current/directives/linking.html#javadoc-directive))
The Scaladoc tool needs the `dot` command from the Graphviz software package to be installed to avoid errors. You can disable the diagram generation by adding the flag `-Dakka.scaladoc.diagrams=false`. After installing Graphviz, make sure you add the toolset to the PATH (definitely on Windows).
Akka generates JavaDoc-style API documentation using the [genjavadoc](https://github.com/typesafehub/genjavadoc) sbt plugin, since the sources are written mostly in Scala.
Generating JavaDoc is not enabled by default, as it's not needed on day-to-day development as it's expected to just work.
All the external runtime dependencies for the project, including transitive dependencies, must have an open source license that is equal to, or compatible with, [Apache 2](http://www.apache.org/licenses/LICENSE-2.0).
Which licenses are compatible with Apache 2 are defined in [this doc](http://www.apache.org/legal/3party.html#category-a), where you can see that the licenses that are listed under ``Category A`` are automatically compatible with Apache 2, while the ones listed under ``Category B`` need additional action:
> Each license in this category requires some degree of [reciprocity](http://www.apache.org/legal/3party.html#define-reciprocal); therefore, additional action must be taken in order to minimize the chance that a user of an Apache product will create a derivative work of a reciprocally-licensed portion of an Apache product without being aware of the applicable requirements.
Each project must also create and maintain a list of all dependencies and their licenses, including all their transitive dependencies. This can be done either in the documentation or in the build file next to each dependency.
1. If your work spans multiple local commits (for example; if you do safe point commits while working in a feature branch or work in a branch for a long time doing merges/rebases etc.) then please do not commit it all but rewrite the history by squashing the commits into a single big commit which you write a good commit message for (like discussed in the following sections). For more info read this article: [Git Workflow](http://sandofsky.com/blog/git-workflow.html). Every commit should be able to be used in isolation, cherry picked etc.
2. The first line should be a descriptive sentence what the commit is doing, including the ticket number. It should be possible to fully understand what the commit does—but not necessarily how it does it—by just reading this single line. We follow the “imperative present tense” style for commit messages ([more info here](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html)).
This requires a member from a core team to start the pull request validation process by posting a comment consisting only of `OK TO TEST`.
From now on, whenever new commits are pushed to the pull request, a validation job will be automatically started and the results of the validation posted to the pull request.
Note, that `OK TO TEST` will only be picked up when the user asking for it is considered an admin. Public (!) members of the [akka organization](https://github.com/orgs/akka/people) are automatically considered admins and users manually declared admin in the Jenkins job (currently no one is explicitly listed). `PLS BUILD` and `PLS BUILD ALL` can be issued by everyone that is an admin or everyone who was whitelisted in the Jenkins Job (whitelisting != declaring someone an admin).
PR validation includes the discipline flags and therefore may fail if the flags were disabled during development. Make sure you compile your code at least once with discipline enabled before sending a PR.
Avoid short test timeouts, since Jenkins server may GC heavily causing spurious test failures. GC pause or other hiccups of 2 seconds are common in our CI environment. Please note that usually giving a larger timeout *does not slow down the tests*, as in an `expectMessage` call for example it usually will complete quickly.
Special care should be given to `expectNoMessage` calls, which indeed will wait the entire timeout before continuing, therefore a shorter timeout should be used in those, for example `200` or `300.millis`. Prefer the method without timeout parameter, which will use the configured `expect-no-message-default` timeout.
You can read up on `remaining` and friends in [TestKit.scala](https://github.com/akka/akka/blob/master/akka-testkit/src/main/scala/akka/testkit/TestKit.scala).
1. Any method definition in a class that will be part of the Java API should not use any default parameters, as they will show up ugly when using them from Java, use plain old method overloading instead.
