sbt/CONTRIBUTING.md

  [StackOverflow]: http://stackoverflow.com/tags/sbt
  [ask]: https://stackoverflow.com/questions/ask?tags=sbt
  [Setup]: http://www.scala-sbt.org/release/docs/Getting-Started/Setup
  [Issues]: https://github.com/sbt/sbt/issues
  [sbt-dev]: https://groups.google.com/d/forum/sbt-dev
  [sbt-contrib]: https://gitter.im/sbt/sbt-contrib
  [Lightbend]: https://www.lightbend.com/
  [subscriptions]: https://www.lightbend.com/platform/subscription
  [327]: https://github.com/sbt/sbt/issues/327
  [gitter]: https://gitter.im/sbt/sbt
  [documentation]: https://github.com/sbt/website

Support
=======

[Lightbend] sponsors sbt and encourages contributions from the active community. Enterprises can adopt it for mission critical systems with confidence because Lightbend stands behind sbt with commercial support and services.

For community support please [ask] on StackOverflow with the tag "sbt" (and the name of the sbt plugin(s) if any).

- State the problem or question clearly and provide enough context. Code examples and `build.sbt` are often useful when appropriately edited.
- There's also [Gitter sbt/sbt room][gitter], but Stackoverflow is recommended so others can benefit from the answers.

For professional support, for instance if you need faster response times, [Lightbend], the maintainer of Scala compiler and sbt, provides:

- [Lightbend Subscriptions][subscriptions], which includes Expert Support
- Training
- Consulting

How to contribute to sbt
========================

There are lots of ways to contribute to sbt ecosystem depending on your interests and skill level.

- Help someone at work or online help their build problem.
- Answer StackOverflow questions.
- Create plugins that extends sbt's feature.
- Maintain and update [documentation].
- Garden the issue tracker.
- Report issues.
- Patch the core (send pull requests to code).
- On-ramp other contributors.

Issues and Pull Requests
------------------------

When you find a bug in sbt we want to hear about it. Your bug reports play an important part in making sbt more reliable and usable.

Effective bug reports are more likely to be fixed. These guidelines explain how to write such reports and pull requests.

Please open a GitHub issue when you are 90% sure it's an actual bug.

If you have an enhancement idea, or a general discussion, bring it up to [sbt-contrib].

### Notes about Documentation

Documentation fixes and contributions are as much welcome as to patching the core. Visit [sbt/website][documentation] to learn about how to contribute.

### Preliminaries

- Make sure your sbt version is up to date.
- Search [StackOverflow] and [Issues] to see whether your bug has already been reported.
- Open one case for each problem.
- Proceed to the next steps for details.

### What to report

The developers need three things from you: **steps**, **problems**, and **expectations**.

#### Steps

The most important thing to remember about bug reporting is to clearly distinguish facts and opinions. What we need first is **the exact steps to reproduce your problems on our computers**. This is called *reproduction steps*, which is often shortened to "repro steps" or "steps." Describe your method of running sbt. Provide `build.sbt` that caused the problem and the version of sbt or Scala that was used. Provide sample Scala code if it's to do with incremental compilation. If possible, minimize the problem to reduce non-essential factors.

Repro steps are the most important part of a bug report. If we cannot reproduce the problem in one way or the other, the problem can't be fixed. Telling us the error messages is not enough.

#### Problems

Next, describe the problems, or what *you think* is the problem. It might be "obvious" to you that it's a problem, but it could actually be an intentional behavior for some backward compatibility etc. For compilation errors, include the stack trace. The more raw info the better.

#### Expectations

Same as the problems. Describe what *you think* should've happened.

#### Notes

Add any optional notes section to describe your analysis.

### Subject

The subject of the bug report doesn't matter. A more descriptive subject is certainly better, but a good subject really depends on the analysis of the problem, so don't worry too much about it. "StackOverflowError while name hashing is enabled" is good enough.

### Formatting

If possible, please format code or console outputs.

On Github it's:

    ```scala
    name := "foo"
    ```

On StackOverflow, it's:

```
<!-- language: lang-scala -->

    name := "foo"
```

Here's a simple sample case: [#327][327].
Finally, thank you for taking the time to report a problem.

Pull Requests
-------------

See below for the branch to work against.

### Adding notes

All pull requests are required to include a "Notes" file which documents the change.  This file should reside in the
directory:

    <sbt root>
      notes/
        <target release>/
           <your-change-name>.md

Notes files should have the following contents:

* Bullet item description under one of the following sections:
  - `### Bug fixes`
  - `### Improvements`
  - `### Fixes with compatibility implications`
* Complete section describing new features.

### Clean history

Make sure you document each commit and squash them appropriately. You can use the following guides as a reference:

* Scala's documentation on [Git Hygiene](https://github.com/scala/scala/tree/v2.12.0-M3#git-hygiene)
* Play's documentation on [Working with Git](https://www.playframework.com/documentation/2.4.4/WorkingWithGit#Squashing-commits)

Build from source
=================

### Branch to work against

sbt uses two branches for development:

- Development branch: `1.x` (this is also called "master")
- Stable branch: `1.$MINOR.x`, where `$MINOR` is current minor version (e.g. `1.1.x` during 1.1.x series)

If you're working on a bug fix, it's a good idea to start with the `1.$MINOR.x` branch, since we can always safely merge from stable to `1.x`, but not other way around.

### Instruction to build all modules from source

1. Install the current stable binary release of sbt (see [Setup]), which will be used to build sbt from source.
2. Get the source code.

   ```
   $ mkdir sbt-modules
   $ cd sbt-modules
   $ for i in sbt io util librarymanagement zinc; do \
     git clone https://github.com/sbt/$i.git && (cd $i; git checkout -b 1.1.x origin/1.1.x)
   done
   $ cd sbt
   $ ./sbt-allsources.sh
   ```

3. To build and publish all components locally,

   ```
   $ ./sbt-allsources.sh
   sbt:sbtRoot> publishLocalAllModule
   ```

### Instruction to build just sbt

If the change you are making is contained in sbt/sbt, you could publishLocal on sbt/sbt:

```
$ sbt
sbt:sbtRoot> publishLocal
```

### Using the locally built sbt

The `publishLocal` above will build and publish version `1.$MINOR.$PATCH-SNAPSHOT` (e.g. 1.1.2-SNAPSHOT) to your local ivy repository.

To use the locally built sbt, set the version in `build.properties` file in your project to `1.$MINOR.$PATCH-SNAPSHOT` then launch `sbt` (this can be the `sbt` launcher installed in your machine).

```
$ cd $YOUR_OWN_PROJECT
$ sbt
> compile
```

### Clearing out boot and local cache

When you run a locally built sbt, the JAR artifacts will be now cached under `$HOME/.sbt/boot/scala-2.12.4/org.scala-sbt/sbt/1.$MINOR.$PATCH-SNAPSHOT` directory. To clear this out run: `reboot dev` command from sbt's session of your test application.

One drawback of `-SNAPSHOT` version is that it's slow to resolve as it tries to hit all the resolvers. You can workaround that by using a version name like `1.$MINOR.$PATCH-LOCAL1`. A non-SNAPSHOT artifacts will now be cached under `$HOME/.ivy/cache/` directory, so you need to clear that out using [sbt-dirty-money](https://github.com/sbt/sbt-dirty-money)'s `cleanCache` task.

### Diagnosing build failures

Globally included plugins can interfere building `sbt`; if you are getting errors building sbt, try disabling all globally included plugins and try again.

### Running Tests

sbt has a suite of unit tests and integration tests, also known as scripted tests.

#### Unit / Functional tests

Various functional and unit tests are defined throughout the
project. To run all of them, run `sbt test`. You can run a single test
suite with `sbt testOnly`

#### Integration tests

Scripted integration tests reside in `sbt/src/sbt-test` and are
written using the same testing infrastructure sbt plugin authors can
use to test their own plugins with sbt. You can read more about this
style of tests [here](http://www.scala-sbt.org/1.0/docs/Testing-sbt-plugins).

You can run the integration tests with the `sbt scripted` sbt
command. To run a single test, such as the test in
`sbt/src/sbt-test/project/global-plugin`, simply run:

    sbt "scripted project/global-plugin"

Profiling sbt
-------------

There are several ways to profile sbt. The new hotness in profiling is FlameGraph.
You first collect stack trace samples, and then it is processed into svg graph.
See:

- [Using FlameGraphs To Illuminate The JVM by Nitsan Wakart](https://www.youtube.com/watch?v=ugRrFdda_JQ)
- [USENIX ATC '17: Visualizing Performance with Flame Graphs](https://www.youtube.com/watch?v=D53T1Ejig1Q)

### jvm-profiling-tools/async-profiler

The first one I recommend is async-profiler. This is available for macOS and Linux,
and works fairly well.

1. Download the installer from https://github.com/jvm-profiling-tools/async-profiler/releases/tag/v1.2
2. Make symbolic link to `build/` and `profiler.sh` to `$HOME/bin`, assuming you have PATH to `$HOME/bin`:
   `ln -s ~/Applications/async-profiler/profiler.sh $HOME/bin/profiler.sh`
   `ln -s ~/Applications/async-profiler/build $HOME/bin/build`

Next, close all Java appliations and anything that may affect the profiling, and run sbt in one terminal:

```
$ sbt exit
```

In another terminal, run:

```
$ jps
92746 sbt-launch.jar
92780 Jps
```

This tells you the process ID of sbt. In this case, it's 92746. While it's running, run

```
$ profiler.sh -d 60 <process id>
Started [cpu] profiling
--- Execution profile ---
Total samples:         31602
Non-Java:              3239 (10.25%)
GC active:             46 (0.15%)
Unknown (native):      14667 (46.41%)
Not walkable (native): 3 (0.01%)
Unknown (Java):        433 (1.37%)
Not walkable (Java):   8 (0.03%)
Thread exit:           1 (0.00%)
Deopt:                 9 (0.03%)

Frame buffer usage:    55.658%

Total: 1932000000 (6.11%)  samples: 1932
  [ 0] java.lang.ClassLoader$NativeLibrary.load
  [ 1] java.lang.ClassLoader.loadLibrary0
  [ 2] java.lang.ClassLoader.loadLibrary
  [ 3] java.lang.Runtime.loadLibrary0
  [ 4] java.lang.System.loadLibrary
....
```

This should show a bunch of stacktraces that are useful.
To visualize this as a flamegraph, run:

```
$ profiler.sh -d 60 -f /tmp/flamegraph.svg <process id>
```

This should produce `/tmp/flamegraph.svg` at the end.

![flamegraph](project/flamegraph_svg.png)

See https://gist.github.com/eed3si9n/82d43acc95a002876d357bd8ad5f40d5

### running sbt with standby

One of the tricky things you come across while profiling is figuring out the process ID,
while wnating to profile the beginning of the application.

For this purpose, we've added `sbt.launcher.standby` JVM flag.
In the next version of sbt, you should be able to run:

```
$ sbt -J-Dsbt.launcher.standby=20s exit
```

This will count down for 20s before doing anything else.

### jvm-profiling-tools/perf-map-agent

If you want to try the mixed flamegraph, you can try perf-map-agent.
This uses `dtrace` on macOS and `perf` on Linux.

You first have to compile https://github.com/jvm-profiling-tools/perf-map-agent.
For macOS, here to how to export `JAVA_HOME` before running `cmake .`:

```
$ export JAVA_HOME=$(/usr/libexec/java_home)
$ cmake .
-- The C compiler identification is AppleClang 9.0.0.9000039
-- The CXX compiler identification is AppleClang 9.0.0.9000039
...
$ make
```

In addition, you have to git clone https://github.com/brendangregg/FlameGraph

In a fresh termimal, run sbt with `-XX:+PreserveFramePointer` flag:

```
$ sbt -J-Dsbt.launcher.standby=20s -J-XX:+PreserveFramePointer exit
```

In the terminal that you will run the perf-map:

```
$ cd quicktest/
$ export JAVA_HOME=$(/usr/libexec/java_home)
$ export FLAMEGRAPH_DIR=$HOME/work/FlameGraph
$ jps
94592 Jps
94549 sbt-launch.jar
$ $HOME/work/perf-map-agent/bin/dtrace-java-flames 94549
dtrace: system integrity protection is on, some features will not be available

dtrace: description 'profile-99 ' matched 2 probes
Flame graph SVG written to DTRACE_FLAME_OUTPUT='/Users/xxx/work/quicktest/flamegraph-94549.svg'.
```

This would produce better flamegraph in theory, but the output looks too messy for `sbt exit` case.
See https://gist.github.com/eed3si9n/b5856ff3d987655513380d1a551aa0df
This might be because it assumes that the operations are already JITed.

### ktoso/sbt-jmh

https://github.com/ktoso/sbt-jmh

Due to JIT warmup etc, benchmarking is difficult. JMH runs the same tests multiple times to
remove these effects and comes closer to measuring the performance of your code.

There's also an integration with jvm-profiling-tools/async-profiler, apparently.

### VisualVM

I'd also mention traditional JVM profiling tool. Since VisualVM is opensource,
I'll mention this one: https://visualvm.github.io/

1. First VisualVM.
2. Start sbt from a terminal.
3. You should see `xsbt.boot.Boot` under Local.
4. Open it, and select either sampler or profiler, and hit CPU button at the point when you want to start.

If you are familiar with YourKit, it also works similarly.

Other notes for maintainers
---------------------------

### Publishing VS Code Extensions


https://code.visualstudio.com/docs/extensions/publish-extension

```
$ sbt
> vscodePlugin/compile
> exit
cd vscode-sbt-scala/client
# update version number in vscode-sbt-scala/client/package.json
$ vsce package
$ vsce publish
```

## Signing the CLA

Contributing to sbt requires you or your employer to sign the
[Lightbend Contributor License Agreement](https://www.lightbend.com/contribute/cla).

To make it easier to respect our license agreements, we have added an sbt task
that takes care of adding the LICENSE headers to new files. Run `headerCreate`
and sbt will put a copyright notice into it.