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# How To Use Apache Yetus with Apache HBase

This document describes how to get up and running with [Apache Yetus][yetus],
as pertains to the development of Apache HBase. Specifically this covers the use
of `test-patch`, of which HBase developers make use for tasks related to code
quality. These are normally run via automation in the foundation's
[Build][builds] infrastructure. They can also be run locally, which is the
subject of this document.

The Yetus project provides its own documentation of `test-patch` in
[Basic PreCommit][yetus-basic-precommit]. By comparison, this document is
intended to be highly abbreviated, hands-on, and focused on the HBase use-case.
See that document for more complete explanations and further details.

## Installation

In order to run Yetus, you'll need to first install Yetus and its dependencies.
This is somewhat simplified when used in Docker mode. Yetus can be retrieved
from a [distribution artifact][yetus-downloads]. Homebrew/Linuxbrew users can
install from the tap, the process for which is also described on the downloads
page.

# Usage Basics

Apache Yetus is comprised of a number of different components. The focus of our
interest is `test-patch`. `test-patch` is a modular system. Many modules depend
on some external tool to provide the underlying functionality. For example, the
`compile` check delegates to a number of provider modules, for example `maven`
or `gradle` for JVM projects. In order to use these modules, those tools must
be installed. Yetus calls these modules "plugins".

To see a list of all plugins available to `test-patch`, use

```shell script
$ test-patch --list-plugins
```

To see a list of all the options available in both the core modules as well as
all the plugins, use

```shell script
$ test-patch --plugins=all --help
```

An invocation of `test-patch` requires use of one or more plugins. Often times,
when the full suite of checks are run, specify the meta-plugin "all". Otherwise,
a limited selection of plugins can be selected using the `--plugins` argument.

## The Workspace, The Patch

`test-patch` operates within a "workspace," a checkout from a source control
repository. It has a number of options pertaining to this workspace, such as
the path to the workspace (`--basedir`) and whether it will permit the presence
of uncommitted changes therein (`--dirty-workspace`).

Onto this workspace, it can optionally apply a change, a.k.a., the "patch" in
"test patch." The patch can come from a number of sources, including a patch
file, a JIRA ID, a Pull Request, &c. Or, explicitly inform Yetus that no patch
file is provided, and the repository should be checked as is, by passing
`--empty-patch`.

## Personalities

`test-patch` is extremely extensible. Even the functionality of its core
modules can be extended or overridden. It allows for this type of
"personalization" by way of "personality" overrides. Yetus ships a number of
these personalities; a pre-packaged personality can be selected via the
`--project` parameter. There is a provided HBase personality in Yetus, however
the HBase project maintains its own within the HBase source repository. Specify
the path to the personality file using `--personality`. The HBase repository
places this file under `dev-support/hbase-personality.sh`. 

## Docker mode

Running Yetus in Docker mode simplifies the concerns of dependencies because
the provided `Dockerfile` handles their installation automatically. However,
for MacOS users, there are a number of known issues with running Docker on OSX,
so it may be preferable to instead run outside of the container.

To run in Docker, of course you must install `docker` or some container runtime
equivalent. [Docker Desktop][docker-desktop] is an option for Mac and Windows
users.

When running `test-patch` with HBase in docker mode, two parameters must be
provided. `--docker` activates the `docker` module, enabling the feature.
Additionally, `--dockerfile` points Yetus at HBase's provided `Dockerfile`,
instead of using the one provided out-of-the-box by Yetus. The HBase repository
places this file under `dev-support/docker/Dockerfile`.

## JVM and JAVA_HOME

HBase supports compilation and test execution on a number of different JVM
versions. To facilitate this, the `Dockerfile` installs multiple JVMs. An
invocation of `test-patch` requires additional parameters in order to specify
the target JVM. How you do this is slightly different based on whether you run
with or without Docker mode.

### Setting `JAVA_HOME` Outside of Docker Mode

Simply specify `JAVA_HOME` in the environment in which `test-patch` is launched.

### Setting `JAVA_HOME` Inside of Docker Mode

The docker image JDKs are available under `/usr/lib/jvm`. Symlinks are provided
for each supported major version, i.e., `java-11`. Use the `test-patch` argument
`--java-home`.

# Example: Run SpotBugs

One of the checks supported by Yetus is the static analysis tool
[SpotBugs][spotbugs]. Let's put together all the above and run SpotBugs with
`test-patch`.

The SpotBugs check depends on a SpotBugs installation. This is provided by the
docker file. For running without docker, you'll need to download and unpack the
SpotBugs binary distribution.

Running the SpotBugs check also depends on [Apache Maven][maven], the build
system used by HBase. In order for the check to function, both the `maven`
and `spotbugs` plugins must be specified. If this dependency is omitted, Yetus
will error with a message similar to

```
ERROR: you can't specify maven as the buildtool if you don't enable the plugin.
```

To run just the SpotBugs check, we must explicitly specify `spotbugs` and its
dependency using `--plugins=maven,spotbugs`.

## Without Docker

Putting it all together, without using docker:

```shell script
$ cd /path/to/hbase
$ JAVA_HOME=/path/to/jdk-8 test-patch.sh \
  --plugins=maven,spotbugs \
  --spotbugs-home=/path/to/spotbugs/
  --dirty-workspace \
  --empty-patch \
  --personality=./dev-support/hbase-personality.sh
```

## With Docker

Putting it all together, using docker:

```shell script
$ cd /path/to/hbase
$ test-patch.sh \
  --plugins=maven,spotbugs \
  --dirty-workspace \
  --empty-patch \
  --personality=./dev-support/hbase-personality.sh \
  --docker \
  --dockerfile=./dev-support/docker/Dockerfile \
  --java-home=/usr/lib/jvm/java-8
```

[builds]: https://builds.apache.org
[docker-desktop]: https://www.docker.com/products/docker-desktop
[maven]: https://maven.apache.org
[spotbugs]: https://spotbugs.github.io
[yetus]: https://yetus.apache.org
[yetus-basic-precommit]: https://yetus.apache.org/documentation/in-progress/precommit-basic/
[yetus-downloads]: https://yetus.apache.org/downloads/