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<!DOCTYPE html>
<html lang="en">
<!--
Copyright 2014 Pants project contributors (see CONTRIBUTORS.md).
Licensed under the Apache License, Version 2.0 (see LICENSE).
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<head>
<meta charset="utf-8"/>
<title>Developing a Pants Plugin</title>
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<ul>
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Getting Started
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<a href="install.html">Installing Pants</a>
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Pants Basics
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Code & Doc Generation
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<a href="grpcio_gen.html">Python gRPC + protobufs</a>
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Getting Help
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Reference
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<a href="notes-1.30.x.html">1.30.x Stable Releases</a>
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<a href="notes-1.29.x.html">1.29.x Stable Releases</a>
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<a href="notes-1.26.x.html">1.26.x Stable Releases</a>
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<a href="notes-1.25.x.html">1.25.x Stable Releases</a>
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<a href="notes-1.23.x.html">1.23.x Stable Releases</a>
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<a href="notes-1.22.x.html">1.22.x Stable Releases</a>
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<a href="notes-1.21.x.html">1.21.x Stable Releases</a>
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<a href="notes-1.20.x.html">1.20.x Stable Releases</a>
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<a href="notes-1.19.x.html">1.19.x Stable Releases</a>
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<a href="notes-1.18.x.html">1.18.x Stable Releases</a>
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<a href="notes-1.17.x.html">1.17.x Stable Releases</a>
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<a href="notes-1.16.x.html">1.16.x Stable Releases</a>
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<a href="notes-1.15.x.html">1.15.x Stable Releases</a>
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<a href="notes-1.14.x.html">1.14.x Stable Releases</a>
</li>
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<a href="notes-1.13.x.html">1.13.x Stable Releases</a>
</li>
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<a href="notes-1.12.x.html">1.12.x Stable Releases</a>
</li>
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<a href="notes-1.11.x.html">1.11.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.10.x.html">1.10.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.9.x.html">1.9.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.8.x.html">1.8.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.7.x.html">1.7.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.6.x.html">1.6.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.5.x.html">1.5.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.4.x.html">1.4.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.3.x.html">1.3.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.2.x.html">1.2.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.1.x.html">1.1.x Stable Releases</a>
</li>
<li class="toc-h1 toc-link ">
<a href="notes-1.0.x.html">1.0.x Stable Releases</a>
</li>
</ul>
</li>
<li class="toc-h1 toc-heading">
Developer
</li>
<li class="toc-h1 toc-link ">
<a href="dev.html">Pants Developer Center</a>
</li>
<li class="toc-h1 toc-link ">
<a href="export.html">Export Format</a>
</li>
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<a href="architecture.html">Architecture</a>
</li>
<li class="toc-h1 toc-heading">
Blogs
</li>
<li class="toc-h1 toc-link ">
<a href="coursier_migration.html">Twitter's Coursier Migration</a>
</li>
</ul>
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<div class="col-md-8">
<div class="content">
<div class="mainflow">
<nav class="pagetoc">
<ul>
<li class="toc-h1"><a href="#a-hello-world-plugin">A "Hello World" plugin</a></li>
<li class="toc-h1"><a href="#simple-configuration">Simple Configuration</a></li>
<li class="toc-h1"><a href="#examples-from-twittercommons">Examples from twitter/commons</a></li>
</ul>
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<!-- main content start -->
<!-- generated by pants! -->
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<h1 id="developing-a-pants-plugin">Developing a Pants Plugin</h1>
<p>This page documents how to develop a Pants plugin, a set of code that
defines new Pants functionality. If you
<a href="dev_tasks.html">develop a new task</a>
or target to add to Pants (or to
override an existing part of Pants), a plugin gives you a way to
register your code with Pants.</p>
<p>Much of Pants' own functionality is organized in plugins; see them in
<a href="https://github.com/pantsbuild/pants/tree/master/src/python/pants/backend"><code>src/python/pants/backend/*</code></a>.</p>
<p>A plugin registers its functionality with Pants by defining some
functions in a <code>register.py</code> file in its top directory. For example,
Pants' <code>jvm</code> code registers in
<a href="https://github.com/pantsbuild/pants/blob/master/src/python/pants/backend/jvm/register.py">src/python/pants/backend/jvm/register.py</a>
Pants' backend-loader code assumes your plugin has a <code>register.py</code> file
there.</p>
<h2 id="a-hello-world-plugin">A "Hello World" plugin</h2>
<p>This "Hello World" plugin example shows how to register a plugin with Pants. It defines a new
<code>hello-world</code> goal with two tasks. Here's how to create it:</p>
<ul>
<li>
<p>If you don't have an existing Pants project to work with, create one. Locate its config file,
typically <code>pants.toml</code> in the repo root.</p>
</li>
<li>
<p>Create a directory for your plugins. In this example we will use the <code>plugins/</code> directory in
the repo root, but there is no convention, and you can put them wherever you like.</p>
</li>
<li>
<p>In the <code>plugins/</code> directory, create following filesystem structure:</p>
<div class="codehilite"><pre><span></span>hello/
__init__.py
register.py
tasks/
__init__.py
your_tasks.py
</pre></div>
</li>
<li>
<p><code>__init__.py</code> files can be empty - you're just saying to Python that you created modules.</p>
</li>
<li>
<p>In <code>your_tasks.py</code> place the following content:</p>
<div class="codehilite"><pre><span></span><span class="kn">from</span> <span class="nn">pants.task.task</span> <span class="kn">import</span> <span class="n">Task</span>
<span class="k">class</span> <span class="nc">HelloTask</span><span class="p">(</span><span class="n">Task</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">execute</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"Hello"</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">WorldTask</span><span class="p">(</span><span class="n">Task</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">execute</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"world!"</span><span class="p">)</span>
</pre></div>
</li>
</ul>
<p><a href="https://github.com/pantsbuild/pants/blob/master/src/python/pants/task/task.py">Task</a> is a simple base
class for your tasks - you must implement the <code>execute</code> method.</p>
<ul>
<li>In <code>register.py</code> place the following content:<div class="codehilite"><pre><span></span><span class="kn">from</span> <span class="nn">pants.goal.goal</span> <span class="kn">import</span> <span class="n">Goal</span>
<span class="kn">from</span> <span class="nn">pants.goal.task_registrar</span> <span class="kn">import</span> <span class="n">TaskRegistrar</span> <span class="k">as</span> <span class="n">task</span>
<span class="kn">from</span> <span class="nn">hello.tasks.your_tasks</span> <span class="kn">import</span> <span class="n">HelloTask</span><span class="p">,</span> <span class="n">WorldTask</span>
<span class="k">def</span> <span class="nf">register_goals</span><span class="p">():</span>
<span class="n">Goal</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s2">"hello-world"</span><span class="p">,</span> <span class="n">description</span><span class="o">=</span><span class="s2">"Say hello to your world"</span><span class="p">)</span>
<span class="n">task</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s1">'hello'</span><span class="p">,</span> <span class="n">action</span><span class="o">=</span><span class="n">HelloTask</span><span class="p">)</span><span class="o">.</span><span class="n">install</span><span class="p">(</span><span class="s1">'hello-world'</span><span class="p">)</span>
<span class="n">task</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s1">'world'</span><span class="p">,</span> <span class="n">action</span><span class="o">=</span><span class="n">WorldTask</span><span class="p">)</span><span class="o">.</span><span class="n">install</span><span class="p">(</span><span class="s1">'hello-world'</span><span class="p">)</span>
</pre></div>
</li>
</ul>
<p>This creates a new goal named <code>hello-world</code>, and registers the two tasks to it.</p>
<ul>
<li>In <code>pants.toml</code> place the following content:<div class="codehilite"><pre><span></span><span class="k">[GLOBAL]</span>
<span class="n">pants_version</span> <span class="o">=</span> <span class="s">"1.26.0"</span>
<span class="n">pythonpath</span> <span class="o">=</span> <span class="k">["%(buildroot)s/plugins"]</span>
<span class="n">backend_packages</span> <span class="o">=</span> <span class="k">["hello"]</span>
</pre></div>
</li>
</ul>
<p><code>backend_packages</code> defines which plugins you want to use in your project.</p>
<p>If you want to use custom plugins directly from source when building in the same repo, you need
to put them on the <code>pythonpath</code> so Pants can find them. </p>
<ul>
<li>You are ready to use your plugin! First try to find your goal by typing <code>./pants goals</code>:<div class="codehilite"><pre><span></span>...
hello-world: Say hello to your world
...
</pre></div>
</li>
</ul>
<p>Now you can use your plugin by typing <code>./pants hello-world</code>:</p>
<div class="codehilite"><pre><span></span> ::
...
Executing tasks in goals: hello-world
XX:XX:XX 00:00 [hello-world]
XX:XX:XX 00:00 [hello]Hello
XX:XX:XX 00:00 [world]world!
XX:XX:XX 00:00 [complete]
SUCCESS
</pre></div>
<p>Note that to consume the custom plugin as a published artifact (say on PyPI), instead of
directly from the repo, then instead of <code>backend_packages</code> and <code>pythonpath</code> you would set <code>plugins</code>:</p>
<div class="codehilite"><pre><span></span> :::toml
[GLOBAL]
pants_version = "1.26.0"
plugins = ["myorg.hello==1.7.6"]
</pre></div>
<p>Similarly, if your custom plugin is consumed directly from the repo, but has dependencies on
published artifacts, then you list those in <code>plugins</code>:</p>
<div class="codehilite"><pre><span></span> :::toml
[GLOBAL]
pants_version = "1.26.0"
pythonpath = ["%(buildroot)s/plugins"]
backend_packages = ["hello"]
plugins = ["some.dependency==4.5.11"]
</pre></div>
<p>See below for more details. </p>
<h2 id="simple-configuration">Simple Configuration</h2>
<p>If you want to extend Pants without adding any 3rd-party libraries that aren't already referenced by
Pants, you can use the following technique using sources stored directly in your repo.
All you need to do is name the package where the plugin is defined, and the pythonpath entry to
load it from.</p>
<p>In the example below, the stock <code>JvmBinary</code> target is subclassed so that a custom task (not shown)
can consume it specifically but disregard regular <code>JvmBinary</code> instances (using <code>isinstance()</code>).</p>
<ul>
<li>
<p>Define a home for your plugins. In this example we'll use a top-level <code>plugins/</code> directory but
this is not special.</p>
</li>
<li>
<p>Create an empty <code>plugins/hadoop/targets/__init__.py</code> to define a python package structure
for your custom hadoop target type plugin. Also create empty <code>__init__.py</code> files in each
directory up to but not including the root directory of your python package layout; in this case,
just <code>plugins/hadoop/__init__.py</code>.</p>
</li>
<li>
<p>Create a python module for your custom target type in <code>plugins/hadoop/targets/hadoop_binary.py</code>:</p>
<div class="codehilite"><pre><span></span><span class="c1"># plugins/hadoop/targets/hadoop_binary.py</span>
<span class="kn">from</span> <span class="nn">pants.backend.jvm.targets.jvm_binary</span> <span class="kn">import</span> <span class="n">JvmBinary</span>
<span class="k">class</span> <span class="nc">HadoopBinary</span><span class="p">(</span><span class="n">JvmBinary</span><span class="p">):</span>
<span class="k">pass</span>
</pre></div>
</li>
<li>
<p>Create <code>plugins/hadoop/register.py</code> to register the elements exposed by your plugin to BUILD file
authors:</p>
<div class="codehilite"><pre><span></span><span class="c1"># plugins/hadoop/register.py</span>
<span class="kn">from</span> <span class="nn">pants.build_graph.build_file_aliases</span> <span class="kn">import</span> <span class="n">BuildFileAliases</span>
<span class="kn">from</span> <span class="nn">hadoop.targets.hadoop_binary</span> <span class="kn">import</span> <span class="n">HadoopBinary</span>
<span class="k">def</span> <span class="nf">build_file_aliases</span><span class="p">():</span>
<span class="k">return</span> <span class="n">BuildFileAliases</span><span class="p">(</span>
<span class="n">targets</span><span class="o">=</span><span class="p">{</span>
<span class="c1"># NB: This allows a HadoopBinary target to be created in a BUILD file using the</span>
<span class="c1"># hadoop_binary alias.</span>
<span class="s1">'hadoop_binary'</span><span class="p">:</span> <span class="n">HadoopBinary</span><span class="p">,</span>
<span class="p">},</span>
<span class="p">)</span>
</pre></div>
</li>
<li>
<p>In <code>pants.toml</code>, add your new plugin package to the list of backends to load when pants starts.
This instructs pants to load a module named <code>hadoop.register</code>.</p>
<div class="codehilite"><pre><span></span><span class="k">[GLOBAL]</span>
<span class="n">pythonpath</span> <span class="o">=</span> <span class="k">['%(buildroot)s/plugins']</span>
<span class="n">backend_packages</span> <span class="o">=</span> <span class="k">['hadoop']</span>
</pre></div>
</li>
</ul>
<p>Note that you can also set the PYTHONPATH in your <code>./pants</code> wrapper script, instead of in
<code>pants.toml</code>, if you have other reasons to do so. Either way, pants will look for a <code>register.py</code>
file for each backend package you list by prefixing that package with the python path; ie roughly
<code>pythonpath + backend package + register.py</code> is tried for each pythonpath prefix until a
<code>register.py</code> is found, in this example <code>plugins/hadoop/register.py</code>.</p>
<h2 id="examples-from-twittercommons">Examples from <code>twitter/commons</code></h2>
<p>For an example of a code repo with plugins to add features to Pants when building in that repo,
take a look at <a href="https://github.com/twitter/commons"><code>twitter/commons</code></a>, especially its
<a href="https://github.com/twitter/commons/tree/32011ab5351fea23e8c70e24e752540b06d1389f/pants-plugins"><code>pants-plugins</code> directory</a>.</p>
<p>The repo's <a href="https://github.com/twitter/commons/blob/32011ab5351fea23e8c70e24e752540b06d1389f/pants.ini"><code>pants.ini</code> file</a> (the format used before <code>pants.toml</code>) has a
<code>backend_packages</code> entry listing the plugin packages (packages with <code>register.py</code> files):</p>
<div class="codehilite"><pre><span></span><span class="k">[GLOBAL]</span>
<span class="na">pythonpath: [</span>
<span class="na">"%(buildroot)s/pants-plugins/src/python",</span>
<span class="na">]</span>
<span class="na">backend_packages: [</span>
<span class="na">'twitter.common.pants.jvm.extras',</span>
<span class="na">'twitter.common.pants.python.commons',</span>
<span class="na">'pants.contrib.python.checks',</span>
<span class="na">]</span>
</pre></div>
<p>The <a href="https://github.com/twitter/commons/blob/master/pants-plugins/src/python/twitter/common/pants/jvm/extras/register.py"><code>...jvm/extras/register.py</code></a>
file registers a <code>checkstyle</code> goal. To find the code for this task, come back to the
<code>pantsbuild/pants</code> repo: Pants defines the
<a href="https://github.com/pantsbuild/pants/blob/master/src/python/pants/backend/jvm/tasks/checkstyle.py"><code>Checkstyle</code> task class</a> but doesn't register it.
But other Pants workspaces can register it, as <code>twitter/commons</code> illustrates.</p>
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