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<h1 id="scala-support">Scala Support</h1>
<h2 id="examples">Examples</h2>
<p>The sample code
<a href="https://github.com/pantsbuild/pants/blob/master/examples/src/scala/org/pantsbuild/example/hello/welcome/">examples/src/scala/org/pantsbuild/example/hello/welcome/</a>
shows how to define a library of Scala code.</p>
<p>Its <code>BUILD</code> file looks like that for a Java library, but contains a
<code>scala_library</code> target with <code>.scala</code> sources:</p>
<p>
<div class="md-included-snippet"><div class="codehilite"><pre><span class="n">scala_library</span><span class="p">(</span>
<span class="n">dependencies</span><span class="o">=</span><span class="p">[</span>
<span class="s">'examples/src/java/org/pantsbuild/example/hello/greet:greet'</span><span class="p">,</span>
<span class="s">'examples/src/resources/org/pantsbuild/example/hello'</span><span class="p">,</span>
<span class="p">],</span>
<span class="n">provides</span> <span class="o">=</span> <span class="n">scala_artifact</span><span class="p">(</span><span class="n">org</span><span class="o">=</span><span class="s">'org.pantsbuild.example.hello'</span><span class="p">,</span>
<span class="n">name</span><span class="o">=</span><span class="s">'welcome'</span><span class="p">,</span>
<span class="n">repo</span><span class="o">=</span><span class="n">public</span><span class="p">,),</span>
<span class="p">)</span>
</pre></div></div>
</p>
<p>There's a sample test in
<a href="https://github.com/pantsbuild/pants/tree/master/examples/tests/scala/org/pantsbuild/example/hello/welcome">examples/tests/scala/org/pantsbuild/example/hello/welcome</a>.
It's a <a xref="bdict_junit_tests"><code>junit_tests</code></a> with <code>.scala</code> sources.</p>
<p>
<div class="md-included-snippet"><div class="codehilite"><pre><span class="n">junit_tests</span><span class="p">(</span>
<span class="n">dependencies</span><span class="o">=</span><span class="p">[</span>
<span class="s">'examples/src/scala/org/pantsbuild/example/hello/welcome:welcome'</span><span class="p">,</span>
<span class="s">'3rdparty:junit'</span><span class="p">,</span>
<span class="s">'3rdparty:scalatest'</span><span class="p">,</span>
<span class="p">],</span>
<span class="p">)</span>
</pre></div></div>
</p>
<h2 id="scalajava-circular-dependencies">Scala/Java Circular Dependencies</h2>
<p>Scala code and Java code can depend on each other. As long as the dependencies aren't circular,
<code>scala_library</code> targets can depend on <code>java_library</code> targets and vice versa. If the dependencies
<em>are</em> circular, you can set up targets to compile all of this code together. Assuming your <code>*.java</code>
and <code>*scala</code> files are in separate directories, you can have:</p>
<ul>
<li>a <code>java_library</code> whose <code>sources</code> param is the <code>*.java</code> files; one of its
dependencies should be...</li>
<li>a <code>scala_library</code> whose <code>sources</code> param is the <code>*.scala</code> files and
whose <code>java_sources</code> is the above <code>java_library</code>.</li>
</ul>
<p>Do not put the <code>java_library</code> in the <code>scala_library</code>'s <code>dependencies</code> or Pants will error out in its
circular dependencies check. Instead, put the <code>java_library</code> in <code>java_sources</code> to work around this
check.</p>
<p>The <a href="https://github.com/pantsbuild/pants/tree/master/examples/src/scala/org/pantsbuild/example/scala_with_java_sources"><code>scala_with_java_sources</code></a>
example shows how this works:</p>
<p>
<div class="md-included-snippet"><div class="codehilite"><pre><span class="n">scala_library</span><span class="p">(</span>
<span class="n">sources</span> <span class="o">=</span> <span class="p">[</span><span class="s">'Greet.scala'</span><span class="p">],</span>
<span class="n">java_sources</span><span class="o">=</span><span class="p">[</span>
<span class="s">'examples/src/java/org/pantsbuild/example/java_sources'</span><span class="p">,</span>
<span class="p">],</span>
<span class="p">)</span>
</pre></div></div>
</p>
<p>The referred-to
<a href="https://github.com/pantsbuild/pants/tree/master/examples/src/java/org/pantsbuild/example/java_sources/BUILD"><code>java_sources</code></a>
<code>java_library</code> has this <code>java_library</code> in its dependencies:</p>
<p>
<div class="md-included-snippet"><div class="codehilite"><pre><span class="n">java_library</span><span class="p">(</span>
<span class="n">dependencies</span> <span class="o">=</span> <span class="p">[</span>
<span class="s">'examples/src/scala/org/pantsbuild/example/scala_with_java_sources'</span><span class="p">,</span>
<span class="p">],</span>
<span class="p">)</span>
</pre></div></div>
</p>
<p>(If your circularly-referencing <code>*.scala</code> and <code>*.java</code> files are in the <em>same</em> directory, you don't
need separate <code>java_library</code> and <code>scala_library</code> targets. Instead, use
<code>scala_library(sources=globs('*.scala', '*.java'),...)</code>.)</p>
<h2 id="scala-version">Scala Version</h2>
<p>You can override the default version of the entire Scala toolchain with the single
<code>--scala-platform-version</code> option. You can set that option to one of the supported Scala versions
(currently "2.10" or "2.11"), or to the special value "custom".</p>
<p>If you choose a custom version, you must use the <code>--scala-platform-runtime-spec</code>,
<code>--scala-platform-repl-spec</code> and <code>--scala-platform-suffix-version</code> options to provide
information about your custom Scala version. The first two of these default to the target
addresses <code>//:scala-library</code> and <code>//:scala-repl</code> respectively, so you can simply define those
targets (in the root <code>BUILD.tools</code> file by convention) to point to the relevant JARs.</p>
<h2 id="scala-repl">Scala REPL</h2>
<p>To bring up Scala's interactive console, use Pants'
<a xref="oref_goal_repl"><code>repl</code></a> goal.
In the resulting console, you can <code>import</code> any Scala or Java code from the Pants invocation's
targets and their dependencies.</p>
<div class="codehilite"><pre>$ ./pants repl examples/src/scala/org/pantsbuild/example/hello/welcome
...much build output...
15:08:13 00:11 [resources]
15:08:13 00:11 [prepare]
Invalidated 1 target containing 1 payload file.
15:08:13 00:11 [repl]
15:08:13 00:11 [python-repl]
15:08:13 00:11 [scala-repl]
15:08:13 00:11 [bootstrap-scala-repl]
Welcome to Scala version 2.10.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_60).
Type in expressions to have them evaluated.
Type :help for more information.
scala> import org.pantsbuild.example.hello.welcome
import org.pantsbuild.example.hello.welcome
scala> val folks = List("Abel", "Baker", "Charlie", "Delta")
folks: List[java.lang.String] = List(Abel, Baker, Charlie, Delta)
scala> org.pantsbuild.example.hello.welcome.WelcomeEverybody(folks)
res0: Seq[String] = List(Hello, Abel!, Hello, Baker!, Hello, Charlie!, Hello, Delta!)
scala> exit
warning: there were 1 deprecation warnings; re-run with -deprecation for details
Waiting for background workers to finish.
SUCCESS
$
</pre></div>
<h2 id="testing">Testing</h2>
<p>Scala tests are run using the <code>junit_tests</code> BUILD target. Both Junit and ScalaTest tests are
supported by default. Most other scala test frameworks support running with JUnit via a base
class/trait or via a <code>@RunWith</code> annotation; so you can use
<code>junit_tests</code> for your scala tests as well.</p>
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