docs/concept/visibility.soy

{namespace buck.visibility}

/***/
{template .soyweb}
  {call buck.page}
    {param title: 'Visibility' /}
    {param prettify: true /}
    {param content}

Visibility determines whether a build rule can include a build target in its
list of <code>deps</code>. In a large project, you may want to prevent
developers from "reaching across" the project and pulling in additional code.
Reducing the visibility of a build rule can help prevent that type of behavior. 
<p>
Build rules are visible to the other targets inside the same build file
by default.
<p>
To make a build rule visible to other targets, add a <code>visibility</code>{sp}
argument to the build rule and provide a list of
{sp}<a href="{ROOT}concept/build_target_pattern.html">build target patterns</a>.
<p>
There is also a special value, <code>'PUBLIC'</code>, which makes a build rule
visible to all other rules.
<h2>Examples</h2>

A common library like Guava should be able to be included by any build rule:

{literal}<pre class="prettyprint lang-py">
prebuilt_jar(
  name = 'guava',
  binary_jar = 'guava-14.0.1.jar',
  visibility = [
    'PUBLIC',
  ],
)
</pre>{/literal}

It is common to restrict the visibility of Android resources to the Java
code that uses it:

{literal}<pre class="prettyprint lang-py">
android_resource(
  name = 'ui_res',
  res = 'res',
  package = 'com.example',
  visibility = [
    '//java/com/example/ui:ui',
  ],
)
</pre>{/literal}

Or it may be simpler to make it visible to the entire directory in case
additional build rules are added to <code>java/com/example/ui/BUCK</code>:

{literal}<pre class="prettyprint lang-py">
android_resource(
  name = 'ui_res',
  res = 'res',
  package = 'com.example',
  visibility = [
    '//java/com/example/ui:',
  ],
)
</pre>{/literal}

Finally, it is common to limit code for testing to be visible only to tests.
If you define all of your Java unit tests in a folder named
{sp}<code>javatests/</code> in the root of your project, then you could
define the following rule to ensure that only allow build rules
under <code>javatests/</code> can depend on JUnit:

{literal}<pre class="prettyprint lang-py">
prebuilt_jar(
  name = 'junit',
  binary_jar = 'junit-4.11.jar',
  visibility = [
    '//javatests/...',
  ],
)
</pre>{/literal}

    {/param}
  {/call}
{/template}