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<h1 class="page-title">Functions</h1>

{% dynamic setvar source_file "src/main/java/com/google/devtools/build/docgen/templates/be/functions.vm" %}
{% dynamic setvar version "8.3.0" %}
{% dynamic setvar original_path "/reference/be/functions" %}
{% include "_buttons.html" %}

<h2>Contents</h2>
<ul>
  <li><a href="#package">package</a></li>
  <li><a href="#package_group">package_group</a></li>
  <li><a href="#exports_files">exports_files</a></li>
  <li><a href="#glob">glob</a></li>
  <li><a href="#select">select</a></li>
  <li><a href="#subpackages">subpackages</a></li>
</ul>
<!-- =================================================================
                              package()
     =================================================================
-->

<h2 id="package">package</h2>

<pre>
package(default_deprecation, default_package_metadata, default_testonly, default_visibility, features)
</pre>
<p>This function declares metadata that applies to every rule in the
package. It is used at most once within a package (BUILD file).</p>

<p>For the counterpart that declares metadata applying to every rule in the whole
<em>repository</em>, use the <code>repo()</code> function in the
<a href="/versions/8.3.0/external/overview#repo.bazel"><code>REPO.bazel</code> file</a> at the root of your repo.
The <code>repo()</code> function takes exactly the same arguments as <code>package()</code>.</p>
<p>The package() function should be called right after all the load() statements at the top of the
file, before any rule.</p>

<h3 id="package_args">Arguments</h3>

<table class="table table-condensed table-bordered table-params">
  <colgroup>
    <col class="col-param" />
    <col class="param-description" />
  </colgroup>
  <thead>
    <tr>
      <th>Attribute</th>
      <th>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td id="package.default_applicable_licenses"><code>default_applicable_licenses</code></td>
      <td>
        <p>Alias for <a href="#package.default_package_metadata"><code>default_package_metadata</code></a>.
      </td>
    </tr>
    <tr>
      <td id="package.default_visibility"><code>default_visibility</code></td>
      <td>
        <p>List of <a href="/versions/8.3.0/concepts/labels">labels</a>; default is <code>[]</code></p>
        <p>The default visibility of the top-level rule targets and symbolic
        macros in this package &mdash; that is, the targets and symbolic macros
        that are not themselves declared inside a symbolic macro. This attribute
        is ignored if the target or macro specifies a <code>visibility</code>
        value.</p>
        <p>For detailed information about the syntax of this attribute, see the
        documentation of <a href="/versions/8.3.0/concepts/visibility">
        visibility</a>. The package default visibility does not apply to
        <a href="#exports_files">exports_files</a>, which is public by default.
        </p>
      </td>
    </tr>
    <tr>
      <td id="package.default_deprecation"><code>default_deprecation</code></td>
      <td>
        <p>String; default is <code>""</code></p>
        <p>Sets the default <a href="common-definitions.html#common.deprecation">
        <code>deprecation</code></a> message for all rules in this package.</p>
      </td>
    </tr>
    <tr>
      <td id="package.default_package_metadata"><code>default_package_metadata</code></td>
      <td>
        <p>List of <a href="/versions/8.3.0/concepts/labels">labels</a>; default is <code>[]</code></p>
        <p>Sets a default list of metadata targets which apply to all other targets in the package.
        These are typically targets related to OSS package and license declarations.
        See <a href="https://github.com/bazelbuild/rules_license">rules_license</a> for examples.</p>
      </td>
    </tr>
    <tr>
      <td id="package.default_testonly"><code>default_testonly</code></td>
      <td>
        <p>Boolean; default is <code>False</code> except as noted</p>
        <p>Sets the default <a href="common-definitions.html#common.testonly">
        <code>testonly</code></a> property for all rules in this package.</p>
        <p>In packages under <code>javatests</code> the default value is <code>True</code>.</p>
      </td>
    </tr>
    <tr>
      <td id="package.features"><code>features</code></td>
      <td>
        <p>List strings; default is <code>[]</code></p>
        <p>Sets various flags that affect the semantics of this BUILD file.</p>
        <p>This feature is mainly used by the people working on the build system to
        tag packages that need some kind of special handling. Do not use this unless
        explicitly requested by someone working on the build system.</p>

      </td>
    </tr>

  </tbody>
</table>

<h3 id="package_example">Examples</h3>

The declaration below declares that the rules in this package are
visible only to members of package
group <code>//foo:target</code>. Individual visibility declarations
on a rule, if present, override this specification.

<pre class="code">
package(default_visibility = ["//foo:target"])
</pre>

<!-- =================================================================
                              package_group()
     =================================================================
-->

<h2 id="package_group">package_group</h2>

<pre>package_group(name, packages, includes)</pre>

<p>This function defines a set of <a href="/versions/8.3.0/concepts/build-ref#packages">packages</a>
and associates a label with the set. The label can be referenced in
<code>visibility</code> attributes.</p>

<p>Package groups are primarily used for visibility control. A publicly visible
target can be referenced from every package in the source tree. A privately
visible target can only be referenced within its own package (not subpackages).
In between these extremes, a target may allow access to its own package plus any
of the packages described by one or more package groups. For a more detailed
explanation of the visibility system, see the
<a href="common-definitions.html#common.visibility">visibility</a>
attribute.</p>

<p>A given package is considered to be in the group if it either matches the
<code>packages</code> attribute, or is already contained in one of the other
package groups mentioned in the <code>includes</code> attribute.</p>

<p>Package groups are technically targets, but are not created by rules, and do
not themselves have any visibility protection.</p>

<h3 id="package_group_args">Arguments</h3>

<table class="table table-condensed table-bordered table-params">
  <colgroup>
    <col class="col-param" />
    <col class="param-description" />
  </colgroup>
  <thead>
    <tr>
      <th>Attribute</th>
      <th>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td id="package_group.name"><code>name</code></td>
      <td>
        <p><a href="/versions/8.3.0/concepts/labels#target-names">Name</a>; required</p>
        <p>A unique name for this target.</p>
      </td>
    </tr>
    <tr>
      <td id="package_group.packages"><code>packages</code></td>
      <td>
        <p>List of strings; default is <code>[]</code></p>
        <p>A list of zero or more package specifications.</p>

        <p>Each package specification string can have one of the following
        forms:</p>

        <ol>

        <li>The full name of a package, without its repository, starting with a
        double slash. For example, <code>//foo/bar</code> specifies the package
        having that name and which lives in the same repository as the package
        group.

        <li>As above, but with a trailing <code>/...</code>. For example, <code>
        //foo/...</code> specifies the set of <code>//foo</code> and all its
        subpackages. <code>//...</code> specifies all packages in the current
        repository.

        <li>The strings <code>public</code> or <code>private</code>, which
        respectively specify every package or no package. (This form requires
        the flag <code>--incompatible_package_group_has_public_syntax</code> to
        be set.)

        </ol>

        <p>In addition, the first two kinds of package specifications may also
        be prefixed with <code>-</code> to indicate that they are negated.</p>

        <p>The package group contains any package that matches at least one of
        its positive specifications and none of its negative specifications
        For instance, the value <code>[//foo/..., -//foo/tests/...]</code>
        includes all subpackages of <code>//foo</code> that are not also
        subpackages of <code>//foo/tests</code>. (<code>//foo</code> itself is
        included while </code>//foo/tests</code> itself is not.)</p>

        <p>Aside from public visibility, there is no way to directly specify
        packages outside the current repository.</p>

        <p>If this attribute is missing, it is the same as setting it to an
        empty list, which is also the same as setting it to a list containing
        only <code>private</code>.

        <p><i>Note:</i> Prior to Bazel 6.0, the specification <code>//...</code>
        had a legacy behavior of being the same as <code>public</code>. This
        behavior is fixed when
        <code>--incompatible_fix_package_group_reporoot_syntax</code> is
        enabled, which is the default after Bazel 6.0.</p>

        <p><i>Note:</i> Prior to Bazel 6.0, when this attribute is serialized as
        part of <code>bazel query --output=proto</code> (or
        <code>--output=xml</code>), the leading slashes are omitted. For
        instance, <code>//pkg/foo/...</code> will output as
        <code>\"pkg/foo/...\"</code>. This behavior is fixed when
        <code>--incompatible_package_group_includes_double_slash</code> is
        enabled, which is the default after Bazel 6.0.</p>
      </td>
    </tr>
    <tr>
      <td id="package_group.includes"><code>includes</code></td>
      <td>
        <p>List of <a href="/versions/8.3.0/concepts/labels">labels</a>; default is <code>[]</code></p>
        <p>Other package groups that are included in this one.</p>

        <p>The labels in this attribute must refer to other package groups.
        Packages in referenced package groups are taken to be part of this
        package group. This is transitive — if package group
        <code>a</code> includes package group <code>b</code>, and <code>b</code>
        includes package group <code>c</code>, then every package in
        <code>c</code> will also be a member of <code>a</code>.</p>

        <p>When used together with negated package specifications, note that the
        set of packages for each group is first computed independently and the
        results are then unioned together. This means that negated
        specifications in one group have no effect on the specifications in
        another group.</p>
      </td>
    </tr>
  </tbody>
</table>

<h3 id="package_group_example">Examples</h3>

<p>The following <code>package_group</code> declaration specifies a
package group called "tropical" that contains tropical fruits.</p>

<pre class="code">
package_group(
    name = "tropical",
    packages = [
        "//fruits/mango",
        "//fruits/orange",
        "//fruits/papaya/...",
    ],
)
</pre>

<p>The following declarations specify the package groups of a fictional
application:</p>

<pre class="code">
package_group(
    name = "fooapp",
    includes = [
        ":controller",
        ":model",
        ":view",
    ],
)

package_group(
    name = "model",
    packages = ["//fooapp/database"],
)

package_group(
    name = "view",
    packages = [
        "//fooapp/swingui",
        "//fooapp/webui",
    ],
)

package_group(
    name = "controller",
    packages = ["//fooapp/algorithm"],
)
</pre>

<!-- =================================================================
                        exports_files([label, ...])
     =================================================================
  -->

<h2 id="exports_files">exports_files</h2>

<pre>exports_files([<i>label</i>, ...], visibility, licenses)</pre>

<p>
  <code>exports_files()</code> specifies a list of files belonging to
  this package that are exported to other packages.
</p>

<p>
  The BUILD file for a package may only refer directly to source files belonging
  to another package if they are explicitly exported with an
  <code>exports_files()</code> statement. Read more about
  <a href="/versions/8.3.0/concepts/visibility#source-file-target-visibility">visibility of files</a>.
</p>
   <p>
  As a legacy behaviour, also files mentioned as input to a rule are exported
  with the default visibility until the flag
  <a href="https://github.com/bazelbuild/bazel/issues/10225"><code>--incompatible_no_implicit_file_export</code></a>
  is flipped. However, this behavior should not be relied upon and actively
  migrated away from.
</p>

<h3 id="exports_files_args">Arguments</h3>

<p>
  The argument is a list of names of files within the current package. A
  visibility declaration can also be specified; in this case, the files will be
  visible to the targets specified. If no visibility is specified, the files
  will be visible to every package, even if a package default visibility was
  specified in the <code><a href="functions.html#package">package</a></code>
  function. The <a href="common-definitions.html#common.licenses">licenses</a>
  can also be specified.
</p>

<h3 id="exports_files_example">Example</h3>

<p>
  The following example exports <code>golden.txt</code>, a
  text file from the <code>test_data</code> package, so that other
  packages may use it, for example, in the <code>data</code> attribute
  of tests.
</p>

<pre class="code">
# from //test_data/BUILD

exports_files(["golden.txt"])
</pre>

<!-- =================================================================
                               glob()
     =================================================================
  -->

<h2 id="glob">glob</h2>

<pre>glob(include, exclude=[], exclude_directories=1, allow_empty=True)</pre>

<p>
Glob is a helper function that finds all files that match certain path patterns,
and returns a new, mutable, sorted list of their paths. Glob only searches files
in its own package, and looks only for source files (not generated files nor
other targets).
</p>

<p>
A source file's Label is included in the result if the file's package-relative
path matches any of the <code>include</code> patterns and none of the
<code>exclude</code> patterns.
</p>

<p>
The <code>include</code> and <code>exclude</code> lists contain path patterns
that are relative to the current package. Every pattern may consist of one or
more path segments. As usual with Unix paths, these segments are separated by
<code>/</code>. The segments in the pattern are matched against the segments of
the path. Segments may contain the <code>*</code> wildcard: this matches
any substring in the path segment (even the empty substring), excluding the
directory separator <code>/</code>. This wildcard can be used multiple times
within one path segment. Additionally, the <code>**</code> wildcard can match
zero or more complete path segments, but it must be declared as a standalone
path segment.
</p>

Examples:
<ul>
<li><code>foo/bar.txt</code> matches exactly the <code>foo/bar.txt</code> file
in this package (unless <code>foo/</code> is a subpackage)</li>
<li><code>foo/*.txt</code> matches every file in the <code>foo/</code> directory
if the file ends with <code>.txt</code> (unless <code>foo/</code> is a
subpackage)</li>
<li><code>foo/a*.htm*</code> matches every file in the <code>foo/</code>
directory that starts with <code>a</code>, then has an arbitrary string (could
be empty), then has <code>.htm</code>, and ends with another arbitrary string
(unless <code>foo/</code> is a subpackage); such as <code>foo/axx.htm</code>
and <code>foo/a.html</code> or <code>foo/axxx.html</code></li>
<li><code>foo/*</code> matches every file in the <code>foo/</code> directory,
(unless <code>foo/</code> is a subpackage); it does not match <code>foo</code>
directory itself even if <code>exclude_directories</code> is set to
</code>0</code></li>
<li><code>foo/**</code> matches every file in every non-subpackage subdirectory
under package's first level subdirectory <code>foo/</code>; if
<code>exclude_directories</code> is set to </code>0</code>, <code>foo</code>
directory itself also matches the pattern; in this case, <code>**</code> is
considered to match zero path segments</li>
<li><code>**/a.txt</code> matches <code>a.txt</code> files in this package's
directory plus non-subpackage subdirectories.</li>
<li><code>**/bar/**/*.txt</code> matches every <code>.txt</code> file in every
non-subpackage subdirectory of this package, if at least one directory on the
resulting path is called <code>bar</code>, such as
<code>xxx/bar/yyy/zzz/a.txt</code> or <code>bar/a.txt</code> (remember that
<code>**</code> also matches zero segments) or <code>bar/zzz/a.txt</code></li>
<li><code>**</code> matches every file in every non-subpackage subdirectory of
this package</li>
<li><code>foo**/a.txt</code> is an invalid pattern, because <code>**</code> must
stand on its own as a segment</li>
<li><code>foo/</code> is an invalid pattern, because the second segment defined
after <code>/</code> is an empty string</li>
</ul>

<p>
If the <code>exclude_directories</code> argument is enabled (set to 1), files of
type directory will be omitted from the results (default 1).
</p>
<p>
If the <code>allow_empty</code> argument is set to <code>False</code>, the
<code>glob</code> function will error-out if the result would otherwise be the
empty list.
</p>
<p>
There are several important limitations and caveats:
</p>

<ol>
  <li>
    <p>
    Since <code>glob()</code> runs during BUILD file evaluation,
    <code>glob()</code> matches files only in your source tree, never
    generated files.  If you are building a target that requires both
    source and generated files, you must append an explicit list of generated
    files to the glob. See the <a href="#glob_example">example</a>
    below with <code>:mylib</code> and <code>:gen_java_srcs</code>.
    </p>
  </li>

  <li>
    <p>
      If a rule has the same name as a matched source file, the rule will
      "shadow" the file.
    </p>
    <p>
      To understand this, remember that <code>glob()</code> returns a list of
      paths, so using <code>glob()</code> in other rules' attribute (e.g.
      <code>srcs = glob(["*.cc"])</code>) has the same effect as listing the
      matched paths explicitly.  If for example <code>glob()</code> yields
      <code>["Foo.java", "bar/Baz.java"]</code> but there's also a rule in the
      package called "Foo.java" (which is allowed, though Bazel warns about it),
      then the consumer of the <code>glob()</code> will use the "Foo.java" rule
      (its outputs) instead of the "Foo.java" file. See
      <a href="https://github.com/bazelbuild/bazel/issues/10395#issuecomment-583714657">GitHub
      issue #10395</a> for more details.
    </p>
  </li>

  <li>
    Globs may match files in subdirectories.  And subdirectory names
    may be wildcarded.  However...
  </li>

  <li>
    <p>
    Labels are not allowed to cross the package boundary and glob does
    not match files in subpackages.
    </p>

    <p>
    For example, the glob expression <code>**/*.cc</code> in package
    <code>x</code> does not include <code>x/y/z.cc</code> if
    <code>x/y</code> exists as a package (either as
    <code>x/y/BUILD</code>, or somewhere else on the package-path). This
    means that the result of the glob expression actually depends on the
    existence of BUILD files &mdash; that is, the same glob expression would
    include <code>x/y/z.cc</code> if there was no package called
    <code>x/y</code> or it was marked as deleted using the
    <a href="/versions/8.3.0/docs/user-manual#flag--deleted_packages">--deleted_packages</a>
    flag.
    </p>

  </li>

  <li>
    The restriction above applies to all glob expressions,
    no matter which wildcards they use.
  </li>
  <li>
    A hidden file with filename starting with <code>.</code> is completely matched by
    both the <code>**</code> and the <code>*</code> wildcards. If you want to match a hidden file
    with a compound pattern, your pattern needs to begin with a <code>.</code>. For example,
    <code>*</code> and <code>.*.txt</code> will match <code>.foo.txt</code>, but <code>*.txt</code>
    will not.

    Hidden directories are also matched in the same manner. Hidden directories
    may include files that are not required as inputs, and can increase the
    number of unnecessarily globbed files and memory consumption. To exclude
    hidden directories, add them to the "exclude" list argument.
  </li>

  <li>
    The "**" wildcard has one corner case: the pattern
    <code>"**"</code> doesn't match the package's directory path. That is to
    say, <code>glob(["**"], exclude_directories = 0)</code> matches all files
    and directories transitively strictly under the current package's directory
    (but of course not going into directories of subpackages - see the previous
    note about that).
  </li>
</ol>

<p>
In general, you should <b>try to provide an appropriate extension (e.g. *.html)
instead of using a bare '*'</b> for a glob pattern. The more explicit name
is both self documenting and ensures that you don't accidentally match backup
files, or emacs/vi/... auto-save files.
</p>

<p>
When writing build rules you can enumerate the elements of the glob. This
enables generating individual rules for every input, for example. See the
<a href="#expanded_glob_example">expanded glob example</a> section below.
</p>

<h3 id="glob_example">Glob Examples</h3>

<p> Create a Java library built from all java files in this directory,
and all files generated by the <code>:gen_java_srcs</code> rule.</p>
<pre class="code">
java_library(
    name = "mylib",
    srcs = glob(["*.java"]) + [":gen_java_srcs"],
    deps = "...",
)

genrule(
    name = "gen_java_srcs",
    outs = [
        "Foo.java",
        "Bar.java",
    ],
    ...
)
</pre>

<p>Include all txt files in directory testdata except experimental.txt.
Note that files in subdirectories of testdata will not be included. If
you want those files to be included, use a recursive glob (**).</p>
<pre class="code">
sh_test(
    name = "mytest",
    srcs = ["mytest.sh"],
    data = glob(
        ["testdata/*.txt"],
        exclude = ["testdata/experimental.txt"],
    ),
)
</pre>

<h3 id="recursive_glob_example">Recursive Glob Examples</h3>


<p>Make the test depend on all txt files in the testdata directory and any
   of its subdirectories (and their subdirectories, and so on).
   Subdirectories containing a BUILD file are ignored. (See limitations
   and caveats above.)</p>
<pre class="code">
sh_test(
    name = "mytest",
    srcs = ["mytest.sh"],
    data = glob(["testdata/**/*.txt"]),
)
</pre>

<p>Create a library built from all java files in this directory and all
subdirectories except those whose path includes a directory named testing.
<b>This pattern should be avoided if possible, as it can reduce build
incrementality and therefore increase build times.</b>
</p>
<pre class="code">
java_library(
    name = "mylib",
    srcs = glob(
        ["**/*.java"],
        exclude = ["**/testing/**"],
    ),
)
</pre>

<h3 id="expanded_glob_example">Expanded Glob Examples</h3>

<p>
Create an individual genrule for *_test.cc in the current directory
that counts the number of lines in the file.
</p>

<pre class="code">
# Conveniently, the build language supports list comprehensions.
[genrule(
    name = "count_lines_" + f[:-3],  # strip ".cc"
    srcs = [f],
    outs = ["%s-linecount.txt" % f[:-3]],
    cmd = "wc -l $&lt; &gt;$@",
 ) for f in glob(["*_test.cc"])]
</pre>

<p>
If the BUILD file above is in package //foo and the package contains three
matching files, a_test.cc, b_test.cc and c_test.cc then running
<code>bazel query '//foo:all'</code> will list all rules that were generated:

<pre>
$ bazel query '//foo:all' | sort
//foo:count_lines_a_test
//foo:count_lines_b_test
//foo:count_lines_c_test
</pre>

<!-- =================================================================
                              select()
     =================================================================
-->

<h2 id="select">select</h2>

<pre>
select(
    {conditionA: valuesA, conditionB: valuesB, ...},
    no_match_error = "custom message"
)
</pre>

<p><code>select()</code> is the helper function that makes a rule attribute
  <a href="common-definitions.html#configurable-attributes">configurable</a>.
  It can replace the right-hand side of

  <i>almost</i>
  any attribute assignment so its value depends on command-line Bazel flags.
  You can use this, for example, to define platform-specific dependencies or to
  embed different resources depending on whether a rule is built in "developer"
  vs. "release" mode.
</p>

<p>Basic use is as follows:</p>

<pre class="code">
sh_binary(
    name = "mytarget",
    srcs = select({
        ":conditionA": ["mytarget_a.sh"],
        ":conditionB": ["mytarget_b.sh"],
        "//conditions:default": ["mytarget_default.sh"]
    })
)
</pre>

<p>This makes the <code>srcs</code> attribute of
  a <code>sh_binary</code> configurable by replacing its normal label
  list assignment with a <code>select</code> call that maps
  configuration conditions to matching values. Each condition is a label
  reference to
  a <code><a href="general.html#config_setting">config_setting</a></code> or
  <code><a href="platforms-and-toolchains.html#constraint_value">constraint_value</a></code>,
  which "matches" if the target's configuration matches an expected set of
  values. The value of <code>mytarget#srcs</code> then becomes whichever
  label list matches the current invocation.
</p>

<p>Notes:</p>

<ul>
  <li>Exactly one condition is selected on any invocation.
  </li>
  <li>If multiple conditions match and one is a specialization of the others,
    the specialization takes precedence. Condition B is considered a
    specialization of condition A if B has all the same flags and constraint
    values as A plus some additional flags or constraint values. This also
    means that specialization resolution is not designed to create an ordering as
    demonstrated in Example 2 below.
  </li>
  <li>If multiple conditions match and one is not a specialization of all the
    others, Bazel fails with an error, unless all conditions resolve to the same value.
  </li>
  <li>The special pseudo-label <code>//conditions:default</code> is
    considered to match if no other condition matches. If this condition
    is left out, some other rule must match to avoid an error.
  </li>
  <li><code>select</code> can be embedded <i>inside</i> a larger
    attribute assignment. So <code>srcs = ["common.sh"]
    + select({ ":conditionA": ["myrule_a.sh"], ...})</code> and <code>
    srcs = select({ ":conditionA": ["a.sh"]}) + select({ ":conditionB":
    ["b.sh"]})</code> are valid expressions.
  </li>
  <li><code>select</code> works with most, but not all, attributes. Incompatible
  attributes are marked <code>nonconfigurable</code> in their documentation.

<!-- =================================================================
                        subpackages()
     =================================================================
  -->

<h2 id="subpackages">subpackages</h2>

<pre>subpackages(include, exclude=[], allow_empty=True)</pre>

<p>
  <code>subpackages()</code> is a helper function, similar to <code>glob()</code>
  that lists subpackages instead of files and directories.  It uses the same
  path patterns as <code>glob()</code> and can match any subpackage that is a
  direct descendant of the currently loading BUILD file.  See <a
  href="#glob">glob</a> for a detailed explanation and examples of include and
  exclude patterns.
</p>

<p>
  The resulting list of subpackages returned is in sorted order and contains
  paths relative to the current loading package that match the given patterns in
  <code>include</code> and not those in <code>exclude</code>.

<h3 id=subpackages_example">Example</h3>

<p>
  The following example lists all the direct subpackages for the package <code>foo/BUILD</code>

<pre class="code">
# The following BUILD files exist:
# foo/BUILD
# foo/bar/baz/BUILD
# foo/bar/but/bad/BUILD
# foo/sub/BUILD
# foo/sub/deeper/BUILD
#
# In foo/BUILD a call to
subs1 = subpackages(include = ["**"])

# results in subs1 == ["sub", "bar/baz", "bar/but/bad"]
#
# 'sub/deeper' is not included because it is a subpackage of 'foo/sub' not of
# 'foo'

subs2 = subpackages(include = ["bar/*"])
# results in subs2 = ["bar/baz"]
#
# Since 'bar' is not a subpackage itself, this looks for any subpackages under
# all first level subdirectories of 'bar'.

subs3 = subpackages(include = ["bar/**"])
# results in subs3 = ["bar/baz", "bar/but/bad"]
#
# Since bar is not a subpackage itself, this looks for any subpackages which are
# (1) under all subdirectories of 'bar' which can be at any level, (2) not a
# subpackage of another subpackages.

subs4 = subpackages(include = ["sub"])
subs5 = subpackages(include = ["sub/*"])
subs6 = subpackages(include = ["sub/**"])
# results in subs4 and subs6 being ["sub"]
# results in subs5 = [].
#
# In subs4, expression "sub" checks whether 'foo/sub' is a package (i.e. is a
# subpackage of 'foo').
# In subs5, "sub/*" looks for subpackages under directory 'foo/sub'. Since
# 'foo/sub' is already a subpackage itself, the subdirectories will not be
# traversed anymore.
# In subs6, 'foo/sub' is a subpackage itself and matches pattern "sub/**", so it
# is returned. But the subdirectories of 'foo/sub' will not be traversed
# anymore.
</pre>

    <p>
    In general it is preferred that instead of calling this function directly
    that users use the 'subpackages' module of
    <a href="https://github.com/bazelbuild/bazel-skylib">skylib</a>.

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