src/main/java/com/google/devtools/build/docgen/templates/be/functions.vm

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title: Functions
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<h1>Functions</h1>

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<div class="toc">
  <h1>Contents</h1>
  <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>
  </ul>
</div>
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<!-- =================================================================
                              package()
     =================================================================
-->

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

<pre>
package(default_deprecation, default_testonly, default_visibility, features)
</pre>
<p>This function declares metadata that applies to every subsequent rule in the
package. It is used at most once within a package (BUILD file).</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_visibility"><code>default_visibility</code></td>
      <td>
        <p><code>List of <a href="../build-ref.html#labels">labels</a>; optional</code></p>
        <p>The default visibility of the rules in this package.</p>
        <p>Every rule in this package has the visibility specified in this
        attribute, unless otherwise specified in the <code>visibility</code>
        attribute of the rule. For detailed information about the syntax of this
        attribute, see the documentation of the
        <a href="common-definitions.html#common.visibility">visibility</a>
        attribute. 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><code>String; optional</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_testonly"><code>default_testonly</code></td>
      <td>
        <p><code>Boolean; optional; default is 0 except as noted</code></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 1.</p>
      </td>
    </tr>
    <tr>
      <td id="package.features"><code>features</code></td>
      <td>
        <p><code>List strings; optional</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 packages and assigns a label to the
group. The label can be referenced in <code>visibility</code> attributes.</p>

<p>Package groups are used for visibility control.  You can grant access to a rule
to one or more package groups, every rule in the entire source tree, or only to rules declared
in the same package. For more detailed description of the visibility system, see
the <a href="common-definitions.html#common.visibility">visibility</a> attribute.

<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><code><a href="../build-ref.html#name">Name</a>; required</code></p>
        <p>A unique name for this target.</p>
      </td>
    </tr>
    <tr>
      <td id="package_group.packages"><code>packages</code></td>
      <td>
        <p><code>List of <a href="../build-ref.html#packages">Package</a>; optional</code></p>
        <p>A complete enumeration of packages in this group.</p>

        <p>Packages should be referred to using their full names,
        starting with a double slash. For
        example, <code>//foo/bar/main</code> is a valid element
        of this list.</p>

        <p>You can also specify wildcards: the specification
        <code>//foo/...</code> specifies every package under
        <code>//foo</code>, including <code>//foo</code> itself.</p>

        <p>Package specifications can be prefixed with <code>-</code> to
        indicate negation: the specification <code>-//foo/bar/...</code>
        excludes all packages under <code>//foo/bar</code> that would
        otherwise have been matched by the package patterns in the
        current <code>package_group</code>. When used together with
        <code>includes</code>, the set of packages for each package group
        is computed and then the results are unioned: negative patterns
        in one package group do not affect the result of included package
        groups.

        <p>If this attribute is missing, the package group itself will contain
        no packages (but it can still include other package groups).</p>
      </td>
    </tr>
    <tr>
      <td id="package_group.includes"><code>includes</code></td>
      <td>
        <p><code>List of <a href="../build-ref.html#labels">labels</a>; optional</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, that is, if package
        group <code>a</code> contains package group <code>b</code>,
        and <code>b</code> contains package group <code>c</code>, every
        package in <code>c</code> will also be a member of <code>a</code>.</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
  <pre>exports_files()</pre> statement.
  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 can be used anywhere a list of filenames
is expected.  It takes one or two lists of filename patterns containing
the <code>*</code> wildcard: as per the Unix shell, this wildcard
matches any string excluding the directory separator <code>/</code>.
In addition filename patterns can contain the recursive <code>**</code>
wildcard. This wildcard will match zero or more complete
path segments separated by the directory separator <code>/</code>.
This wildcard can only be used as a complete path segment. For example,
<code>"x/**/*.java"</code> is valid, but <code>"test**/testdata.xml"</code>
and <code>"**.java"</code> are both invalid. No other wildcards are supported.
</p>
<p>
Glob returns a sorted list of every file in the current package that:
</p>
<ul>
  <li>Matches at least one pattern in <code>include</code>. </li>
  <li>Does not match any of the patterns in <code>exclude</code> (default []).</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>
    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, create a list of generated
    files. This list can be specified by using the labels for the generated
    files or using the label
    for the target that produces the generated files.
    Use <code>+</code> to add the list of
    generated files to the result of the <code>glob()</code> call as shown in
    the <a href="#glob_example">example</a>
    below with the target <code>:gen_java_srcs</code>.
  </li>

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

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

    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="../user-manual.html#flag--deleted_packages">--deleted_packages</a>
    flag.

  </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.
  </li>
  <li>
    If a rule and a source file with the same name both exist in the package, the glob will
    return the outputs of the rule instead of the source file.
  </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.
  This can be used, 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 usage is as follows:</p>

<pre class="code">
sh_binary(
    name = "myrule",
    srcs = select({
        ":conditionA": ["myrule_a.sh"],
        ":conditionB": ["myrule_b.sh"],
        "//conditions:default": ["myrule_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> instance,
  which "matches" if the rule's configuration matches an expected set of
  values. The value of <code>myrule#srcs</code> then becomes whichever
  label list matches the current invocation.
</p>

<p>Further 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 as A plus some
    additional flags. However, the number of constraint values that A and B have
    are not considered in this comparison -- one condition cannot match a
    platform <i>more than</i> another condition does.
  </li>
  <li>If multiple conditions match and one is not a specialization of all the
    others, Bazel fails with an error.
  </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.

  </li>
</ul>

By default, Bazel produces the following error when no conditions match:
<pre class="code">
Configurable attribute "foo" doesn't match this configuration (would a default
condition help?).
Conditions checked:
 //pkg:conditionA.
 //pkg:conditionB.
</pre>

<code>no_match_error</code> can be used to signal more precise errors.

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

<pre class="code">
config_setting(
    name = "windows",
    values = {
        "crosstool_top": "//crosstools/windows",
    },
)

cc_binary(
    name = "multiplatform_app",
    ...
    linkopts = select({
        ":windows": [
            "-Wl,windows_support1.lib",
            "-Wl,windows_support2.lib",
        ],
        "//conditions:default": [],
    ...
)
</pre>

<p>In the above example, <code>multiplatform_app</code> links with additional
  options when invoked with <code>bazel build //pkg:multiplatform_app
  --crosstool_top=//crosstools/windows </code>.

<p>

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