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+---
+layout: documentation
+title: Bazel Query How-To
+---
+<h1>Bazel query how-to</h1>
+
+<p>
+  This is a quick tutorial to get you started using Bazel's query language to
+  trace dependencies in your code.
+</p>
+
+<p>
+  For a language details and <code>--output</code> flag details, please see the reference
+  manuals, <a href="query.html">Bazel query reference</a> and <a href="cquery.html">Bazel cquery reference</a>.
+  You can get help by typing <code>bazel help query</code> or <code>bazel help cquery</code> on the command line.
+</p>
+
+<p>
+  To execute a query while ignoring errors such as missing targets, use the
+  <code>--keep_going</code> flag.
+</p>
+
+<h2>Contents</h2>
+
+<ul>
+<li><a href="#Finding_the_Dependencies_of_a_Ru">Finding the Dependencies of a Rule</a></li>
+<li><a href="#Tracing_the_Dependency_Chain_bet">Tracing the Dependency Chain between Two
+Packages</a>
+<ul><li><a href="#Aside_implicit_dependencies">Aside: implicit dependencies</a></li></ul></li>
+<li><a href="#Reverse_Dependencies">Reverse Dependencies</a></li>
+<li><a href="#Miscellaneous_Uses">Miscellaneous Uses</a>
+<ul><li><a href="#What_exists_">What exists ...</a>
+<ul><li><a href="#What_packages_exist_beneath_foo_">What packages exist beneath
+<code>foo</code>?</a></li>
+<li><a href="#What_rules_are_defined_in_the_foo">What rules are defined in the <code>foo</code>
+package?</a></li>
+<li><a href="#What_files_are_generated_by_rule">What files are generated by rules in the <code>foo</code>
+package?</a></li>
+<li><a href="#What_s_the_set_of_BUILD_files_ne">What's the set of BUILD files needed to build
+<code>//foo</code>?</a></li>
+<li><a href="#What_are_the_individual_tests_th">What are the individual tests that a <code>test_suite</code> expands
+to?</a>
+<ul><li><a href="#Which_of_those_are_C_tests_">Which of those are C++ tests?</a></li>
+<li><a href="#Which_of_those_are_small_Medium_">Which of those are small? Medium?
+Large?</a></li></ul></li>
+<li><a href="#What_are_the_tests_beneath_foo_t">What are the tests beneath <code>foo</code> that match a
+pattern?</a></li>
+<li><a href="#What_package_contains_file_java_">What package contains file
+<code>//path/to/file/bar.java</code>?
+</a></li>
+<li><a href="#What_is_the_build_label_for_java">What is the build label for
+<code>//path/to/file/bar.java</code>?
+</a></li>
+<li><a href="#What_build_rule_contains_file_ja">What build rule contains file
+<code>//path/to/file/bar.java</code> as a
+source?</a></li></ul></li>
+<li><a href="#What_package_dependencies_exist_">What package dependencies exist ...</a>
+<ul><li><a href="#What_packages_does_foo_depend_on">What packages does <code>foo</code> depend on? (What do I need to check out
+to build <code>foo</code>)</a></li>
+<li><a href="#What_packages_does_the_foo_">What packages does the <code>foo</code> tree depend on, excluding
+<code>foo/contrib</code>?</a></li></ul></li>
+<li><a href="#What_rule_dependencies_exist_">What rule dependencies exist ...</a>
+<ul><li><a href="#What_genproto_rules_does_bar_">What genproto rules does bar depend
+upon?</a></li>
+<li><a href="#Find_the_definition_of_some_JNI_">Find the definition of some JNI (C++) library that is transitively
+depended upon by a Java binary rule in the servlet
+tree.</a>
+<ul><li><a href="#_Now_find_the_definitions_of_all">...Now find the definitions of all the Java binaries that
+depend on them</a></li></ul></li></ul></li>
+<li><a href="#What_file_dependencies_exist_">What file dependencies exist ...</a>
+<ul><li><a href="#What_s_the_complete_set_of_Java_">What's the complete set of Java source files required to build
+QUX?</a></li>
+<li><a href="#What_is_the_complete_set_of_Java">What is the complete set of Java source files required to build
+QUX's tests?</a></li></ul></li>
+<li><a href="#What_differences_in_dependencies">What differences in dependencies between X and Y exist
+...</a>
+<ul><li><a href="#What_targets_does_foo_depend_on_">What targets does <code>//foo</code> depend on that <code>//foo:foolib</code> does
+not?</a></li>
+<li><a href="#What_C_libraries_do_the_foo_test">What C++ libraries do the <code>foo</code> tests depend on that the <code>//foo</code>
+production binary does <em>not</em> depend
+on?</a></li></ul></li>
+<li><a href="#Why_does_this_dependency_exist_">Why does this dependency exist ...</a>
+<ul><li><a href="#Why_does_bar_depend_on_groups">Why does <code>bar</code> depend on
+<code>groups2</code>?</a></li>
+<li><a href="#Show_me_a_path_from_docker_updater">Show me a path from <code>docker/updater:updater_systest</code> (a <code>py_test</code>)
+to some <code>cc_library</code> that it depends
+upon:</a></li>
+<li><a href="#Why_does_library_photos_frontend">Why does library <code>//photos/frontend:lib</code> depend on two variants of
+the same library <code>//third_party/jpeglib</code> and
+<code>//third_party/jpeg</code>?</a></li></ul></li>
+<li><a href="#What_depends_on_">What depends on ...</a>
+<ul><li><a href="#What_rules_under_bar_depend_o">What rules under bar depend on Y?</a></li>
+<li><a href="#What_are_the_intra_package_direct_rdeps">What targets directly depend on T, in T's
+package</a></li></ul></li>
+<li><a href="#How_do_I_break_a_dependency_">How do I break a dependency ...</a>
+<ul><li><a href="#What_dependency_paths_do_I_have_">What dependency paths do I have to break to make <code>bar</code> no longer
+depend on X?</a></li></ul></li>
+<li><a href="#Misc_">Misc ...</a>
+<ul><li><a href="#How_many_sequential_steps_are_th">How many sequential steps are there in the <code>ServletSmokeTests</code>
+build?</a></li></ul></li></ul></li>
+</ul>
+
+<p><a name="Finding_the_Dependencies_of_a_Ru"></a></p>
+
+<h2>Finding the Dependencies of a Rule</h2>
+
+<p>To see the dependencies of <code>//foo</code>, use the
+<code>deps</code> function in bazel query:</p>
+
+<pre>
+$ bazel query "deps(//foo)"
+//foo:foo
+//foo:foo-dep
+...
+</pre>
+
+<p>This is the set of all targets required to build <code>//foo</code>.</p>
+
+<p><a name="Tracing_the_Dependency_Chain_bet"></a></p>
+
+<h2>Tracing the Dependency Chain between Two Packages</h2>
+
+<p>The library <code>//third_party/zlib:zlibonly</code> isn't in the BUILD file for
+<code>//foo</code>, but it is an indirect dependency. How can
+we trace this dependency path?  There are two useful functions here:
+<code>allpaths</code> and <code>somepath</code></p>
+
+<pre>
+$ bazel query "somepath(//foo:foo, third_party/zlib:zlibonly)"
+//foo:foo
+//translations/tools:translator
+//translations/base:base
+//third_party/py/MySQL:MySQL
+//third_party/py/MySQL:_MySQL.so
+//third_party/mysql:mysql
+//third_party/zlib:zlibonly
+$ bazel query "allpaths(//foo, third_party/...)"
+  ...many errors detected in BUILD files...
+//foo:foo
+//translations/tools:translator
+//translations/tools:aggregator
+//translations/base:base
+//tools/pkg:pex
+//tools/pkg:pex_phase_one
+//tools/pkg:pex_lib
+//third_party/python:python_lib
+//translations/tools:messages
+//third_party/py/xml:xml
+//third_party/py/xml:utils/boolean.so
+//third_party/py/xml:parsers/sgmlop.so
+//third_party/py/xml:parsers/pyexpat.so
+//third_party/py/MySQL:MySQL
+//third_party/py/MySQL:_MySQL.so
+//third_party/mysql:mysql
+//third_party/openssl:openssl
+//third_party/zlib:zlibonly
+//third_party/zlib:zlibonly_v1_2_3
+//third_party/python:headers
+//third_party/openssl:crypto
+</pre>
+
+<p><a name="Aside_implicit_dependencies"></a></p>
+
+<h3>Aside: implicit dependencies</h3>
+
+<p>The BUILD file for <code>//foo</code> never references
+<code>//translations/tools:aggregator</code>. So, where's the direct dependency?</p>
+
+<p>Certain rules include implicit dependencies on additional libraries or tools.
+For example, to build a <code>genproto</code> rule, you need first to build the Protocol
+Compiler, so every <code>genproto</code> rule carries an implicit dependency on the
+protocol compiler.  These dependencies are not mentioned in the build file,
+but added in by the build tool.  The full set of implicit dependencies is
+  currently undocumented. Using <code>--noimplicit_deps</code> allows you to filter out
+  these deps from your query results.
+
+<p><a name="Reverse_Dependencies"></a></p>
+
+<h2>Reverse Dependencies</h2>
+
+<p>You might want to know the set of targets that depends on some target.  e.g.,
+if you're going to change some code, you might want to know what other code
+you're about to break.  You can use <code>rdeps(u, x)</code> to find the reverse
+dependencies of the targets in <code>x</code> within the transitive closure of <code>u</code>.</p>
+
+Bazel's <a href="https://docs.bazel.build/versions/master/query.html#sky-query">Sky Query</a> allows
+supports the <code>allrdeps</code> function which allows you to query rdeps in the entire
+universe of the build.
+<p><a name="Miscellaneous_Uses"></a></p>
+
+<h2>Miscellaneous Uses</h2>
+
+<p>You can use <code>bazel query</code> to analyze many dependency relationships.</p>
+
+<p><a name="What_exists_"></a></p>
+
+<h3>What exists ...</h3>
+
+<p><a name="What_packages_exist_beneath_foo_"></a></p>
+
+<h4>What packages exist beneath <code>foo</code>?</h4>
+
+<pre>bazel query 'foo/...' --output package</pre>
+
+<p><a name="What_rules_are_defined_in_the_gw"></a></p>
+
+<h4>What rules are defined in the <code>foo</code> package?</h4>
+
+<pre>bazel query 'kind(rule, foo:all)' --output label_kind</pre>
+
+<p><a name="What_files_are_generated_by_rule"></a></p>
+
+<h4>What files are generated by rules in the <code>foo</code> package?</h4>
+
+<pre>bazel query 'kind("generated file", //foo:*)'</pre>
+
+<p><a name="What_s_the_set_of_BUILD_files_ne"></a></p>
+
+<h4>What's the set of BUILD files needed to build <code>//foo</code>?</h4>
+
+<pre>bazel query 'buildfiles(deps(//foo))' --output location | cut -f1 -d:</pre>
+
+<p><a name="What_are_the_individual_tests_th"></a></p>
+
+<h4>What are the individual tests that a <code>test_suite</code> expands to?</h4>
+
+<pre>bazel query 'tests(//foo:smoke_tests)'</pre>
+
+<p><a name="Which_of_those_are_C_tests_"></a></p>
+
+<h4>Which of those are C++ tests?</h4>
+
+<pre>bazel query 'kind(cc_.*, tests(//foo:smoke_tests))'</pre>
+
+<p><a name="Which_of_those_are_small_Medium_"></a></p>
+
+<h4>Which of those are small?  Medium?  Large?</h4>
+
+<pre>
+bazel query 'attr(size, small, tests(//foo:smoke_tests))'
+
+bazel query 'attr(size, medium, tests(//foo:smoke_tests))'
+
+bazel query 'attr(size, large, tests(//foo:smoke_tests))'
+</pre>
+
+<p><a name="What_are_the_tests_beneath_foo_t"></a></p>
+
+<h4>What are the tests beneath <code>foo</code> that match a pattern?</h4>
+
+<pre>bazel query 'filter("pa?t", kind(".*_test rule", //foo/...))'</pre>
+
+<p>The pattern is a regex and is applied to the full name of the rule. It's similar to doing</p>
+
+<pre>bazel query 'kind(".*_test rule", //foo/...)' | grep -E 'pa?t'</pre>
+
+<p><a name="What_package_contains_file_java_"></a></p>
+
+<h4>What package contains file //path/to/file/bar.java`?</h4>
+
+<pre> bazel query 'buildfiles(//path/to/file/bar.java)' --output=package</pre>
+
+<p><a name="What_is_the_build_label_for_java"></a></p>
+
+<h4>What is the build label for //path/to/file/bar.java?</h4>
+
+<pre>bazel query //path/to/file/bar.java</pre>
+
+<p><a name="What_build_rule_contains_file_ja"></a></p>
+
+<h4>What rule target(s) contain file <code>//path/to/file/bar.java</code> as a source?</h4>
+
+<pre>
+fullname=$(bazel query //path/to/file/bar.java)
+bazel query "attr('srcs', $fullname, ${fullname//:*/}:*)"
+</pre>
+
+<p><a name="What_package_dependencies_exist_"></a></p>
+
+<h3>What package dependencies exist ...</h3>
+
+<p><a name="What_packages_does_foo_depend_on"></a></p>
+
+<h4>What packages does <code>foo</code> depend on? (What do I need to check out to build <code>foo</code>)</h4>
+
+<pre>bazel query 'buildfiles(deps(//foo:foo))' --output package</pre>
+
+<p>Note, <code>buildfiles</code> is required in order to correctly obtain all files
+referenced by <code>subinclude</code>; see the reference manual for details.</p>
+
+<p><a name="What_packages_does_the_foo_"></a></p>
+
+<h4>What packages does the <code>foo</code> tree depend on, excluding <code>foo/contrib</code>?</h4>
+
+<pre>bazel query 'deps(foo/... except foo/contrib/...)' --output package</pre>
+
+<p><a name="What_rule_dependencies_exist_"></a></p>
+
+<h3>What rule dependencies exist ...</h3>
+
+<p><a name="What_genproto_rules_does_bar_"></a></p>
+
+<h4>What genproto rules does bar depend upon?</h4>
+
+<pre>bazel query 'kind(genproto, deps(bar/...))'</pre>
+
+<p><a name="Find_the_definition_of_some_JNI_"></a></p>
+
+<h4>Find the definition of some JNI (C++) library that is transitively depended upon by a Java binary rule in the servlet tree.</h4>
+
+<pre>bazel query 'some(kind(cc_.*library, deps(kind(java_binary, //java/com/example/frontend/...))))' --output location</pre>
+<p><a name="_Now_find_the_definitions_of_all"></a></p>
+
+<h5>...Now find the definitions of all the Java binaries that depend on them</h5>
+
+<pre>bazel query 'let jbs = kind(java_binary, //java/com/example/frontend/...) in
+  let cls = kind(cc_.*library, deps($jbs)) in
+    $jbs intersect allpaths($jbs, $cls)'
+</pre>
+
+<p><a name="What_file_dependencies_exist_"></a></p>
+
+<h3>What file dependencies exist ...</h3>
+
+<p><a name="What_s_the_complete_set_of_Java_"></a></p>
+
+<h4>What's the complete set of Java source files required to build foo?</h4>
+
+<p>Source files:</p>
+
+<pre>bazel query 'kind("source file", deps(//path/to/target/foo/...))' | grep java$</pre>
+
+<p>Generated files:</p>
+
+<pre>bazel query 'kind("generated file", deps(//path/to/target/foo/...))' | grep java$</pre>
+
+<p><a name="What_is_the_complete_set_of_Java"></a></p>
+
+<h4>What is the complete set of Java source files required to build QUX's tests?</h4>
+
+<p>Source files:</p>
+
+<pre>bazel query 'kind("source file", deps(kind(".*_test rule", javatests/com/example/qux/...)))' | grep java$</pre>
+
+<p>Generated files:</p>
+
+<pre>bazel query 'kind("generated file", deps(kind(".*_test rule", javatests/com/example/qux/...)))' | grep java$</pre>
+
+<p><a name="What_differences_in_dependencies"></a></p>
+
+<h3>What differences in dependencies between X and Y exist ...</h3>
+
+<p><a name="What_targets_does_foo_depend_on_"></a></p>
+
+<h4>What targets does <code>//foo</code> depend on that <code>//foo:foolib</code> does not?</h4>
+
+<pre>bazel query 'deps(//foo) except deps(//foo:foolib)'</pre>
+
+<p><a name="What_C_libraries_do_the_foo_test"></a></p>
+
+<h4>What C++ libraries do the <code>foo</code> tests depend on that the <code>//foo</code> production binary does <em>not</em> depend on?</h4>
+
+<pre>bazel query 'kind("cc_library", deps(kind(".*test rule", foo/...)) except deps(//foo))'</pre>
+
+<p><a name="Why_does_this_dependency_exist_"></a></p>
+
+<h3>Why does this dependency exist ...</h3>
+
+<p><a name="Why_does_bar_depend_on_groups"></a></p>
+
+<h4>Why does <code>bar</code> depend on <code>groups2</code>?</h4>
+
+<pre>bazel query 'somepath(bar/...,groups2/...:*)'</pre>
+
+<p>Once you have the results of this query, you will often find that a single
+target stands out as being an unexpected or egregious and undesirable
+dependency of <code>bar</code>.  The query can then be further refined to:</p>
+
+<p><a name="Show_me_a_path_from_docker_updater"></a></p>
+
+<h4>Show me a path from <code>docker/updater:updater_systest</code> (a <code>py_test</code>) to some <code>cc_library</code> that it depends upon:</h4>
+
+<pre>bazel query 'let cc = kind(cc_library, deps(docker/updater:updater_systest)) in
+  somepath(docker/updater:updater_systest, $cc)'</pre>
+
+<p><a name="Why_does_library_photos_frontend"></a></p>
+
+<h4>Why does library <code>//photos/frontend:lib</code> depend on two variants of the same library <code>//third_party/jpeglib</code> and <code>//third_party/jpeg</code>?</h4>
+
+<p>This query boils down to: "show me the subgraph of <code>//photos/frontend:lib</code> that
+depends on both libraries".  When shown in topological order, the last element
+of the result is the most likely culprit.</p>
+
+<pre>bazel query 'allpaths(//photos/frontend:lib, //third_party/jpeglib)
+                intersect
+               allpaths(//photos/frontend:lib, //third_party/jpeg)'
+//photos/frontend:lib
+//photos/frontend:lib_impl
+//photos/frontend:lib_dispatcher
+//photos/frontend:icons
+//photos/frontend/modules/gadgets:gadget_icon
+//photos/thumbnailer:thumbnail_lib
+//third_party/jpeg/img:renderer
+</pre>
+
+<p><a name="What_depends_on_"></a></p>
+
+<h3>What depends on  ...</h3>
+
+<p><a name="What_rules_under_bar_depend_o"></a></p>
+
+<h4>What rules under bar depend on Y?</h4>
+
+<pre>bazel query 'bar/... intersect allpaths(bar/..., Y)'</pre>
+
+<p>Note: <code>X intersect allpaths(X, Y)</code> is the general idiom for the query "which X
+depend on Y?" If expression X is non-trivial, it may be convenient to bind a
+name to it using <code>let</code> to avoid duplication.</p>
+
+<p><a name="What_are_the_intra_package_direct_rdeps"></a></p>
+
+<h4>What targets directly depend on T, in T's package?</h4>
+
+<pre>bazel query 'let t = T in rdeps(siblings($t), $t, 1)'</pre>
+
+<p><a name="How_do_I_break_a_dependency_"></a></p>
+
+<h3>How do I break a dependency ...</h3>
+
+<p><!-- TODO find a convincing value of X to plug in here -->
+<a name="What_dependency_paths_do_I_have_"></a></p>
+
+<h4>What dependency paths do I have to break to make <code>bar</code> no longer depend on X?</h4>
+
+<p>To output the graph to a <code>png</code> file:</p>
+
+<pre>bazel query 'allpaths(bar/...,X)' --output graph | dot -Tpng &gt; /tmp/dep.png</pre>
+
+<p><a name="Misc_"></a></p>
+
+<h3>Misc ...</h3>
+
+<p><a name="How_many_sequential_steps_are_th"></a></p>
+
+<h4>How many sequential steps are there in the <code>//foo-tests</code> build?</h4>
+
+<p>Unfortunately, the query language can't currently give you the longest path
+from x to y, but it can find the (or rather <em>a</em>) most distant node from the
+starting point, or show you the <em>lengths</em> of the longest path from x to every
+y that it depends on.  Use <code>maxrank</code>:</p>
+
+<pre>bazel query 'deps(//foo-tests)' --output maxrank | tail -1
+85 //third_party/zlib:zutil.c</pre>
+
+<p>The result indicates that there exist paths of length 85 that must occur in
+order in this build.</p>