This page covers how to get started using Bazel's query language to trace dependencies in your code.
For a language details and --output flag details, please see the
reference manuals, Bazel query reference
and Bazel cquery reference. You can get help by
typing bazel help query or bazel help cquery on the
command line.
To execute a query while ignoring errors such as missing targets, use the
--keep_going flag.
Finding the dependencies of a rule
To see the dependencies of //foo, use the
deps function in bazel query:
$ bazel query "deps(//foo)" //foo:foo //foo:foo-dep ...
This is the set of all targets required to build //foo.
Tracing the dependency chain between two packages
The library //third_party/zlib:zlibonly isn't in the BUILD file for
//foo, but it is an indirect dependency. How can
we trace this dependency path? There are two useful functions here:
allpaths and somepath. You may also want to exclude
tooling dependencies with --notool_deps if you care only about
what is included in the artifact you built, and not every possible job.
To visualize the graph of all dependencies, pipe the bazel query output through
the dot command-line tool:
$ bazel query "allpaths(//foo, third_party/...)" --notool_deps --output graph | dot -Tsvg > /tmp/deps.svg
When a dependency graph is big and complicated, it can be helpful start with a single path:
$ 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
If you do not specify --output graph with allpaths,
you will get a flattened list of the dependency graph.
$ 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
Aside: implicit dependencies
The BUILD file for //foo never references
//translations/tools:aggregator. So, where's the direct dependency?
Certain rules include implicit dependencies on additional libraries or tools.
For example, to build a genproto rule, you need first to build the Protocol
Compiler, so every genproto 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 --noimplicit_deps allows you to filter out
these deps from your query results. For cquery, this will include resolved toolchains.
Reverse dependencies
You might want to know the set of targets that depends on some target. For instance,
if you're going to change some code, you might want to know what other code
you're about to break. You can use rdeps(u, x) to find the reverse
dependencies of the targets in x within the transitive closure of u.
Bazel's Sky Query
supports the allrdeps function which allows you to query reverse dependencies
in a universe you specify.
Miscellaneous uses
You can use bazel query to analyze many dependency relationships.
What exists ...
What packages exist beneath foo?
bazel query 'foo/...' --output package
What rules are defined in the foo package?
bazel query 'kind(rule, foo:*)' --output label_kind
What files are generated by rules in the foo package?
bazel query 'kind("generated file", //foo:*)'
What targets are generated by starlark macro foo?
bazel query 'attr(generator_function, foo, //path/to/search/...)'
What's the set of BUILD files needed to build //foo?
bazel query 'buildfiles(deps(//foo))' | cut -f1 -d:
What are the individual tests that a test_suite expands to?
bazel query 'tests(//foo:smoke_tests)'
Which of those are C++ tests?
bazel query 'kind(cc_.*, tests(//foo:smoke_tests))'
Which of those are small? Medium? Large?
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))'
What are the tests beneath foo that match a pattern?
bazel query 'filter("pa?t", kind(".*_test rule", //foo/...))'
The pattern is a regex and is applied to the full name of the rule. It's similar to doing
bazel query 'kind(".*_test rule", //foo/...)' | grep -E 'pa?t'
What package contains file path/to/file/bar.java?
bazel query path/to/file/bar.java --output=package
What is the build label for path/to/file/bar.java?
bazel query path/to/file/bar.java
What rule target(s) contain file path/to/file/bar.java as a source?
fullname=$(bazel query path/to/file/bar.java)
bazel query "attr('srcs', $fullname, ${fullname//:*/}:*)"
What package dependencies exist ...
What packages does foo depend on? (What do I need to check out to build foo)
bazel query 'buildfiles(deps(//foo:foo))' --output package
What packages does the foo tree depend on, excluding foo/contrib?
bazel query 'deps(foo/... except foo/contrib/...)' --output package
What rule dependencies exist ...
What genproto rules does bar depend upon?
bazel query 'kind(genproto, deps(bar/...))'
Find the definition of some JNI (C++) library that is transitively depended upon by a Java binary rule in the servlet tree.
bazel query 'some(kind(cc_.*library, deps(kind(java_binary, //java/com/example/frontend/...))))' --output location
...Now find the definitions of all the Java binaries that depend on them
bazel query 'let jbs = kind(java_binary, //java/com/example/frontend/...) in
let cls = kind(cc_.*library, deps($jbs)) in
$jbs intersect allpaths($jbs, $cls)'
What file dependencies exist ...
What's the complete set of Java source files required to build foo?
Source files:
bazel query 'kind("source file", deps(//path/to/target/foo/...))' | grep java$
Generated files:
bazel query 'kind("generated file", deps(//path/to/target/foo/...))' | grep java$
What is the complete set of Java source files required to build QUX's tests?
Source files:
bazel query 'kind("source file", deps(kind(".*_test rule", javatests/com/example/qux/...)))' | grep java$
Generated files:
bazel query 'kind("generated file", deps(kind(".*_test rule", javatests/com/example/qux/...)))' | grep java$
What differences in dependencies between X and Y exist ...
What targets does //foo depend on that //foo:foolib does not?
bazel query 'deps(//foo) except deps(//foo:foolib)'
What C++ libraries do the foo tests depend on that the //foo production binary does not depend on?
bazel query 'kind("cc_library", deps(kind(".*test rule", foo/...)) except deps(//foo))'
Why does this dependency exist ...
Why does bar depend on groups2?
bazel query 'somepath(bar/...,groups2/...:*)'
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 bar. The query can then be further refined to:
Show me a path from docker/updater:updater_systest (a py_test) to some cc_library that it depends upon:
bazel query 'let cc = kind(cc_library, deps(docker/updater:updater_systest)) in somepath(docker/updater:updater_systest, $cc)'
Why does library //photos/frontend:lib depend on two variants of the same library //third_party/jpeglib and //third_party/jpeg?
This query boils down to: "show me the subgraph of //photos/frontend:lib that
depends on both libraries". When shown in topological order, the last element
of the result is the most likely culprit.
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
What depends on ...
What rules under bar depend on Y?
bazel query 'bar/... intersect allpaths(bar/..., Y)'
What targets directly depend on T, in T's package?
bazel query 'same_pkg_direct_rdeps(T)'
How do I break a dependency ...
What dependency paths do I have to break to make bar no longer depend on X?
To output the graph to a svg file:
bazel query 'allpaths(bar/...,X)' --output graph | dot -Tsvg > /tmp/dep.svg
Misc
How many sequential steps are there in the //foo-tests build?
Unfortunately, the query language can't currently give you the longest path
from x to y, but it can find the (or rather a) most distant node from the
starting point, or show you the lengths of the longest path from x to every
y that it depends on. Use maxrank:
bazel query 'deps(//foo-tests)' --output maxrank | tail -1 85 //third_party/zlib:zutil.c
The result indicates that there exist paths of length 85 that must occur in order in this build.