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Buck2 Cheat Sheet

This section provides example command lines that you can use to obtain information about Buck2 and about your build. These techniques can help you to understand how your build works and to troubleshoot issues with your build. These examples use the buck2 cquery command. We recommend cquery over uquery in most cases because cquery operates on the configured graph, which means that targets have had the expected configurations applied on them.

  • How do I find all the targets for a package?
  • How do I specify more than one target to buck2 cquery?
  • How do I get the attribute names and values for the targets that result from a query?
  • How do I perform a query inside of a rule?
  • How do I find the dependencies for a target, that is, the targets on which a specified target depends?
  • How do I find the reverse-dependencies for a target, that is, the targets that depend on a specified target?
  • How do I find the build file that contains the target that owns a source file?

How do I find all the targets for a package?

Specify a build target pattern that represents the targets in the package.

buck2 cquery //path/to/dir/...

The buck2 cquery command can accept a build target pattern as a parameter. If you specify a build target pattern, Buck2 evaluates this pattern and shows all the build targets that match it.

How do I specify more than one target to buck2 cquery?

Use the buck2 cquery set() operator. The following command line returns the target main in the build file in the root of the Buck2 project and all the targets from the build file in the myclass subdirectory of the root.

buck2 cquery "set( '//:main' '//myclass:' )"

How do I get the attribute names and values for the targets returned by a query?

Add the --output-attribute <ATTRIBUTE> or --output-all-attributes option to the command line, followed by regular expressions that represent the attributes of interest.

buck2 cquery "deps(//foo:bar)" --output-attribute 'name' 'exported_headers'

The --output-attribute option enables you to specify which attributes Buck2 should return. Instead of returning the names of the targets that match the query expression, Buck2 returns the names and values of the specified attributes for those targets in JSON format. Attributes are specified as regular expressions. For example, '.*' matches all attributes. See the buck2 cquery docs for more details. The output for the example query above might look something like the following.

{"//foo/bar/lib:lib" : {"exported_headers" : [ "App/util.h" ],"name" : "lib"},"//foo/bar:app" : {"exported_headers" : [ "App/lib.h" ],"name" : "app"}}

How do I perform a query** *inside* **of a rule?

Buck2 supports certain string parameter macros to be used when defining a target. You can use the query macros as such:

$(query_targets "queryfunction(//:foo)")
$(query_outputs "queryfunction(//:foo)")
$(query_targets_and_outputs [SEPARATOR] "queryfunction(//:foo)")

Note, however, that the query macros are supported only for genrule and apk_genrule.

How do I find the dependencies for a target?

Use the deps() operator.

buck2 cquery "deps('//foo:bar')"
buck2 cquery "deps('//foo:bar', 1, first_order_deps())"
buck2 cquery "deps(set('//foo:bar' '//foo:lib' '//foo/baz:util'))"

The deps operator finds the dependencies of the specified targets. The first argument represents the targets of interest. This can be a single build target or build target pattern, or a set of these. The optional second argument is the depth of the search for dependencies from the specified targets. For example, 1, as shown in the example above, returns only the direct dependencies. If you do not provide this argument, the output is the complete set of transitive dependencies. How do I find the reverse-dependencies for a target, that is, the targets that** *depend on* **a specified target? Use the buck2 cquery rdeps() (reverse dependencies) operator. The following example, returns the targets in the transitive closure of //foo:bar that depend directly on //example:baz.

buck2 cquery "rdeps('//foo:bar', '//example:baz', 1)"

How do I find the buildfile that contains the target that owns a source file?

In order to find the build file associated with a source file, combine the owner operator with buildfile. For example,

buck2 cquery "buildfile(owner('foo/bar/main.cpp'))"

first finds the targets that own foo/bar/main.cpp and then returns the build files, such as foo/bar/BUCK, that define those targets.