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BUILD.bazel add -version flag to both buildozer and unused_deps (#439) Nov 20, 2018 Add dictionary handling (#421) Nov 15, 2018
main.go add -version flag to both buildozer and unused_deps (#439) Nov 20, 2018


Buildozer is a command line tool to rewrite multiple Bazel BUILD files using standard commands.


  1. Build a binary and put it into your $GOPATH/bin:
go get


buildozer [OPTIONS] ['command args' | -f FILE ] label-list

Here, label-list is a comma-separated list of Bazel labels, for example //path/to/pkg1:rule1, //path/to/pkg2:rule2. Buildozer reads commands from FILE (- for stdin (format: |-separated command line arguments to buildozer, excluding flags))

You should specify at least one command and one target. Buildozer will execute all commands on all targets. Commands are executed in order, files are processed in parallel.


Targets look like Bazel labels, but there can be some differences in presence of macros.

  • Use the label notation to refer to a rule: //buildtools/buildozer:edit
  • Use the __pkg__ suffix to refer to the package declaration: //buildtools/buildozer:__pkg__
  • Use an asterisk to refer to all rules in a file: //pkg:*
  • Use ... to refer to all descendant BUILD files in a directory: //pkg/...:*
  • Use percent to refer to all rules of a certain kind: //pkg:%java_library
  • Use percent-and-number to refer to a rule that begins at a certain line: //pkg:%123.
  • Use - for the package name if you want to process standard input stream instead of a file: -:all_tests.


OPTIONS include the following options:

  • -stdout : write changed BUILD file to stdout
  • -buildifier : format output using a specific buildifier binary. If empty, use built-in formatter.
  • -k : apply all commands, even if there are failures
  • -quiet : suppress informational messages
  • -shorten_labels : convert added labels to short form, e.g. //foo:bar => :bar
  • -types: Filter the targets, keeping only those of the given types, e.g. buildozer -types go_library,go_binary 'print rule' '//buildtools/buildozer:*'
  • -eol-comments=false: When adding new comments, put them on a separate line.

See buildozer -help for the full list.

Edit commands

Buildozer supports the following commands('command args'):

  • add <attr> <value(s)>: Adds value(s) to a list attribute of a rule. If a value is already present in the list, it is not added.
  • new_load <path> <[to=]from(s)>: Add a load statement for the given path, importing the symbols. Before using this, make sure to run buildozer 'fix movePackageToTop'. Afterwards, consider running buildozer 'fix unusedLoads'.
  • comment <attr>? <value>? <comment>: Add a comment to a rule, an attribute, or a specific value in a list. Spaces in the comment should be escaped with backslashes.
  • print_comment <attr>? <value>?
  • delete: Delete a rule.
  • fix <fix(es)>?: Apply a fix.
  • move <old_attr> <new_attr> <value(s)>: Moves value(s) from the list old_attr to the list new_attr. The wildcard * matches all values.
  • new <rule_kind> <rule_name> [(before|after) <relative_rule_name>]: Add a new rule at the end of the BUILD file (before/after <relative_rule>).
  • print <attr(s)>
  • remove <attr>: Removes attribute attr.
  • remove <attr> <value(s)>: Removes value(s) from the list attr. The wildcard * matches all attributes. Lists containing none of the value(s) are not modified.
  • rename <old_attr> <new_attr>: Rename the old_attr to new_attr which must not yet exist.
  • replace <attr> <old_value> <new_value>: Replaces old_value with new_value in the list attr. Wildcard * matches all attributes. Lists not containing old_value are not modified.
  • substitute <attr> <old_regexp> <new_template>: Replaces strings which match old_regexp in the list attr according to new_template. Wildcard * matches all attributes. The regular expression must follow RE2 syntax. new_template may be a simple replacement string, but it may also expand numbered or named groups using $0 or $x. Lists without strings that match old_regexp are not modified.
  • set <attr> <value(s)>: Sets the value of an attribute. If the attribute was already present, its old value is replaced.
  • set_if_absent <attr> <value(s)>: Sets the value of an attribute. If the attribute was already present, no action is taken.
  • set kind <value>: Set the target type to value.
  • copy <attr> <from_rule>: Copies the value of attr between rules. If it exists in the to_rule, it will be overwritten.
  • copy_no_overwrite <attr> <from_rule>: Copies the value of attr between rules. If it exists in the to_rule, no action is taken.
  • dict_add <attr> <(key:value)(s)>: Sets the value of a key for the dict attribute attr. If the key was already present, it will not be overwritten
  • dict_set <attr> <(key:value)(s)>: Sets the value of a key for the dict attribute attr. If the key was already present, its old value is replaced.
  • dict_delete <attr> <key(s)>: Deletes the key for the dict attribute attr.

Here, <attr> represents an attribute (being added/renamed/deleted etc.), e.g.: srcs, <value(s)> represents values of the attribute and so on. A '?' indicates that the preceding argument is optional.

The fix command without a fix specified applied to all eligible fixes. Use //path/to/pkg:__pkg__ as label for file level changes like new_load and new_rule. A transformation can be applied to all rules of a particular kind by using %rule_kind at the end of the label(see examples below).


# Edit //pkg:rule and //pkg:rule2, and add a dependency on //base
buildozer 'add deps //base' //pkg:rule //pkg:rule2

# A load for a skylark file in //pkg
buildozer 'new_load /tools/build_rules/build_test build_test' //pkg:__pkg__

# Change the default_visibility to public for the package //pkg
buildozer 'set default_visibility //visibility:public' //pkg:__pkg__

# Change all gwt_module targets to java_library in the package //pkg
buildozer 'set kind java_library' //pkg:%gwt_module

# Replace the dependency on pkg_v1 with a dependency on pkg_v2
buildozer 'replace deps //pkg_v1 //pkg_v2' //pkg:rule

# Replace all dependencies using regular expressions.
buildozer 'substitute deps //old/(.*) //new/${1}' //pkg:rule

# Delete the dependency on foo in every cc_library in the package
buildozer 'remove deps foo' //pkg:%cc_library

# Delete the testonly attribute in every rule in the package
buildozer 'remove testonly' '//pkg:*'

# Add a comment to the timeout attribute of //pkg:rule_test
buildozer 'comment timeout Delete\ this\ after\ 2015-12-31.' //pkg:rule_test

# Add a new rule at the end of the file
buildozer 'new java_library foo' //pkg:__pkg__

# Add a cc_binary rule named new_bin before the rule named tests
buildozer 'new cc_binary new_bin before tests' //:__pkg__

# Copy an attribute from `protolib` to `py_protolib`.
buildozer 'copy testonly protolib' //pkg:py_protolib

# Set two attributes in the same rule
buildozer 'set compile 1' 'set srcmap 1' //pkg:rule

# Make a default explicit in all soy_js rules in a package
buildozer 'set_if_absent allowv1syntax 1' //pkg:%soy_js

# Add an attribute new_attr with value "def_val" to all cc_binary rules
# Note that special characters will automatically be escaped in the string
buildozer 'add new_attr def_val' //:%cc_binary

Print commands

They work just like the edit commands. Expect a return code of 3 as they are not modifying any file.

  • print <attribute(s)>: For each target, prints the value of the attributes (see below).
  • print_comment <attr>? <value>?: Prints a comment associated with a rule, an attribute or a specific value in a list.

The print command prints the value of the attributes. If a target doesn't have the attribute, a warning is printed on stderr.

There are some special attributes in the print command:

  • kind: displays the name of the function
  • label: the fully qualified label
  • rule: the entire rule definition
  • startline: the line number on which the rule begins in the BUILD file
  • endline: the line number on which the rule ends in the BUILD file


# Print the kind of a target
buildozer 'print kind' base  # output: cc_library

# Print the name of all cc_library in //base
buildozer 'print name' base:%cc_library

# Get the default visibility of the //base package
buildozer 'print default_visibility' base:%package

# Print labels of cc_library targets in //base that have a deps attribute
buildozer 'print label deps' base:%cc_library 2>/dev/null | cut -d' ' -f1

# Print the list of labels in //base that explicitly set the testonly attribute:
buildozer 'print label testonly' 'base:*' 2>/dev/null

# Print the entire definition (including comments) of the //base:heapcheck rule:
buildozer 'print rule' //base:heapcheck

Converting labels

Buildozer works at the syntax-level. It doesn't evaluate the BUILD files. If you need to query the information Bazel has, please use bazel query. If you have a list of Bazel labels, chances are that some of them are generated by BUILD extensions. Labels in Buildozer are slightly different from labels in Bazel. Bazel cares about the generated code, while Buildozer looks at the BUILD file before macro expansion.

To see the expanded BUILD files, try:

bazel query --output=build //path/to/BUILD

Do multiple changes at once

Use buildozer -f <file> to load a list of commands from a file. The usage is just like arguments on the command-line, except that arguments are separated by |.

$ cat /tmp/cmds
new cc_library foo|//buildtools/buildozer/BUILD
add deps //base //strings|add srcs|//buildtools/buildozer:foo
add deps :foo|//buildtools/buildozer

$ buildozer -f /tmp/cmds
fixed //buildtools/buildozer/BUILD

The list of commands will typically be generated and can be large. This is efficient: Commands are grouped so that each file is modified once. Files are processed in parallel.

Error code

The return code is:

  • 0 on success, if changes were made
  • 1 when there is a usage error
  • 2 when at least one command has failed
  • 3 on success, when no changes were made

Source Structure

  • buildozer/main.go : Entry point for the buildozer binary
  • edit/buildozer.go : Implementation of functions for the buildozer commands
  • edit/edit.go: Library functions to perform various operations on ASTs. These
  • functions are called by the impl functions in buildozer.go
  • edit/fix.go: Functions for various fixes for the buildozer 'fix <fix(es)>' command, like cleaning unused loads, changing labels to canonical notation, etc.
  • edit/types.go: Type information for attributes
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