Visibility controls whether a target can be used (depended on) by targets in other packages. This helps other people distinguish between your library’s public API and its implementation details, and is an important tool to help enforce structure as your workspace grows.
If you need to disable the visibility check (for example when experimenting),
All rule targets have a
visibility attribute that takes a list of labels. One
target is visible to another if they are in the same package, or if they are
granted visibility by one of the labels.
Each label has one of the following forms:
"//visibility:public": Anyone can use this target. (May not be combined with any other specification.)
"//visibility:private": Only targets in this package can use this target. (May not be combined with any other specification.)
"//foo/bar:__pkg__": Grants access to targets defined in
//foo/bar(but not its subpackages). Here,
__pkg__is a special piece of syntax representing all of the targets in a package.
"//foo/bar:__subpackages__": Grants access to targets defined in
//foo/bar, or any of its direct or indirect subpackages. Again,
__subpackages__is special syntax.
"//foo/bar:my_package_group": Grants access to all of the packages named by the given package group.
- Package groups do not support the special
__subpackages__syntax. Within a package group,
"//foo/bar"is equivalent to
"//foo/bar/..."is equivalent to
- Package groups do not support the special
For example, if
//some/package:mytarget has its
visibility set to
[":__subpackages__", "//tests:__pkg__"], then it could be used by any target
that is part of the
//some/package/... source tree, as well as targets defined
//tests/BUILD, but not by targets defined in
As a special case,
package_group targets themselves do not have a
attribute; they are always publicly visible.
Visibility of a rule target
If a rule target does not set the
visibility attribute, its visibility is
given by the
default_visibility that was
specified in the
package statement of the
target’s BUILD file. If there is no such
default_visibility declaration, the
# This target is visible to everyone cc_binary( name = "executable", visibility = ["//visibility:public"], deps = [":library"], ) # This target is visible only to targets declared in the same package cc_library( name = "library", # No visibility -- defaults to private since no # package(default_visibility = ...) was used. ) # This target is visible to targets in package //object and //noun cc_library( name = "subject", visibility = [ "//noun:__pkg__", "//object:__pkg__", ], ) # See package group "//frobber:friends" (below) for who can # access this target. cc_library( name = "thingy", visibility = ["//frobber:friends"], )
# This is the package group declaration to which target # //frobber/bin:thingy refers. # # Our friends are packages //frobber, //fribber and any # subpackage of //fribber. package_group( name = "friends", packages = [ "//fribber/...", "//frobber", ], )
Visibility of a file target
By default, file targets are visible only from the same package. To make a file
accessible from another package, use
If the call to
exports_files specifies the visibility attribute, that
visibility applies. Otherwise, the file is public (the
When possible, prefer exposing a library or another type of rule instead of a
source file. For example, declare a
java_library instead of exporting a
.java file. It’s good form for a rule target to only directly include sources
in its own package.
cc_binary( name = "my-program", data = ["//frobber/data:readme.txt"], )
If the flag
is not set, a legacy behavior applies instead.
With the legacy behavior, files used by at least one rule target in the package
are implicitly exported using the
default_visibility specification. See the
for more details.
Visibility of bzl files
load statements are currently not subject to visibility. It is possible to
bzl file anywhere in the workspace.
Visibility of implicit dependencies
Some rules have implicit dependencies. For example, a C++ rule might implicitly depend on a C++ compiler.
Currently, implicit dependencies are treated like normal dependencies. They need
to be visible by all instances of the rule. This behavior can be changed using
Avoid setting the default visibility to public. It may be convenient for prototyping or in small codebases, but it is discouraged in large codebases: try to be explicit about which targets are part of the public interface.
package_groupto share the visibility specifications among multiple targets. This is especially useful when targets in many BUILD files should be exposed to the same set of packages.
Use fine-grained visibility specifications when deprecating a target. Restrict the visibility to the current users to avoid new dependencies.