github.com/bazelbuild/rules_go

Go rules for Bazel_

.. Links to external sites and pages .. _//tests/core/cross: https://github.com/bazelbuild/rules_go/blob/master/tests/core/cross/BUILD.bazel .. _Avoiding conflicts: proto/core.rst#avoiding-conflicts .. _Bazel labels: https://docs.bazel.build/versions/master/build-ref.html#labels .. _Bazel: https://bazel.build/ .. _Bazel Tutorial: Build a Go Project: https://bazel.build/start/go .. _Build modes: go/modes.rst .. _Bzlmod: https://bazel.build/external/overview#bzlmod .. _Go with Bzlmod: docs/go/core/bzlmod.md .. _Go with WORKSPACE: docs/go/core/workspace.md .. _Core rules: docs/go/core/rules.md .. _Coverage: https://bazel.google.cn/docs/coverage .. _Dependencies: go/dependencies.rst .. _Deprecation schedule: https://github.com/bazelbuild/rules_go/wiki/Deprecation-schedule .. _examples/basic_gazelle: examples/basic_gazelle .. _examples/hello: examples/hello .. _Gopher Slack: https://invite.slack.golangbridge.org/ .. _gopls integration: https://github.com/bazelbuild/rules_go/wiki/Editor-setup .. _Overriding dependencies: go/dependencies.rst#overriding-dependencies .. _Proto rules: proto/core.rst .. _Protocol buffers: proto/core.rst .. _Toolchains: go/toolchains.rst .. _Using rules_go on Windows: windows.rst .. _bazel-go-discuss: https://groups.google.com/forum/#!forum/bazel-go-discuss .. _configuration transition: https://docs.bazel.build/versions/master/skylark/lib/transition.html .. _gazelle update-repos: https://github.com/bazelbuild/bazel-gazelle#update-repos .. _gazelle: https://github.com/bazelbuild/bazel-gazelle .. _github.com/bazelbuild/bazel-gazelle: https://github.com/bazelbuild/bazel-gazelle .. _github.com/bazelbuild/rules_go/go/tools/bazel: https://pkg.go.dev/github.com/bazelbuild/rules_go/go/tools/bazel?tab=doc .. _nogo build-time static analysis: go/nogo.rst .. _nogo: go/nogo.rst .. _rules_go and Gazelle roadmap: https://github.com/bazelbuild/rules_go/wiki/Roadmap .. _#bazel on Go Slack: https://gophers.slack.com/archives/C1SCQE54N .. _#go on Bazel Slack: https://bazelbuild.slack.com/archives/CDBP88Z0D

.. Go rules .. _go_binary: docs/go/core/rules.md#go_binary .. _go_context: go/toolchains.rst#go_context .. _go_deps: https://github.com/bazel-contrib/bazel-gazelle/blob/master/extensions.md#go_deps .. _go_download_sdk: go/toolchains.rst#go_download_sdk .. _go_host_sdk: go/toolchains.rst#go_host_sdk .. _go_library: docs/go/core/rules.md#go_library .. _go_local_sdk: go/toolchains.rst#go_local_sdk .. _go_path: docs/go/core/rules.md#go_path .. _go_proto_compiler: proto/core.rst#go_proto_compiler .. _go_proto_library: proto/core.rst#go_proto_library .. _go_register_toolchains: go/toolchains.rst#go_register_toolchains .. _go_repository: https://github.com/bazelbuild/bazel-gazelle/blob/master/reference.md#go_repository .. _go_rules_dependencies: go/dependencies.rst#go_rules_dependencies .. _go_source: docs/go/core/rules.md#go_source .. _go_test: docs/go/core/rules.md#go_test .. _go_cross_binary: docs/go/core/rules.md#go_cross_binary .. _go_toolchain: go/toolchains.rst#go_toolchain .. _go_wrap_sdk: go/toolchains.rst#go_wrap_sdk .. _gomock: docs/go/extras/extras.md#gomock

.. External rules .. _git_repository: https://docs.bazel.build/versions/master/repo/git.html .. _http_archive: https://docs.bazel.build/versions/master/repo/http.html#http_archive .. _proto_library: https://github.com/bazelbuild/rules_proto

.. Issues .. _#265: https://github.com/bazelbuild/rules_go/issues/265 .. _#721: https://github.com/bazelbuild/rules_go/issues/721 .. _#889: https://github.com/bazelbuild/rules_go/issues/889 .. _#1199: https://github.com/bazelbuild/rules_go/issues/1199 .. _#2775: https://github.com/bazelbuild/rules_go/issues/2775

Mailing list: bazel-go-discuss_

Slack: #go on Bazel Slack, #bazel on Go Slack

Contents

• Overview_
• Setup_
• FAQ_

Documentation

* `Core rules`_

  * `go_binary`_
  * `go_library`_
  * `go_test`_
  * `go_source`_
  * `go_path`_
  * `go_cross_binary`_

* `Proto rules`_

  * `go_proto_library`_
  * `go_proto_compiler`_

* `Dependencies`_

  * `go_rules_dependencies`_
  * `go_repository`_ (Gazelle)

* `Toolchains`_

  * `go_register_toolchains`_
  * `go_download_sdk`_
  * `go_host_sdk`_
  * `go_local_sdk`_
  * `go_wrap_sdk`_
  * `go_toolchain`_
  * `go_context`_

* `Extra rules <docs/go/extras/extras.md>`_

  * `gomock`_

* `nogo build-time static analysis`_
* `Build modes <go/modes.rst>`_

Quick links
~~~~~~~~~~~

* `rules_go and Gazelle roadmap`_
* `Deprecation schedule`_
* `Using rules_go on Windows`_

Overview
--------

These rules support:

* Building libraries, binaries, and tests (`go_library`_, `go_binary`_,
  `go_test`_)
* Go modules via `go_deps`_.
* Vendoring
* cgo
* Cross-compilation
* Generating BUILD files via gazelle_
* Build-time static code analysis via nogo_
* `Protocol buffers`_
* Remote execution
* `Coverage`_
* `gopls integration`_ for editor support
* Debugging

They currently do not support or have limited support for:

* C/C++ integration other than cgo (SWIG)

The Go rules are tested and supported on the following host platforms:

* Linux, macOS, Windows
* amd64, arm64

Users have reported success on several other platforms, but the rules are
only tested on those listed above.

Note: Since version v0.51.0, rules_go requires Bazel ≥ 6.5.0 to work.

The ``master`` branch is only guaranteed to work with the latest version of Bazel.


Setup
-----

To build Go code with Bazel, you will need:

* A recent version of Bazel.
* A C/C++ toolchain (if using cgo). Bazel will attempt to configure the
  toolchain automatically.
* Bash, ``patch``, ``cat``, and a handful of other Unix tools in ``PATH``.

You normally won't need a Go toolchain installed. Bazel will download one.

See `Using rules_go on Windows`_ for Windows-specific setup instructions.
Several additional tools need to be installed and configured.

If you're new to Bazel, read `Bazel Tutorial: Build a Go Project`_, which
introduces Bazel concepts and shows you how to set up a small Go workspace to
be built with Bazel.

For a quicker "hello world" example, see `examples/hello`_.

For an example that generates build files and retrieves external dependencies
using Gazelle, see `examples/basic_gazelle`_.

For more detailed `Bzlmod`_ documentation, see `Go with Bzlmod`_.

For legacy ``WORKSPACE`` instructions, see `Go with WORKSPACE`_.

FAQ
---

**Go**

* `Can I still use the go command?`_
* `Does this work with Go modules?`_
* `What's up with the go_default_library name?`_
* `How do I cross-compile?`_
* `How do I access testdata?`_
* `How do I access go_binary executables from go_test?`_

**Protocol buffers**

* `How do I avoid conflicts with protocol buffers?`_
* `Can I use a vendored gRPC with go_proto_library?`_

**Dependencies and testing**

* `How do I use different versions of dependencies?`_
* `How do I test a beta version of the Go SDK?`_

Can I still use the go command?

Yes, but not directly.

rules_go invokes the Go compiler and linker directly, based on the targets described with go_binary_ and other rules. Bazel and rules_go together fill the same role as the go command, so it's not necessary to use the go command in a Bazel workspace.

That said, it's usually still a good idea to follow conventions required by the go command (e.g., one package per directory, package paths match directory paths). Tools that aren't compatible with Bazel will still work, and your project can be depended on by non-Bazel projects.

If you need to use the go command to perform tasks that Bazel doesn't cover (such as adding a new dependency to go.mod), you can use the following Bazel invocation to run the go binary of the Bazel-configured Go SDK:

.. code:: bash

bazel run @io_bazel_rules_go//go -- <args>

Prefer this to running go directly since it ensures that the version of Go is identical to the one used by rules_go.

Does this work with Go modules?

Yes, but not directly. Bazel ignores ``go.mod`` files, and all package
dependencies must be expressed through ``deps`` attributes in targets
described with `go_library`_ and other rules.

You can download a Go module at a specific version as an external repository
using `go_repository`_, a workspace rule provided by gazelle_. This will also
generate build files using gazelle_.

You can import `go_repository`_ rules from a ``go.mod`` file using
`gazelle update-repos`_.

What's up with the go_default_library name?

This was used to keep import paths consistent in libraries that can be built with go build before the importpath attribute was available.

In order to compile and link correctly, rules_go must know the Go import path (the string by which a package can be imported) for each library. This is now set explicitly with the importpath attribute. Before that attribute existed, the import path was inferred by concatenating a string from a special go_prefix rule and the library's package and label name. For example, if go_prefix was github.com/example/project, for a library //foo/bar:bar, rules_go would infer the import path as github.com/example/project/foo/bar/bar. The stutter at the end is incompatible with go build, so if the label name was go_default_library, the import path would not include it. So for the library //foo/bar:go_default_library, the import path would be github.com/example/project/foo/bar.

Since go_prefix was removed and the importpath attribute became mandatory (see #721), the go_default_library name no longer serves any purpose. We may decide to stop using it in the future (see #265).

How do I cross-compile?

You can cross-compile by setting the ``--platforms`` flag on the command line.
For example:

.. code::

  $ bazel build --platforms=@io_bazel_rules_go//go/toolchain:linux_amd64 //cmd

By default, cgo is disabled when cross-compiling. To cross-compile with cgo,
add a ``_cgo`` suffix to the target platform. You must register a
cross-compiling C/C++ toolchain with Bazel for this to work.

.. code::

  $ bazel build --platforms=@io_bazel_rules_go//go/toolchain:linux_amd64_cgo //cmd

Platform-specific sources with build tags or filename suffixes are filtered
automatically at compile time. You can selectively include platform-specific
dependencies with ``select`` expressions (Gazelle does this automatically).

.. code:: bzl

  go_library(
      name = "foo",
      srcs = [
          "foo_linux.go",
          "foo_windows.go",
      ],
      deps = select({
          "@io_bazel_rules_go//go/platform:linux_amd64": [
              "//bar_linux",
          ],
          "@io_bazel_rules_go//go/platform:windows_amd64": [
              "//bar_windows",
          ],
          "//conditions:default": [],
      }),
  )

To build a specific `go_binary`_ target for a target platform or using a
specific golang SDK version, use the `go_cross_binary`_ rule. This is useful
for producing multiple binaries for different platforms in a single build.

To build a specific `go_test`_ target for a target platform, set the
``goos`` and ``goarch`` attributes on that rule.

You can equivalently depend on a `go_binary`_ or `go_test`_ rule through
a Bazel `configuration transition`_ on ``//command_line_option:platforms``
(there are problems with this approach prior to rules_go 0.23.0).

How do I access testdata?

Bazel executes tests in a sandbox, which means tests don't automatically have access to files. You must include test files using the data attribute. For example, if you want to include everything in the testdata directory:

.. code:: bzl

go_test( name = "foo_test", srcs = ["foo_test.go"], data = glob(["testdata/**"]), importpath = "github.com/example/project/foo", )

By default, tests are run in the directory of the build file that defined them. Note that this follows the Go testing convention, not the Bazel convention followed by other languages, which run in the repository root. This means that you can access test files using relative paths. You can change the test directory using the rundir attribute. See go_test_.

Gazelle will automatically add a data attribute like the one above if you have a testdata directory unless it contains buildable .go files or build files, in which case, testdata is treated as a normal package.

Note that on Windows, data files are not directly available to tests, since test data files rely on symbolic links, and by default, Windows doesn't let unprivileged users create symbolic links. You can use the github.com/bazelbuild/rules_go/go/tools/bazel_ library to access data files.

How do I access go_binary executables from go_test?

The location where ``go_binary`` writes its executable file is not stable across
rules_go versions and should not be depended upon. The parent directory includes
some configuration data in its name. This prevents Bazel's cache from being
poisoned when the same binary is built in different configurations. The binary
basename may also be platform-dependent: on Windows, we add an .exe extension.

To depend on an executable in a ``go_test`` rule, reference the executable
in the ``data`` attribute (to make it visible), then expand the location
in ``args``. The real location will be passed to the test on the command line.
For example:

.. code:: bzl

  go_binary(
      name = "cmd",
      srcs = ["cmd.go"],
  )

  go_test(
      name = "cmd_test",
      srcs = ["cmd_test.go"],
      args = ["$(location :cmd)"],
      data = [":cmd"],
  )

See `//tests/core/cross`_ for a full example of a test that
accesses a binary.

Alternatively, you can set the ``out`` attribute of `go_binary`_ to a specific
filename. Note that when ``out`` is set, the binary won't be cached when
changing configurations.

.. code:: bzl

  go_binary(
      name = "cmd",
      srcs = ["cmd.go"],
      out = "cmd",
  )

  go_test(
      name = "cmd_test",
      srcs = ["cmd_test.go"],
      data = [":cmd"],
  )

How do I avoid conflicts with protocol buffers?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

See `Avoiding conflicts`_ in the proto documentation.

Can I use a vendored gRPC with go_proto_library?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is not supported. When using `go_proto_library`_ with the
``@io_bazel_rules_go//proto:go_grpc`` compiler, an implicit dependency is added
on ``@org_golang_google_grpc//:go_default_library``. If you link another copy of
the same package from ``//vendor/google.golang.org/grpc:go_default_library``
or anywhere else, you may experience conflicts at compile or run-time.

If you're using Gazelle with proto rule generation enabled, imports of
``google.golang.org/grpc`` will be automatically resolved to
``@org_golang_google_grpc//:go_default_library`` to avoid conflicts. The
vendored gRPC should be ignored in this case.

If you specifically need to use a vendored gRPC package, it's best to avoid
using ``go_proto_library`` altogether. You can check in pre-generated .pb.go
files and build them with ``go_library`` rules. Gazelle will generate these
rules when proto rule generation is disabled (add ``# gazelle:proto
disable_global`` to your root build file).

How do I use different versions of dependencies?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

See `Overriding dependencies`_ for instructions on overriding repositories
declared in `go_rules_dependencies`_.

How do I test a beta version of the Go SDK?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

rules_go only supports official releases of the Go SDK. However, you can still
test beta and RC versions by passing a ``version`` like ``"1.16beta1"`` to
`go_register_toolchains`_. See also `go_download_sdk`_.

.. code:: bzl

  load("@io_bazel_rules_go//go:deps.bzl", "go_register_toolchains", "go_rules_dependencies")

  go_rules_dependencies()

  go_register_toolchains(version = "1.17beta1")