Go rules for Bazel

Mailing list: bazel-go-discuss

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

Announcements

2024-07-19

v0.48.1 is now available. This includes a bug fix (#3961).

2024-05-21

v0.48.0 is now available. This release enables support for --incompatible_enable_proto_toolchain_resolution (#3919).

2024-05-06

v0.47.1 is now available. This release includes a bug fix (#3929).

2024-04-23

v0.47.0 is now available. This release includes bug fixes and enhancements.

2024-02-09

v0.46.0 is now available. This release includes a change to emit Nogo facts to a separate archive, and Bzlmod support for Nogo (#3842, #3789).

2024-01-19

v0.45.1 is now available. This release includes a bug fix (#3832).

2024-01-12

v0.45.0 is now available. This release includes bug fixes and enhancements.

2024-01-04

Release v0.44.2 is now available. This includes two bug fixes (#3808 and #3810) with the test timeout handler.

2023-12-29

Release v0.44.1 is now available. This release reverts a forced upgrade (#3803) of genproto from v0.44.0.

2023-12-15

Release v0.44.0 is now available. This release adds a stacktrace when a test times out and adds support for nogo in Bzlmod.

2023-11-20

Release v0.43.0 is now available. This release fixes a couple bugs and upgrades x/tools to the latest version.

2023-09-28

Release v0.42.0 is now available. This release fixes a couple bugs and adds support for patching the standard library.

2023-07-10

Release v0.41.0 is now available. rules_go no longer ship with @go_googleapis repo. It requires Gazelle v0.32.0 or later.

2023-06-28

Release v0.40.1 is now available. This release fixes a couple bugs in the go packages driver that were introduced in 0.40.0.

2023-06-22

Release v0.40.0 is now available. This release includes support for //nolint parsing, as well as a large set of additional changes. Please check the release notes for details.

2023-03-27

Release v0.39.0 is now available. This release includes a simpler interface for Bzlmod go_sdk registration, makes the //go tool available to users, and fixes various bugs.

2022-12-06

Release v0.37.0 is now available. This release includes support for generated code in the packages driver as well as various bugfixes.

2022-11-22

Release v0.36.0 is now available. This release adds a Go library to look up runfiles, and two command line flags to pass additional compiler and linker options.

2022-09-11

Release v0.35.0 is now available. This release supports switching Go SDK version from a build flag. Starting this release, rules_go requires Bazel 5.1.0, because it needs to read CPU architecture from Bazel to better support Apple M1 with Rosetta translation.

2022-07-19

Release v0.34.0 is now available. This release brings very experimental support for bzlmod, several improvements to nogo and gopackagesdriver.

2022-06-06

Release v0.33.0 is now available. This release consists mostly of bug fixes and deprecates the asm, compile, cover, and pack actions on go_context.

2022-05-11

Release v0.32.0 is now available. This adds gomock to rules_go and supports lcov format for code coverage report, as well as a long list of other changes listed in the release notes.

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 * gomock
• nogo build-time static analysis
• Build modes

Quick links

• rules_go and Gazelle roadmap
• Deprecation schedule
• Using rules_go on Windows

Overview

The rules are in the beta stage of development. They support:

• Building libraries, binaries, and tests (go_library, go_binary, go_test)
• Vendoring
• cgo
• Cross-compilation
• Generating BUILD files via gazelle
• Build-time 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

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

System 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.

Initial project setup

There are two ways to setup:

• With Bazel's external dependency management system Bzlmod,

refer to the dedicated Go with Bzlmod guide. * With the older WORKSPACE dependency file, refer to the Go with WORKSPACE setup docs.

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:

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:

$ 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.

$ 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).

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:

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:

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.

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.

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

go_rules_dependencies()

go_register_toolchains(version = "1.17beta1")