Go rules

The files here demonstrate how to use the rules for Go supplied under //tools/build_rules:go_rules.bzl. The rules should be considered experimental. They support:

• libraries
• binaries
• tests

They currently do not support:

• coverage
• race detector
• multiple target configurations
• //+build tags
• C/C++ interoperation (cgo, swig etc.)

Testing

Setup a symlink to the Go installation you wish to use,

ln -s /usr/lib/golang/ tools/go/go_root

or

ln -s $(go env GOROOT) tools/go/go_root

To build something, run

bazel build examples/go/...

To run a test, run

bazel test --test_arg=--test.v examples/go/lib1:lib1_test

Writing BUILD rules

In the bazel model of compiling Go, each directory can hold multiple packages, rather than just one in the standard “go” tool. Suppose you have

dir/f.go:

package p
func F() {}

then in the BUILD file could say

go_library(
  name = "q",
  srcs = ["f.go"])

and you import it with its Bazel name,

import "dir/p/q"

this add the declared package name as namespace, i.e., it is equivalent to

import p "dir/p/q"

so you use it as follows

import "dir/p/q"
main() {
  p.F()
}

Writing tests

For tests, you should create a separate target,

go_test(
  name = "q_test",
  srcs = [ "f_test.go" ],
  deps = [ ":q" ])

if the test code is in the same package as the library under test (e.g., because you are testing private parts of the library), you should use the library attribute,

go_test(
  name = "q_test",
  srcs = [ "f_test.go" ],
  library = ":q" )

This causes the test and the library under test to be compiled together.

FAQ

Why does this not follow the external Go conventions?

These rules were inspired on Google's internal Go rules, which work like this. For Bazel, these make more sense, because directories in Bazel do not correspond to single targets.

Do I have to specify dependencies twice?

Yes, once in the BUILD file, once in the source file. Bazel does not examine file contents, so it cannot infer the dependencies. It is possible to generate the BUILD file from the Go sources through a separate program, though.

Disclaimer

These rules are not supported by Google's Go team.