How to use Bazel to compile multiple platform target at once?

Question

compile single platform:

# BUILD
load("@io_bazel_rules_go//go:def.bzl", "go_binary")
go_binary(
      name = 'example',
      srcs = glob(["src/*.go"]),
)

It can compile normally, but when I want to compile multiple platforms, only this way:

bazel build --platforms=@io_bazel_rules_go//go/toolchain:linux_amd64 //:example
bazel build --platforms=@io_bazel_rules_go//go/toolchain:linux_386 //:example
bazel build --platforms=@io_bazel_rules_go//go/toolchain:windows_amd64 //:example
bazel build --platforms=@io_bazel_rules_go//go/toolchain:darwin_amd64 //:example

I want compile multiple platform target on once,so I try this:

# BUILD
load("//:matrix.bzl", "build_all_platform")


build_all_platform(
    name = 'example',
    pkg = glob(["src/*.go"]),
)

# matrix.bzl
load("@io_bazel_rules_go//go:def.bzl", "go_binary")

SUPPORTED_MATRIX = [
  ("windows", "amd64"),
  ("darwin", "amd64"),
  ("linux", "amd64"),
  ("linux", "386"),
]

def _build(ctx):
    for goos, goarch in SUPPORTED_MATRIX:
        target_name = 'proxy-download-' + goos + '-' + goarch
        if goos == 'windows':
            target_name += '.exe'

        go_binary(
            name = target_name,
            srcs = ctx.attr.pkg,
            pure = "auto",
            goos = goos,
            goarch = goarch,
        )

build_all_platform = rule(
    _build,
     attrs = {
        'pkg': attr.string_list(),
      },
      executable = True,
)

But encountered an error, I think this may be the reason for rules_go.

Traceback (most recent call last):
    File "/source/proxy-download/BUILD", line 4
        build_all_platform(name = 'proxy-download')
    File "/source/proxy-download/matrix.bzl", line 16, in _build
        go_binary(name = target_name, <4 more arguments>)
    File "/private/var/tmp/_bazel_/071099b99a462d431baf96a3ef76cd28/external/io_bazel_rules_go/go/private/rules/wrappers.bzl", line 50, in go_binary
        go_transition_wrapper(go_binary, <3 more arguments>)
    File "/private/var/tmp/_bazel_/071099b99a462d431baf96a3ef76cd28/external/io_bazel_rules_go/go/private/rules/transition.bzl", line 60, in go_transition_wrapper
        transition_kind(name = name, <1 more arguments>)
'rule' can only be called during the loading phase

Try to pass multiple platforms at the same time mentioned in this issue

bazel build --platforms=@io_bazel_rules_go//go/toolchain:linux_386,@io_bazel_rules_go//go/toolchain:linux_amd64 //:example

> WARNING: --platforms only supports a single target platform: using the first option @io_bazel_rules_go//go/toolchain:linux_386

For reference, this code implements this by using the build command line

options = [
    "go",
    "build",
    "-o", output_file.path,
    "-compiler", "gc",
    "-gcflags", '"all=-trimpath=${GOPATH}/src"',
    "-asmflags", '"all=-trimpath=${GOPATH}/src"',
    "-ldflags", "'%s'" % ld_flags,
    "-tags", "'%s'" % ctx.attr.gotags,
    pkg,
  ]

Answer 1

You may want to take a look at Bazel's user defined transitions that can build dependencies using different build configurations. Note that it's an experimental feature and not all build parameters are configurable.