BUILD

load("//skylark:gofmt.bzl", "gofmt")
gofmt(name="gofmt")

gofmt.bzl

def _gofmt_impl(ctx):
  result = ctx.new_file(ctx.label.name)
  workspace = ctx.file._workspace
  gofmt = ctx.executable._gofmt
  options = ctx.attr.options
  target = " ".join(ctx.attr.target)
  ctx.file_action(output=result, executable=True, content="""#!/bin/bash
WORKSPACE=$(dirname $(readlink {workspace}))
cd "$WORKSPACE"
file {gofmt}
echo {gofmt} {options} {target}
""".format(
    gofmt=gofmt.path,
    workspace=workspace.short_path,
    options=options,
    target=target,
  ))
  return [DefaultInfo(runfiles=ctx.runfiles([workspace, gofmt]))]

gofmt = rule(
  implementation = _gofmt_impl,
  executable=True,
  attrs = {
    "options": attr.string(default = "-l -w"),
    "target": attr.string_list(default=["exe", "lib"]),
    "_gofmt": attr.label(cfg="host", executable=True, default=Label("@go_sdk//:bin/gofmt")),
     "_workspace": attr.label(allow_single_file = True, default = Label("//:WORKSPACE")),
  },
)

output

➜ bazel run :gofmt
ERROR: XXX/BUILD:18:1: in (an implicit dependency) attribute of gofmt rule //:gofmt: file '@go_sdk//:bin/gofmt' is misplaced here (expected no files).
ERROR: Analysis of target '//:gofmt' failed; build aborted: Analysis of target '//:gofmt' failed; build aborted.
INFO: Elapsed time: 0.135s
ERROR: Build failed. Not running target.

WORKSPACE

git_repository(
    name = "io_bazel_rules_go",
    remote = "https://github.com/bazelbuild/rules_go.git",
    commit = "3fd320621566c44aad0f7df5d0f5858efd2bbcf6",
)
load("@io_bazel_rules_go//go:def.bzl", "go_rules_dependencies", "go_register_toolchains")
go_rules_dependencies()
go_register_toolchains(go_version="1.9.2")