Add Go build support for GN.

build/go/rules.gni

+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+declare_args() {
+  # By default, there is no go build tool, because go builds are not supported.
+  go_build_tool = ""
+}
+
+template("go_test_binary") {
+  # Only available on linux for now.
+  assert(is_linux)
+  assert(defined(invoker.sources))
+#  assert(defined(invoker.go_base_module))
+  assert(go_build_tool != "")
+
+  if (go_build_tool != "") {
+    action(target_name) {
+      script = "//build/go/go.py"

[qsr, 2014/09/15 09:54:24]

If you really cannot declare the target binary, then you should work in a
temporary directory, and then find you executable and move it in the final
location in the build_dir. You should have all of this generated by this
template.

[brettw, 2014/09/16 22:58:55]

I don't understand what you're saying here.

[tburkard, 2014/09/17 12:06:45]

That's what I'm doing, I am creating the _build direcotry, perform the build in
there, and then move the executable that was generated back to the target out
dir. The python script is locating the file and copying it. I don't think I can
do this in gn because I do not know the name of the output file. That's why I am
doing it in python.

+      outputs = [ "${target_out_dir}/${target_name}" ]
+      build_dir = "${target_out_dir}/${target_name}_build"
+      args = [
+        "${go_build_tool}",

[brettw, 2014/09/16 22:58:54]

Can you comment about this rule what this go test thingy is doing? Why do you
need a separate build dir for this target? Generally the target_out_dir should
be sufficient, but depending on how thin gs work, maybe not.

[tburkard, 2014/09/17 12:06:45]

Explained why I am doing it this way in the comment that I just added.

+        rebase_path(build_dir, root_build_dir),
+        rebase_path(target_out_dir, root_build_dir) + "/${target_name}",
+        rebase_path("//", root_build_dir),
+        "-I" + rebase_path("//", "//"),
+        "-L" + rebase_path("//out/Release/lib", "//") +
+        " -lmojo_system_impl -lbase",
+        "test", "-c",
+      ] + rebase_path(invoker.sources, build_dir)
+    }
+  }
+}