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") {

[brettw, 2014/09/24 19:25:45]

This needs documentation. What variables does it expect and what do they mean.
Are they optional?

[tburkard, 2014/09/26 13:31:09]

Done.

+  # Only available on linux for now.
+  assert(is_linux)
+  assert(defined(invoker.sources))
+  assert(go_build_tool != "")
+
+  static_library_name = target_name + "_static_library"
+
+  static_library(static_library_name) {
+    sources = invoker.additional_sources

[brettw, 2014/09/24 19:25:45]

This requires "additional_sources" be set. Will there always be additional
sources? That isn't implied to me in the name. I believe static libs will get
confused if there are no sources. Do we need to handle these?

[tburkard, 2014/09/26 13:31:09]

In general, I think any mojo code will require interfacing with C code, so I
think it's ok to require this. However, I agree with you on the name, so I
renamed it to something more descriptive.

Optionally, we could permit having no static_library_sources, but do you know
how this could be done? If not, we can punt on this for now and require it.

Thanks.

+    deps = invoker.deps
+    complete_static_lib = true
+  }
+
+  action(target_name) {
+    deps = [
+      ":$static_library_name",
+    ]
+    script = "//build/go/go.py"
+    outputs = [ "${target_out_dir}/${target_name}" ]
+    # Since go test does not permit specifying an output directory or output
+    # binary name, we create a temporary build directory, and the python
+    # script will later identify the output, copy it to the target location,
+    # and clean up the temporary build directory.
+    build_dir = "${target_out_dir}/${target_name}_build"
+    args = [
+      "--", 
+      "${go_build_tool}",
+      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(target_out_dir) +
+      " -L" + rebase_path(root_build_dir + "/obj/third_party/libevent") +
+      " -l" + static_library_name +
+      " -lstdc++ -lpthread -lm -lglib-2.0 -levent",
+      "test", "-c",
+    ] + rebase_path(invoker.sources, build_dir)
+  }
+}