Support build stamp in go_binary

If the stamp attribute is true in go_binary,
bazel-out/volatile-status.txt and stable-status.txt will be
concatenated and written into the binary using a -X linker flag.

Developers can access stamp information by adding a dependency on
@io_bazel_rules_go//buildstamp:go_default_library.

Fixes bazelbuild#233

README.md

@@ -457,7 +457,7 @@ go_library(
 ## go\_binary
 
 ```bzl
-go_binary(name, srcs, deps, data)
+go_binary(name, srcs, deps, data, stamp)
 ```
 <table class="table table-condensed table-bordered table-params">
   <colgroup>
@@ -499,6 +499,20 @@ go_binary(name, srcs, deps, data)
         <p>List of files needed by this rule at runtime.</p>
       </td>
     </tr>
+    <tr>
+      <td><code>stamp</code></td>
+      <td>
+        <code>Boolean; optional; default is False</code>
+        <p>Whether build information should be included in the generated binary.
+        Add <code>@io_bazel_rules_go//buildstamp:go_default_library</code> to
+        <code>deps</code> to access the build information . Build with 
+        <code>--workspace_status_command=./status.sh</code> to add custom
+        information (using your own script).
+        <a href="https://github.com/bazelbuild/bazel/blob/master/tools/buildstamp/get_workspace_status">
+        tools/buildstamp/get_workspace_status</a> in Bazel is a good template
+        for this that provides the Git revision and status.
+      </td>
+    </tr>
   </tbody>
 </table>
 

buildstamp/BUILD

@@ -0,0 +1,9 @@
+load("//go:def.bzl", "go_library", "go_prefix")
+
+go_prefix("github.com/bazelbuild/rules_go")
+
+go_library(
+    name = "go_default_library",
+    srcs = glob(["*.go"]),
+    visibility = ["//visibility:public"],
+)

buildstamp/buildstamp.go

@@ -0,0 +1,53 @@
+package buildstamp
+
+import "strings"
+
+var rawStampData string
+var stampData map[string]string
+
+func init() {
+	if len(rawStampData) > 0 {
+		stampData = make(map[string]string)
+		for _, line := range strings.Split(rawStampData, "\n") {
+			line = strings.TrimSpace(line)
+			if len(line) == 0 || strings.HasPrefix(line, "#") {
+				continue
+			}
+			var key, value string
+			if space := strings.IndexAny(line, " \t"); space == -1 {
+				key = line
+			} else {
+				key = line[:space]
+				value = strings.TrimSpace(line[space+1:])
+			}
+			stampData[key] = value
+		}
+	}
+}
+
+func HaveStampData() bool {
+	return stampData != nil
+}
+
+func RawStampData() string {
+	return rawStampData
+}
+
+func GetStampKeys() []string {
+	if stampData == nil {
+		return nil
+	}
+	keys := make([]string, 0, len(stampData))
+	for k, _ := range stampData {
+		keys = append(keys, k)
+	}
+	return keys
+}
+
+func GetStampValue(key string) (value string, ok bool) {
+	if stampData == nil {
+		return "", false
+	}
+	value, ok = stampData[key]
+	return
+}

go/def.bzl

@@ -352,7 +352,7 @@ def _short_path(f):
   return f.path[len(prefix):]
 
 def emit_go_link_action(ctx, importmap, transitive_libs, cgo_deps, lib,
-                        executable, x_defs={}):
+                        executable, x_defs={}, stamp=False):
   """Sets up a symlink tree to libraries to link together."""
   out_dir = executable.path + ".dir"
   out_depth = out_dir.count('/') + 1
@@ -396,6 +396,15 @@ def emit_go_link_action(ctx, importmap, transitive_libs, cgo_deps, lib,
   if x_defs:
     link_cmd += [" -X %s='%s' " % (k, v) for k,v in x_defs.items()]
 
+  if stamp:
+    stamp_cmd = ("LINKSTAMP=$(cat '%s' '%s')" %
+        (ctx.version_file.path, ctx.info_file.path))    
+    link_cmd += ['-X github.com/bazelbuild/rules_go/buildstamp.rawStampData="$LINKSTAMP"']
+    stamp_deps = [ctx.version_file, ctx.info_file]
+  else:
+    stamp_cmd = ""
+    stamp_deps = []
+
   # workaround for a bug in ld(1) on Mac OS X.
   # http://lists.apple.com/archives/Darwin-dev/2006/Sep/msg00084.html
   # TODO(yugui) Remove this workaround once rules_go stops supporting XCode 7.2
@@ -416,6 +425,7 @@ def emit_go_link_action(ctx, importmap, transitive_libs, cgo_deps, lib,
   cmds += ["export PATH=$PATH:/usr/bin"]
   cmds += [
     "export GOROOT=$(pwd)/" + ctx.file.go_tool.dirname + "/..",
+    stamp_cmd,
     "cd " + out_dir,
     ' '.join(link_cmd),
     "mv -f " + _go_importpath(ctx) + " " + ("../" * out_depth) + executable.path,
@@ -424,7 +434,7 @@ def emit_go_link_action(ctx, importmap, transitive_libs, cgo_deps, lib,
   f = _emit_generate_params_action(cmds, ctx, lib.path + ".GoLinkFile.params")
 
   ctx.action(
-      inputs = (list(transitive_libs) + [lib] + list(cgo_deps) +
+      inputs = (list(transitive_libs) + [lib] + list(cgo_deps) + stamp_deps +
                 ctx.files.toolchain + ctx.files._crosstool),
       outputs = [executable],
       executable = f,
@@ -438,12 +448,13 @@ def go_binary_impl(ctx):
   lib_out = ctx.outputs.lib
 
   emit_go_link_action(
-    ctx,
-    transitive_libs=lib_result.transitive_go_library_object,
-    importmap=lib_result.transitive_go_importmap,
-    cgo_deps=lib_result.transitive_cgo_deps,
-    lib=lib_out, executable=executable,
-    x_defs=ctx.attr.x_defs)
+      ctx,
+      transitive_libs=lib_result.transitive_go_library_object,
+      importmap=lib_result.transitive_go_importmap,
+      cgo_deps=lib_result.transitive_cgo_deps,
+      lib=lib_out, executable=executable,
+      x_defs=ctx.attr.x_defs,
+      stamp=ctx.attr.stamp)
 
   runfiles = ctx.runfiles(collect_data = True,
                           files = ctx.files.data)