cmd/gomobile: version command

Finding the revision info from compiled binary (gomobile) built with
'go get' is not currently possible. What we can do instead is to check
if the current mobile repository found from GOPATH builds the same
binary by running 'go install -x -n' and checking if it outputs any
output. If so, this command prints out the revision info of the
repository. Otherwise, prints 'unknown'.

Sample output:

./gomobile version
gomobile version +27329c5 Wed Jul 22 19:29:08 2015 -0400 (android,ios);
androidSDK=/Users/hakim/Library/Android/sdk/platforms/android-22

./gomobile version
gomobile version unknown

Change-Id: Idc26c8a1dd3b43cc47a5c15ce130e2b97a460cec
Reviewed-on: https://go-review.googlesource.com/12455
Reviewed-by: David Crawshaw <crawshaw@golang.org>

cmd/gomobile/main.go

@@ -133,6 +133,7 @@ var commands = []*command{
 	cmdBuild,
 	cmdInit,
 	cmdInstall,
+	cmdVersion,
 }
 
 type command struct {

cmd/gomobile/version.go

@@ -0,0 +1,80 @@
+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+)
+
+var cmdVersion = &command{
+	run:   runVersion,
+	Name:  "version",
+	Usage: "",
+	Short: "print version",
+	Long: `
+Version prints versions of the gomobile binary and tools
+`,
+}
+
+func runVersion(cmd *command) (err error) {
+	// Check this binary matches the version in golang.org/x/mobile/cmd/gomobile
+	// source code in GOPATH. If they don't match, currently there is no
+	// way to reliably identify the revision number this binary was built
+	// against.
+	version := func() string {
+		bin, err := exec.LookPath(os.Args[0])
+		if err != nil {
+			return ""
+		}
+		bindir := filepath.Dir(bin)
+		cmd := exec.Command("go", "install", "-x", "-n", "golang.org/x/mobile/cmd/gomobile")
+		cmd.Env = append(os.Environ(), "GOBIN="+bindir)
+		out, err := cmd.CombinedOutput()
+		if err != nil || len(out) != 0 {
+			return ""
+		}
+		if rev, err := mobileRepoRevision(); err == nil {
+			return rev
+		}
+		return ""
+	}()
+	if version == "" {
+		fmt.Println("gomobile version unknown")
+		return nil
+	}
+
+	// Supported platforms
+	platforms := "android"
+	if goos == "darwin" {
+		platforms = "android,ios"
+	}
+
+	// ANDROID_HOME, sdk build tool version
+	androidapi, _ := androidAPIPath()
+
+	fmt.Printf("gomobile version %s (%s); androidSDK=%s\n", version, platforms, androidapi)
+	return nil
+}
+
+func mobileRepoRevision() (rev string, err error) {
+	b, err := exec.Command("go", "list", "-f", "{{.Dir}}", "golang.org/x/mobile/app").CombinedOutput()
+	if err != nil {
+		return "", fmt.Errorf("mobile repo not found: %v", err)
+	}
+
+	repo := filepath.Dir(string(b))
+	if err := os.Chdir(repo); err != nil {
+		return "", fmt.Errorf("mobile repo %q not accessible: %v", repo, err)
+	}
+	revision, err := exec.Command("git", "log", "-n", "1", "--format=format: +%h %cd", "HEAD").CombinedOutput()
+	if err != nil {
+		return "", err
+	}
+	return string(bytes.Trim(revision, " \t\r\n")), nil
+}