cmd/go: helpful error messages when hg, git, svn, bzr not found #4652
Description
If a vcs tool like hg, git, svn, bzr is not found, cmd/go should explain to the user what to install. See confusion at https://plus.google.com/u/0/115056313943520401920/posts/Xvmwe76BJMS vcs.go currently has just: // run1 is the generalized implementation of run and runOutput. func (v *vcsCmd) run1(dir string, cmdline string, keyval []string, verbose bool) ([]byte, error) { m := make(map[string]string) for i := 0; i < len(keyval); i += 2 { m[keyval[i]] = keyval[i+1] } args := strings.Fields(cmdline) for i, arg := range args { args[i] = expand(m, arg) } cmd := exec.Command(v.cmd, args...) cmd.Dir = dir if buildX { fmt.Printf("cd %s\n", dir) fmt.Printf("%s %s\n", v.cmd, strings.Join(args, " ")) } var buf bytes.Buffer cmd.Stdout = &buf cmd.Stderr = &buf err := cmd.Run() out := buf.Bytes() if err != nil { if verbose || buildV { fmt.Fprintf(os.Stderr, "# cd %s; %s %s\n", dir, v.cmd, strings.Join(args, " ")) os.Stderr.Write(out) } return nil, err } return out, nil } We are more helpful in at at least one other case, as precedent: if toolIsWindows && toolName == "pprof" { args = append([]string{"perl", toolPath}, args[1:]...) var err error toolPath, err = exec.LookPath("perl") if err != nil { fmt.Fprintf(os.Stderr, "go tool: perl not found\n") setExitStatus(3) return } }