cmd/go: check GOROOT directory is present before acting

Fixes #5042.

R=golang-dev, adg, rsc
CC=golang-dev
https://golang.org/cl/7786047

diff --git a/src/cmd/go/main.go b/src/cmd/go/main.go
index 3180dbeed2489b476d6505af213a3c9571442ca0..a09a75cd3ec8fe25c3910dafae4b73c0d796a0d3 100644 (file)
--- a/src/cmd/go/main.go
+++ b/src/cmd/go/main.go
@@ -144,6 +144,11 @@ func main() {
                }
        }
 
+       if fi, err := os.Stat(goroot); err != nil || !fi.IsDir() {
+               fmt.Fprintf(os.Stderr, "go: cannot find GOROOT directory: %v\n", goroot)
+               os.Exit(2)
+       }
+
        for _, cmd := range commands {
                if cmd.Name() == args[0] && cmd.Run != nil {
                        cmd.Flag.Usage = func() { cmd.Usage() }