Fix #1585 #1547 (#1624)

tools/goctl/pkg/golang/bin.go

@@ -11,10 +11,10 @@ import (
 // GoBin returns a path of GOBIN.
 func GoBin() string {
 	def := build.Default
-	goroot := os.Getenv("GOROOT")
+	goroot := os.Getenv("GOPATH")
 	bin := filepath.Join(goroot, "bin")
 	if !pathx.FileExists(bin) {
-		gopath := os.Getenv("GOPATH")
+		gopath := os.Getenv("GOROOT")
 		bin = filepath.Join(gopath, "bin")
 	}
 	if !pathx.FileExists(bin) {

tools/goctl/pkg/protocgengo/protocgengo.go

@@ -23,8 +23,11 @@ func Install(cacheDir string) (string, error) {
 }
 
 func Exists() bool {
-	_, err := env.LookUpProtocGenGo()
-	return err == nil
+	ver, err := Version()
+	if err != nil {
+		return false
+	}
+	return len(ver) > 0
 }
 
 // Version is used to get the version of the protoc-gen-go plugin. For older versions, protoc-gen-go does not support