Update proxy.go

Author: lychung83

cmd/cloud_sql_proxy/proxy.go

@@ -337,11 +337,19 @@ func CreateInstanceConfigs(dir string, useFuse bool, instances []string, instanc
 		return nil, nil
 	}
 	// FUSE disabled.
-	if len(instances) == 0 && instancesSrc == "" {
-		if fuse.Supported() {
-			return nil, errors.New("must specify -projects, -fuse, or -instances")
-		}
-		return nil, errors.New("must specify -projects or -instances")
-	}
+        if len(instances) == 0 && instancesSrc == "" { 
+                var flags string 
+                if fuse.Supported() { 
+                        flags = "-projects, -fuse, or -instances" 
+                } else { 
+                        flags = "-projects or -instances" 
+                } 
+ 
+                errStr := fmt.Sprintf("no instance selected because none of %s is specified", flags)
+                if gcloudErrStr != "" { 
+                        errStr = fmt.Sprintf("%s and %s", errStr, gcloudErrStr) 
+                } 
+                return nil, errors.New(errStr) 
+        }
 	return cfgs, nil
 }