From cb3d27d01bbf696929b4d77d10e47eca2693e3fa Mon Sep 17 00:00:00 2001
From: Victor Vieux <victor.vieux@docker.com>
Date: Mon, 3 Mar 2014 19:17:28 +0000
Subject: [PATCH] prevent flag grouping with --

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
---
 pkg/mflag/flag.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/pkg/mflag/flag.go b/pkg/mflag/flag.go
index 7a0e8bfb79..b5c5fa9089 100644
--- a/pkg/mflag/flag.go
+++ b/pkg/mflag/flag.go
@@ -772,6 +772,9 @@ func (f *FlagSet) parseOne() (bool, string, error) {
 			f.usage()
 			return false, "", ErrHelp
 		}
+		if len(name) > 0 && name[0] == '-' {
+			return false, "", f.failf("flag provided but not defined: -%s", name)
+		}
 		return false, name, ErrRetry
 	}
 	if fv, ok := flag.Value.(boolFlag); ok && fv.IsBoolFlag() { // special case: doesn't need an arg