main: "--" should also block "-o" parsing

Includes test cases.

README.md

@@ -162,6 +162,7 @@ v1.3 (in progress)
 * Use stable 64-bit inode numbers in reverse mode
   * This may cause problems for very old 32-bit applications
     that were compiled without Large File Support.
+* Passing "--" now also block "-o" parsing
 
 v1.2.1, 2017-02-26
 * Add an integrated speed test, `gocryptfs -speed`

cli_args.go

@@ -36,11 +36,19 @@ var flagSet *flag.FlagSet
 
 // prefixOArgs transform options passed via "-o foo,bar" into regular options
 // like "-foo -bar" and prefixes them to the command line.
+// Testcases in TestPrefixOArgs().
 func prefixOArgs(osArgs []string) []string {
-	// Need at least 3, example: gocryptfs -o foo,bar
+	// Need at least 3, example: gocryptfs -o    foo,bar
+	//                               ^ 0    ^ 1    ^ 2
 	if len(osArgs) < 3 {
 		return osArgs
 	}
+	// Passing "--" disables "-o" parsing. Ignore element 0 (program name).
+	for _, v := range osArgs[1:] {
+		if v == "--" {
+			return osArgs
+		}
+	}
 	// Find and extract "-o foo,bar"
 	var otherArgs, oOpts []string
 	for i := 1; i < len(osArgs); i++ {

cli_args_test.go

@@ -12,6 +12,7 @@ type testcase struct {
 	o []string
 }
 
+// TestPrefixOArgs checks that the "-o x,y,z" parsing works correctly.
 func TestPrefixOArgs(t *testing.T) {
 	testcases := []testcase{
 		{
@@ -51,6 +52,15 @@ func TestPrefixOArgs(t *testing.T) {
 			i: []string{"gocryptfs", "-o", "rw", "--config", "fff", "ccc", "mmm"},
 			o: []string{"gocryptfs", "-rw", "--config", "fff", "ccc", "mmm"},
 		},
+		// "--" should also block "-o" parsing.
+		{
+			i: []string{"gocryptfs", "foo", "bar", "--", "-o", "a"},
+			o: []string{"gocryptfs", "foo", "bar", "--", "-o", "a"},
+		},
+		{
+			i: []string{"gocryptfs", "--", "-o", "a"},
+			o: []string{"gocryptfs", "--", "-o", "a"},
+		},
 	}
 	for _, tc := range testcases {
 		o := prefixOArgs(tc.i)