parse: fix parsing empty argument for both posix and args

parse/args/args.go

@@ -80,7 +80,7 @@ func (p *Parser) next() bool {
 	name, value, hasValue := split(name, '=')
 	if !hasValue && p.pos < len(p.Args) {
 		value = p.Args[p.pos]
-		if len(value) > 0 && value[0] != '-' {
+		if len(value) == 0 || value[0] != '-' {
 			// NOTE: this is NOT the same behaviour as for flag.Parse().
 			//       flag.Parse() works well if we pass `-flag=true`, but not
 			//       if we pass `-flag true`.

parse/args/args_test.go

@@ -67,6 +67,30 @@ func TestFlagsParseArgs(t *testing.T) {
 				"arg1", "arg2", "arg3",
 			},
 		},
+		{
+			name: "empty arg",
+			flags: map[string]bool{
+				"param": false,
+			},
+			args: []string{
+				"--param",
+				"",
+			},
+			expPairs: [][2]string{
+				{"param", ""},
+			},
+		},
+		{
+			name: "empty bool arg",
+			flags: map[string]bool{
+				"param": true,
+			},
+			args: []string{
+				"--param",
+				"",
+			},
+			err: true,
+		},
 		{
 			name: "basic error",
 			flags: map[string]bool{

parse/pargs/posix.go

@@ -172,7 +172,7 @@ func (p *Parser) next() bool {
 	name, value, hasValue := split(s, '=')
 	if !hasValue && p.pos < len(p.Args) {
 		value = p.Args[p.pos]
-		if len(value) > 0 && value[0] != '-' {
+		if len(value) == 0 || value[0] != '-' {
 			if p.isBoolFlag(name) {
 				dash := "--"
 				if short {

parse/pargs/posix_test.go

@@ -115,6 +115,28 @@ func TestPosixParse(t *testing.T) {
 				{"bar", "false"},
 			},
 		},
+		{
+			name: "empty parameter",
+			args: []string{
+				"--foo", "",
+			},
+			flags: map[string]bool{
+				"foo": false,
+			},
+			expPairs: [][2]string{
+				{"foo", ""},
+			},
+		},
+		{
+			name: "empty boolean",
+			args: []string{
+				"--foo", "",
+			},
+			flags: map[string]bool{
+				"foo": true,
+			},
+			err: true,
+		},
 		{
 			name: "long ambiguous booleans",
 			args: []string{