Fix sep:"none" and mapsep:"none"

According to the README.md, a value of `"none"` for the `sep` tag (for
slices) and `mapsep` (for maps) is meant to disable the separator that
would allow multiple entries to be added from a single argument.
However, using `"none"` just set the separator to the rune `'n'`.

Fix the parsing of the tag, and also update `SplitEscaped` to not split
with a separator of `-1`.

Add a new test for the new cases.

mapper.go

@@ -636,6 +636,9 @@ func urlMapper() MapperFunc {
 //
 //     SplitEscaped(`hello\,there,bob`, ',') == []string{"hello,there", "bob"}
 func SplitEscaped(s string, sep rune) (out []string) {
+	if sep == -1 {
+		return []string{s}
+	}
 	escaped := false
 	token := ""
 	for _, ch := range s {

mapper_test.go

@@ -130,6 +130,7 @@ func TestDurationMapper(t *testing.T) {
 func TestSplitEscaped(t *testing.T) {
 	require.Equal(t, []string{"a", "b"}, kong.SplitEscaped("a,b", ','))
 	require.Equal(t, []string{"a,b", "c"}, kong.SplitEscaped(`a\,b,c`, ','))
+	require.Equal(t, []string{"a,b,c"}, kong.SplitEscaped(`a,b,c`, -1))
 }
 
 func TestJoinEscaped(t *testing.T) {
@@ -172,6 +173,18 @@ func TestMapWithDifferentSeparator(t *testing.T) {
 	require.Equal(t, map[string]string{"a": "b", "c": "d"}, cli.Value)
 }
 
+func TestMapWithNoSeparator(t *testing.T) {
+	var cli struct {
+		Slice []string          `sep:"none"`
+		Value map[string]string `mapsep:"none"`
+	}
+	k := mustNew(t, &cli)
+	_, err := k.Parse([]string{"--slice=a,n,c", "--value=a=b;n=d"})
+	require.NoError(t, err)
+	require.Equal(t, []string{"a,n,c"}, cli.Slice)
+	require.Equal(t, map[string]string{"a": "b;n=d"}, cli.Value)
+}
+
 func TestURLMapper(t *testing.T) {
 	var cli struct {
 		URL *url.URL `arg:""`

tag.go

@@ -151,23 +151,23 @@ func parseTag(fv reflect.Value, ft reflect.StructField) *Tag {
 	t.Short, _ = t.GetRune("short")
 	t.Hidden = t.Has("hidden")
 	t.Format = t.Get("format")
-	t.Sep, _ = t.GetRune("sep")
-	t.MapSep, _ = t.GetRune("mapsep")
 	t.Group = t.Get("group")
 	t.Xor = t.Get("xor")
 	t.Prefix = t.Get("prefix")
 	t.Embed = t.Has("embed")
-	if t.Sep == 0 {
-		if t.Get("sep") == "none" {
-			t.Sep = -1
-		} else {
+	if t.Get("sep") == "none" {
+		t.Sep = -1
+	} else {
+		t.Sep, _ = t.GetRune("sep")
+		if t.Sep == 0 {
 			t.Sep = ','
 		}
 	}
-	if t.MapSep == 0 {
-		if t.Get("mapsep") == "none" {
-			t.MapSep = -1
-		} else {
+	if t.Get("mapsep") == "none" {
+		t.MapSep = -1
+	} else {
+		t.MapSep, _ = t.GetRune("mapsep")
+		if t.MapSep == 0 {
 			t.MapSep = ';'
 		}
 	}