fix: handle contents of tags properly by unquoting them when necessary

kong_test.go

@@ -8,8 +8,9 @@ import (
 	"testing"
 
 	"github.com/alecthomas/assert/v2"
-	"github.com/alecthomas/kong"
 	"github.com/alecthomas/repr"
+
+	"github.com/alecthomas/kong"
 )
 
 func mustNew(t *testing.T, cli interface{}, options ...kong.Option) *kong.Kong {

tag.go

@@ -56,11 +56,13 @@ func (t *Tag) String() string {
 
 type tagChars struct {
 	sep, quote, assign rune
+	needsUnquote       bool
 }
 
-var kongChars = tagChars{sep: ',', quote: '\'', assign: '='}
-var bareChars = tagChars{sep: ' ', quote: '"', assign: ':'}
+var kongChars = tagChars{sep: ',', quote: '\'', assign: '=', needsUnquote: false}
+var bareChars = tagChars{sep: ' ', quote: '"', assign: ':', needsUnquote: true}
 
+// nolint:gocyclo
 func parseTagItems(tagString string, chr tagChars) (map[string][]string, error) {
 	d := map[string][]string{}
 	key := []rune{}
@@ -68,11 +70,25 @@ func parseTagItems(tagString string, chr tagChars) (map[string][]string, error)
 	quotes := false
 	inKey := true
 
-	add := func() {
-		d[string(key)] = append(d[string(key)], string(value))
+	add := func() error {
+		// Bare tags are quoted, therefore we need to unquote them in the same fashion reflect.Lookup() (implicitly)
+		// unquotes "kong tags".
+		s := string(value)
+
+		if chr.needsUnquote && s != "" {
+			if unquoted, err := strconv.Unquote(fmt.Sprintf(`"%s"`, s)); err == nil {
+				s = unquoted
+			} else {
+				return fmt.Errorf("unquoting tag value `%s`: %w", s, err)
+			}
+		}
+
+		d[string(key)] = append(d[string(key)], s)
 		key = []rune{}
 		value = []rune{}
 		inKey = true
+
+		return nil
 	}
 
 	runes := []rune(tagString)
@@ -86,7 +102,10 @@ func parseTagItems(tagString string, chr tagChars) (map[string][]string, error)
 			eof = true
 		}
 		if !quotes && r == chr.sep {
-			add()
+			if err := add(); err != nil {
+				return nil, err
+			}
+
 			continue
 		}
 		if r == chr.assign && inKey {
@@ -96,6 +115,12 @@ func parseTagItems(tagString string, chr tagChars) (map[string][]string, error)
 		if r == '\\' {
 			if next == chr.quote {
 				idx++
+
+				// We need to keep the backslashes, otherwise subsequent unquoting cannot work
+				if chr.needsUnquote {
+					value = append(value, r)
+				}
+
 				r = chr.quote
 			}
 		} else if r == chr.quote {
@@ -119,7 +144,9 @@ func parseTagItems(tagString string, chr tagChars) (map[string][]string, error)
 		return nil, fmt.Errorf("%v is not quoted properly", tagString)
 	}
 
-	add()
+	if err := add(); err != nil {
+		return nil, err
+	}
 
 	return d, nil
 }
@@ -242,7 +269,7 @@ func hydrateTag(t *Tag, typ reflect.Type) error { // nolint: gocyclo
 	}
 	t.PlaceHolder = t.Get("placeholder")
 	t.Enum = t.Get("enum")
-	scalarType := (typ == nil || !(typ.Kind() == reflect.Slice || typ.Kind() == reflect.Map || typ.Kind() == reflect.Ptr))
+	scalarType := typ == nil || !(typ.Kind() == reflect.Slice || typ.Kind() == reflect.Map || typ.Kind() == reflect.Ptr)
 	if t.Enum != "" && !(t.Required || t.HasDefault) && scalarType {
 		return fmt.Errorf("enum value is only valid if it is either required or has a valid default value")
 	}

tag_test.go

@@ -5,17 +5,18 @@ import (
 	"testing"
 
 	"github.com/alecthomas/assert/v2"
+
 	"github.com/alecthomas/kong"
 )
 
 func TestDefaultValueForOptionalArg(t *testing.T) {
 	var cli struct {
-		Arg string `kong:"arg,optional,default='👌'"`
+		Arg string `kong:"arg,optional,default='\"\\'👌\\'\"'"`
 	}
 	p := mustNew(t, &cli)
 	_, err := p.Parse(nil)
 	assert.NoError(t, err)
-	assert.Equal(t, "👌", cli.Arg)
+	assert.Equal(t, "\"'👌'\"", cli.Arg)
 }
 
 func TestNoValueInTag(t *testing.T) {
@@ -66,6 +67,18 @@ func TestEscapedQuote(t *testing.T) {
 	assert.Equal(t, "i don't know", cli.DoYouKnow)
 }
 
+func TestEscapingInQuotedTags(t *testing.T) {
+	var cli struct {
+		Regex1 string `kong:"default='\\d+\n'"`
+		Regex2 string `default:"\\d+\n"`
+	}
+	p := mustNew(t, &cli)
+	_, err := p.Parse(nil)
+	assert.NoError(t, err)
+	assert.Equal(t, "\\d+\n", cli.Regex1)
+	assert.Equal(t, "\\d+\n", cli.Regex2)
+}
+
 func TestBareTags(t *testing.T) {
 	var cli struct {
 		Cmd struct {