Allow value splitting pattern to be customized

flagset.go

@@ -302,7 +302,7 @@ func (f *FlagSetFiller) processStringSlice(fieldRef interface{}, hasDefaultTag b
 		_ = f.processCustom(
 			fieldRef,
 			func(s string) (interface{}, error) {
-				return parseStringSlice(s), nil
+				return parseStringSlice(s, f.options.valueSplitPattern), nil
 			},
 			hasDefaultTag,
 			tagDefault,
@@ -314,12 +314,20 @@ func (f *FlagSetFiller) processStringSlice(fieldRef interface{}, hasDefaultTag b
 		return
 	}
 	if hasDefaultTag {
-		*casted = parseStringSlice(tagDefault)
+		*casted = parseStringSlice(tagDefault, f.options.valueSplitPattern)
 	}
-	flagSet.Var(&strSliceVar{ref: casted, override: override}, renamed, usage)
+	flagSet.Var(&strSliceVar{
+		ref:               casted,
+		override:          override,
+		valueSplitPattern: f.options.valueSplitPattern,
+	}, renamed, usage)
 	if aliases != "" {
 		for _, alias := range strings.Split(aliases, ",") {
-			flagSet.Var(&strSliceVar{ref: casted, override: override}, alias, usage)
+			flagSet.Var(&strSliceVar{
+				ref:               casted,
+				override:          override,
+				valueSplitPattern: f.options.valueSplitPattern,
+			}, alias, usage)
 		}
 	}
 }
@@ -634,8 +642,9 @@ func (f *FlagSetFiller) processCustom(fieldRef interface{}, converter func(strin
 }
 
 type strSliceVar struct {
-	ref      *[]string
-	override bool
+	ref               *[]string
+	override          bool
+	valueSplitPattern string
 }
 
 func (s *strSliceVar) String() string {
@@ -646,7 +655,7 @@ func (s *strSliceVar) String() string {
 }
 
 func (s *strSliceVar) Set(val string) error {
-	parts := parseStringSlice(val)
+	parts := parseStringSlice(val, s.valueSplitPattern)
 
 	if s.override {
 		*s.ref = parts
@@ -658,8 +667,12 @@ func (s *strSliceVar) Set(val string) error {
 	return nil
 }
 
-func parseStringSlice(val string) []string {
-	splitter := regexp.MustCompile("[\n,]")
+func parseStringSlice(val string, valueSplitPattern string) []string {
+	if valueSplitPattern == "" {
+		return []string{val}
+	}
+
+	splitter := regexp.MustCompile(valueSplitPattern)
 	parts := splitter.Split(val, -1)
 
 	// trim out blank parts

flagset_test.go

@@ -572,6 +572,29 @@ func TestStringSlice(t *testing.T) {
 	assert.Equal(t, []string{"three"}, config.TagOverride)
 }
 
+func TestStringSliceWithEmptyValuePattern(t *testing.T) {
+	type Config struct {
+		NoDefault  []string
+		TagDefault []string `default:"one,two"`
+	}
+
+	var config Config
+	filler := flagsfiller.New(flagsfiller.WithValueSplitPattern(""))
+
+	var flagset flag.FlagSet
+	err := filler.Fill(&flagset, &config)
+	require.NoError(t, err)
+
+	err = flagset.Parse([]string{
+		"--no-default", "nd1,nd2",
+		"--no-default", "nd3",
+	})
+	require.NoError(t, err)
+
+	assert.Equal(t, []string{"nd1,nd2", "nd3"}, config.NoDefault)
+	assert.Equal(t, []string{"one,two"}, config.TagDefault)
+}
+
 func TestStringToStringMap(t *testing.T) {
 	type Config struct {
 		NoDefault       map[string]string

options.go

@@ -13,9 +13,10 @@ var DefaultFieldRenamer = KebabRenamer()
 type FillerOption func(opt *fillerOptions)
 
 type fillerOptions struct {
-	fieldRenamer []Renamer
-	envRenamer   []Renamer
-	noSetFromEnv bool
+	fieldRenamer      []Renamer
+	envRenamer        []Renamer
+	noSetFromEnv      bool
+	valueSplitPattern string
 }
 
 // WithFieldRenamer declares an option to customize the Renamer used to convert field names
@@ -51,6 +52,14 @@ func NoSetFromEnv() FillerOption {
 	}
 }
 
+// WithValueSplitPattern allows for changing the default value splitting regex pattern from newlines and commas.
+// Any empty string can be provided for pattern to disable value splitting.
+func WithValueSplitPattern(pattern string) FillerOption {
+	return func(opt *fillerOptions) {
+		opt.valueSplitPattern = pattern
+	}
+}
+
 func (o *fillerOptions) renameLongName(name string) string {
 	if len(o.fieldRenamer) == 0 {
 		return DefaultFieldRenamer(name)
@@ -63,7 +72,9 @@ func (o *fillerOptions) renameLongName(name string) string {
 }
 
 func newFillerOptions(options ...FillerOption) *fillerOptions {
-	v := &fillerOptions{}
+	v := &fillerOptions{
+		valueSplitPattern: "[\n,]",
+	}
 	for _, opt := range options {
 		opt(v)
 	}