Clear reference values (maps and slices) when first set

Fixes #323.

ini.go

@@ -499,6 +499,10 @@ func (i *IniParser) matchingGroups(name string) []*Group {
 func (i *IniParser) parse(ini *ini) error {
 	p := i.parser
 
+	p.eachOption(func(cmd *Command, group *Group, option *Option) {
+		option.clearReferenceBeforeSet = true
+	})
+
 	var quotesLookup = make(map[*Option]bool)
 
 	for name, section := range ini.Sections {

ini_test.go

@@ -971,6 +971,30 @@ func TestIniRequired(t *testing.T) {
 	assertString(t, opts.Required, "cli-value")
 }
 
+func TestIniRequiredSlice_ShouldNotNeedToBeSpecifiedOnCli(t *testing.T) {
+	type options struct {
+		Items []string `long:"item" required:"true"`
+	}
+	var opts options
+	ini := `
+[Application Options]
+item=abc`
+	args := []string{}
+
+	parser := NewParser(&opts, Default)
+	inip := NewIniParser(parser)
+
+	inip.Parse(strings.NewReader(ini))
+
+	_, err := parser.ParseArgs(args)
+
+	if err != nil {
+		t.Fatalf("Unexpected failure: %v", err)
+	}
+
+	assertString(t, opts.Items[0], "abc")
+}
+
 func TestWriteFile(t *testing.T) {
 	file, err := ioutil.TempFile("", "")
 	if err != nil {

option.go

@@ -80,10 +80,11 @@ type Option struct {
 	// Determines if the option will be always quoted in the INI output
 	iniQuote bool
 
-	tag            multiTag
-	isSet          bool
-	isSetDefault   bool
-	preventDefault bool
+	tag                     multiTag
+	isSet                   bool
+	isSetDefault            bool
+	preventDefault          bool
+	clearReferenceBeforeSet bool
 
 	defaultLiteral string
 }
@@ -241,12 +242,13 @@ func (option *Option) IsSetDefault() bool {
 func (option *Option) set(value *string) error {
 	kind := option.value.Type().Kind()
 
-	if (kind == reflect.Map || kind == reflect.Slice) && !option.isSet {
+	if (kind == reflect.Map || kind == reflect.Slice) && option.clearReferenceBeforeSet {
 		option.empty()
 	}
 
 	option.isSet = true
 	option.preventDefault = true
+	option.clearReferenceBeforeSet = false
 
 	if len(option.Choices) != 0 {
 		found := false
@@ -281,6 +283,10 @@ func (option *Option) set(value *string) error {
 }
 
 func (option *Option) setDefault(value *string) error {
+	if option.preventDefault {
+		return nil
+	}
+
 	if err := option.set(value); err != nil {
 		return err
 	}

parser.go

@@ -208,8 +208,7 @@ func (p *Parser) ParseArgs(args []string) ([]string, error) {
 	}
 
 	p.eachOption(func(c *Command, g *Group, option *Option) {
-		option.isSet = false
-		option.isSetDefault = false
+		option.clearReferenceBeforeSet = true
 		option.updateDefaultLiteral()
 	})
 
@@ -713,13 +712,3 @@ func (p *Parser) printError(err error) error {
 
 	return err
 }
-
-func (p *Parser) clearIsSet() {
-	p.eachCommand(func(c *Command) {
-		c.eachGroup(func(g *Group) {
-			for _, option := range g.options {
-				option.isSet = false
-			}
-		})
-	}, true)
-}