feat: allow explicitly set path with default to an empty string to clear it (#592)

Author: mitar

mapper.go

@@ -584,6 +584,7 @@ func pathMapper(r *Registry) MapperFunc {
 		if target.Kind() == reflect.Slice {
 			return sliceDecoder(r)(ctx, target)
 		}
+		originalTarget := target
 		if target.Kind() == reflect.Ptr && target.Elem().Kind() == reflect.String {
 			if target.IsNil() {
 				return nil
@@ -598,6 +599,13 @@ func pathMapper(r *Registry) MapperFunc {
 		if err != nil {
 			return err
 		}
+		// Skip if path with default is explicitly set to "". For the current directory use ".".
+		if ctx.Value.HasDefault && path == "" {
+			if originalTarget.Kind() == reflect.Ptr {
+				originalTarget.Set(reflect.Zero(originalTarget.Type()))
+			}
+			return nil
+		}
 		if path != "-" {
 			path = ExpandPath(path)
 		}

mapper_test.go

@@ -555,6 +555,42 @@ func TestPathMapperUsingStringPointer(t *testing.T) {
 	})
 }
 
+func TestPathMapperWithDefaultUsingStringPointer(t *testing.T) {
+	type CLI struct {
+		Path *string `type:"path" default:"foobar"`
+	}
+	var cli CLI
+
+	t.Run("With value", func(t *testing.T) {
+		pwd, err := os.Getwd()
+		assert.NoError(t, err)
+		p := mustNew(t, &cli)
+		_, err = p.Parse([]string{"--path", "."})
+		assert.NoError(t, err)
+		assert.NotZero(t, cli.Path)
+		assert.Equal(t, pwd, *cli.Path)
+	})
+
+	t.Run("Zero value", func(t *testing.T) {
+		p := mustNew(t, &cli)
+		_, err := p.Parse([]string{"--path", ""})
+		assert.NoError(t, err)
+		assert.Equal(t, nil, cli.Path)
+	})
+
+	t.Run("Without value", func(t *testing.T) {
+		pwd, err := os.Getwd()
+		assert.NoError(t, err)
+		pwd = filepath.Join(pwd, "foobar")
+		pwd, err = filepath.Abs(pwd)
+		assert.NoError(t, err)
+		p := mustNew(t, &cli)
+		_, err = p.Parse([]string{"--"})
+		assert.NoError(t, err)
+		assert.Equal(t, pwd, *cli.Path)
+	})
+}
+
 //nolint:dupl
 func TestExistingFileMapper(t *testing.T) {
 	type CLI struct {