From d905a35c2108c13ac240ffb4e3b7c5f0c2343b46 Mon Sep 17 00:00:00 2001
From: Michelle Laurenti <asmeikal@me.com>
Date: Wed, 23 Jul 2025 12:02:14 +0200
Subject: [PATCH] feat(form): support BindUnmarshaler slice elements

gin-gonic#4312
---
 binding/form_mapping.go      | 16 +++++++++++-
 binding/form_mapping_test.go | 48 ++++++++++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/binding/form_mapping.go b/binding/form_mapping.go
index 45a39e15..d6944955 100644
--- a/binding/form_mapping.go
+++ b/binding/form_mapping.go
@@ -183,8 +183,15 @@ type BindUnmarshaler interface {
 // If the value implements the BindUnmarshaler interface, it will be used to set the value, we will return `true`
 // to skip the default value setting.
 func trySetCustom(val string, value reflect.Value) (isSet bool, err error) {
-	switch v := value.Addr().Interface().(type) {
+	if value.Kind() != reflect.Ptr {
+		value = value.Addr()
+	}
+	switch value.Interface().(type) {
 	case BindUnmarshaler:
+		if !value.Elem().IsValid() {
+			value.Set(reflect.New(value.Type().Elem()))
+		}
+		v := value.Interface().(BindUnmarshaler)
 		return true, v.UnmarshalParam(val)
 	}
 	return false, nil
@@ -449,6 +456,13 @@ func setTimeField(val string, structField reflect.StructField, value reflect.Val
 
 func setArray(vals []string, value reflect.Value, field reflect.StructField) error {
 	for i, s := range vals {
+		if ok, err := trySetCustom(s, value.Index(i)); ok {
+			if err != nil {
+				return err
+			} else {
+				continue
+			}
+		}
 		err := setWithProperType(s, value.Index(i), field)
 		if err != nil {
 			return err
diff --git a/binding/form_mapping_test.go b/binding/form_mapping_test.go
index 55b967a3..0acb53d2 100644
--- a/binding/form_mapping_test.go
+++ b/binding/form_mapping_test.go
@@ -550,6 +550,54 @@ func TestMappingCustomPointerStructTypeWithURITag(t *testing.T) {
 	assert.Equal(t, "happiness", s.FileData.Name)
 }
 
+func TestMappingCustomStructTypeSliceWithFormTag(t *testing.T) {
+	var s struct {
+		FileData []customUnmarshalParamType `form:"data"`
+	}
+	err := mappingByPtr(&s, formSource{"data": {`file:/foo:happiness`, `http:/bar:sadness`}}, "form")
+	require.NoError(t, err)
+
+	assert.Equal(t, "file", s.FileData[0].Protocol)
+	assert.Equal(t, "/foo", s.FileData[0].Path)
+	assert.Equal(t, "happiness", s.FileData[0].Name)
+
+	assert.Equal(t, "http", s.FileData[1].Protocol)
+	assert.Equal(t, "/bar", s.FileData[1].Path)
+	assert.Equal(t, "sadness", s.FileData[1].Name)
+}
+
+func TestMappingCustomStructTypeSliceWithURITag(t *testing.T) {
+	var s struct {
+		FileData []customUnmarshalParamType `uri:"data"`
+	}
+	err := mappingByPtr(&s, formSource{"data": {`file:/foo:happiness`, `http:/bar:sadness`}}, "uri")
+	require.NoError(t, err)
+
+	assert.Equal(t, "file", s.FileData[0].Protocol)
+	assert.Equal(t, "/foo", s.FileData[0].Path)
+	assert.Equal(t, "happiness", s.FileData[0].Name)
+
+	assert.Equal(t, "http", s.FileData[1].Protocol)
+	assert.Equal(t, "/bar", s.FileData[1].Path)
+	assert.Equal(t, "sadness", s.FileData[1].Name)
+}
+
+func TestMappingCustomPointerStructTypeSliceWithFormTag(t *testing.T) {
+	var s struct {
+		FileData []*customUnmarshalParamType `form:"data"`
+	}
+	err := mappingByPtr(&s, formSource{"data": {`file:/foo:happiness`, `http:/bar:sadness`}}, "form")
+	require.NoError(t, err)
+
+	assert.Equal(t, "file", s.FileData[0].Protocol)
+	assert.Equal(t, "/foo", s.FileData[0].Path)
+	assert.Equal(t, "happiness", s.FileData[0].Name)
+
+	assert.Equal(t, "http", s.FileData[1].Protocol)
+	assert.Equal(t, "/bar", s.FileData[1].Path)
+	assert.Equal(t, "sadness", s.FileData[1].Name)
+}
+
 type customPath []string
 
 func (p *customPath) UnmarshalParam(param string) error {