fix: Add pointer support for url query params (#3659)

The pointer support in url query params (using []*Struct for binding query params) was previously available in Gin, but was removed in commit 0d50ce8 since there wasn't a test case for such a scenario, and so the case block was removed as a redundant one.

binding/form_mapping.go

@@ -239,6 +239,11 @@ func setWithProperType(val string, value reflect.Value, field reflect.StructFiel
 		return json.Unmarshal(bytesconv.StringToBytes(val), value.Addr().Interface())
 	case reflect.Map:
 		return json.Unmarshal(bytesconv.StringToBytes(val), value.Addr().Interface())
+	case reflect.Ptr:
+		if !value.Elem().IsValid() {
+			value.Set(reflect.New(value.Type().Elem()))
+		}
+		return setWithProperType(val, value.Elem(), field)
 	default:
 		return errUnknownType
 	}

binding/form_mapping_test.go

@@ -269,6 +269,39 @@ func TestMappingStructField(t *testing.T) {
 	assert.Equal(t, 9, s.J.I)
 }
 
+func TestMappingPtrField(t *testing.T) {
+	type ptrStruct struct {
+		Key int64 `json:"key"`
+	}
+
+	type ptrRequest struct {
+		Items []*ptrStruct `json:"items" form:"items"`
+	}
+
+	var err error
+
+	// With 0 items.
+	var req0 ptrRequest
+	err = mappingByPtr(&req0, formSource{}, "form")
+	assert.NoError(t, err)
+	assert.Empty(t, req0.Items)
+
+	// With 1 item.
+	var req1 ptrRequest
+	err = mappingByPtr(&req1, formSource{"items": {`{"key": 1}`}}, "form")
+	assert.NoError(t, err)
+	assert.Len(t, req1.Items, 1)
+	assert.EqualValues(t, 1, req1.Items[0].Key)
+
+	// With 2 items.
+	var req2 ptrRequest
+	err = mappingByPtr(&req2, formSource{"items": {`{"key": 1}`, `{"key": 2}`}}, "form")
+	assert.NoError(t, err)
+	assert.Len(t, req2.Items, 2)
+	assert.EqualValues(t, 1, req2.Items[0].Key)
+	assert.EqualValues(t, 2, req2.Items[1].Key)
+}
+
 func TestMappingMapField(t *testing.T) {
 	var s struct {
 		M map[string]int