Treat out-of-range slice indexes in struct paths as missing

CHANGELOG.md

@@ -5,6 +5,7 @@
 - Resolve string and integer map keys using their declared type during nested
   struct validation and filter/default write-back, including defined key types.
   Invalid or overflowing integer path segments are treated as missing entries.
+- Treat out-of-range slice and array indexes in struct field paths as missing instead of panicking.
 
 ## v2.0.0
 

data_source.go

@@ -426,6 +426,9 @@ func (d *StructData) tryGetRV(field string) (fv reflect.Value, exist, zero bool)
 			switch kind {
 			case reflect.Array, reflect.Slice:
 				index, _ := strconv.Atoi(fieldNode)
+				if index < 0 || index >= fv.Len() {
+					return reflect.Value{}, false, false
+				}
 				fv = fv.Index(index)
 			case reflect.Map:
 				fv = structMapValue(fv, fieldNode)
@@ -614,6 +617,9 @@ func (d *StructData) Set(field string, val any) (newVal any, err error) {
 					if err != nil {
 						return nil, ErrInvalidData
 					}
+					if index >= fv.Len() {
+						return nil, ErrNoField
+					}
 
 					fv = fv.Index(index)
 				case reflect.Map:

data_source_test.go

@@ -261,6 +261,52 @@ func TestStructData_Get_ptrVal(t *testing.T) {
 	assert.Equal(t, 0, *val.(*int))
 }
 
+func TestStructData_sliceIndexOutOfRange(t *testing.T) {
+	type Item struct {
+		Name string
+	}
+	form := &struct {
+		Items []Item
+		Fixed [1]Item
+	}{Items: []Item{{Name: "Ada"}}, Fixed: [1]Item{{Name: "Ada"}}}
+
+	d, err := FromStruct(form)
+	assert.NoErr(t, err)
+	for _, path := range []string{"Items.0.Name", "Fixed.0.Name"} {
+		value, exist, zero := d.TryGet(path)
+		assert.True(t, exist)
+		assert.False(t, zero)
+		assert.Eq(t, "Ada", value)
+	}
+	for _, path := range []string{"Items.1.Name", "Items.-1.Name", "Fixed.1.Name"} {
+		value, exist, zero := d.TryGet(path)
+		assert.False(t, exist)
+		assert.False(t, zero)
+		assert.Nil(t, value)
+	}
+
+	// a resolved index that no longer exists when written back
+	d, err = FromStruct(form)
+	assert.NoErr(t, err)
+	_, exist := d.Get("Items.0.Name")
+	assert.True(t, exist)
+	form.Items = nil
+	_, err = d.Set("Items.0.Name", "Grace")
+	assert.Eq(t, ErrNoField, err)
+
+	v := Struct(&struct{ Items []Item }{})
+	v.StringRule("Items.0.Name", "required")
+	assert.False(t, v.Validate())
+	assert.NotEmpty(t, v.Errors.Field("Items.0.Name"))
+
+	type Order struct {
+		Items []Item
+		Kind  string `validate:"requiredIf:Items.0.Name,gift"`
+	}
+	assert.True(t, Struct(&Order{}).Validate())
+	assert.False(t, Struct(&Order{Items: []Item{{Name: "gift"}}}).Validate())
+}
+
 func TestValidatePrivateFieldsWhenTrue(t *testing.T) {
 	type foo struct {
 		Field1 int `validate:"required|min:5|max:20" message:"Field1 outside of range"`