fix: indirection through nil pointer to embedded struct (#211)

The provided test `TestUnmarshallToEmbeddedNoData` shows that the
decoder panics when `setDefaults` encounters a nil pointer to an
embedded struct. The fix replaces `FieldByName` with `FieldByIndexErr`
to catch this kind of situation and continue with the next field.

Author: morus12

decoder.go

@@ -104,6 +104,15 @@ func (d *Decoder) setDefaults(t reflect.Type, v reflect.Value) MultiError {
 
 	errs := MultiError{}
 
+	if v.Type().Kind() == reflect.Struct {
+		for i := 0; i < v.NumField(); i++ {
+			field := v.Field(i)
+			if field.Type().Kind() == reflect.Ptr && field.IsNil() && v.Type().Field(i).Anonymous {
+				field.Set(reflect.New(field.Type().Elem()))
+			}
+		}
+	}
+
 	for _, f := range struc.fields {
 		vCurrent := v.FieldByName(f.name)
 
@@ -121,15 +130,15 @@ func (d *Decoder) setDefaults(t reflect.Type, v reflect.Value) MultiError {
 			} else if f.typ.Kind() == reflect.Slice {
 				vals := strings.Split(f.defaultValue, "|")
 
-				//check if slice has one of the supported types for defaults
+				// check if slice has one of the supported types for defaults
 				if _, ok := builtinConverters[f.typ.Elem().Kind()]; !ok {
 					errs.merge(MultiError{"default-" + f.name: errors.New("default option is supported only on: bool, float variants, string, unit variants types or their corresponding pointers or slices")})
 					continue
 				}
 
 				defaultSlice := reflect.MakeSlice(f.typ, 0, cap(vals))
 				for _, val := range vals {
-					//this check is to handle if the wrong value is provided
+					// this check is to handle if the wrong value is provided
 					convertedVal := builtinConverters[f.typ.Elem().Kind()](val)
 					if !convertedVal.IsValid() {
 						errs.merge(MultiError{"default-" + f.name: fmt.Errorf("failed setting default: %s is not compatible with field %s type", val, f.name)})
@@ -145,12 +154,12 @@ func (d *Decoder) setDefaults(t reflect.Type, v reflect.Value) MultiError {
 					errs.merge(MultiError{"default-" + f.name: errors.New("default option is supported only on: bool, float variants, string, unit variants types or their corresponding pointers or slices")})
 				}
 
-				//this check is to handle if the wrong value is provided
+				// this check is to handle if the wrong value is provided
 				if convertedVal := convertPointer(t1.Kind(), f.defaultValue); convertedVal.IsValid() {
 					vCurrent.Set(convertedVal)
 				}
 			} else {
-				//this check is to handle if the wrong value is provided
+				// this check is to handle if the wrong value is provided
 				if convertedVal := builtinConverters[f.typ.Kind()](f.defaultValue); convertedVal.IsValid() {
 					vCurrent.Set(builtinConverters[f.typ.Kind()](f.defaultValue))
 				}

decoder_test.go

@@ -2057,6 +2057,74 @@ func TestUnmashalPointerToEmbedded(t *testing.T) {
 	}
 }
 
+type S24 struct {
+	F1 string `schema:"F1"`
+}
+
+type S24e struct {
+	*S24
+	F2 string `schema:"F2"`	
+}
+
+func TestUnmarshallToEmbeddedNoData(t *testing.T) {
+	data := map[string][]string{
+		"F3": {"raw a"},
+	}
+
+	s := &S24e{}
+
+	decoder := NewDecoder()
+	err := decoder.Decode(s, data);
+	
+	expectedErr := `schema: invalid path "F3"`
+	if err.Error() != expectedErr {
+		t.Fatalf("got %q, want %q", err, expectedErr)
+	}
+}
+type S25ee struct {
+	F3 string `schema:"F3"`
+}
+
+type S25e struct {
+	S25ee
+	F2 string `schema:"F2"`
+}
+
+type S25 struct {
+	S25e
+	F1 string `schema:"F1"`
+}
+
+func TestDoubleEmbedded(t *testing.T){
+	data := map[string][]string{
+		"F1": {"raw a"},
+		"F2": {"raw b"},
+		"F3": {"raw c"},
+	}
+
+	
+	s := S25{}
+	decoder := NewDecoder()
+
+	if err := decoder.Decode(&s, data); err != nil {
+		t.Fatal("Error while decoding:", err)
+	}
+
+	expected := S25{
+		F1: "raw a",
+		S25e: S25e{
+			F2: "raw b",
+			S25ee: S25ee{
+				F3: "raw c",
+			},
+		},
+	}
+	if !reflect.DeepEqual(expected, s) {
+		t.Errorf("Expected %v errors, got %v", expected, s)
+	}
+
+}
+
 func TestDefaultValuesAreSet(t *testing.T) {
 	type N struct {
 		S1 string    `schema:"s1,default:test1"`