fix: driver.Valuer returns itself causes stackoverflow

Fixes: #657

internal/dbtest/db_test.go

@@ -275,6 +275,8 @@ func TestDB(t *testing.T) {
 		{testJSONMarshaler},
 		{testNilDriverValue},
 		{testRunInTxAndSavepoint},
+		{testEmbedTypeField},
+		{testDriverValuerReturnsItself},
 	}
 
 	testEachDB(t, func(t *testing.T, dbName string, db *bun.DB) {
@@ -1641,3 +1643,31 @@ func testRunInTxAndSavepoint(t *testing.T, db *bun.DB) {
 	require.NoError(t, err)
 	require.Equal(t, 4, count)
 }
+
+type anotherString string
+
+var (
+	_ driver.Valuer = (*anotherString)(nil)
+)
+
+func (v anotherString) Value() (driver.Value, error) {
+	return v, nil
+}
+
+func testDriverValuerReturnsItself(t *testing.T, db *bun.DB) {
+	var expectedValue = anotherString("example value")
+
+	type Model struct {
+		ID    int           `bun:",pk,autoincrement"`
+		Value anotherString `bun:"value"`
+	}
+
+	ctx := context.Background()
+
+	err := db.ResetModel(ctx, (*Model)(nil))
+	require.NoError(t, err)
+
+	model := &Model{Value: expectedValue}
+	_, err = db.NewInsert().Model(model).Exec(ctx)
+	require.Error(t, err)
+}

schema/append_value.go

@@ -274,6 +274,9 @@ func appendDriverValue(fmter Formatter, b []byte, v reflect.Value) []byte {
 	if err != nil {
 		return dialect.AppendError(b, err)
 	}
+	if _, ok := value.(driver.Valuer); ok {
+		return dialect.AppendError(b, fmt.Errorf("driver.Valuer returns unsupported type %T", value))
+	}
 	return Append(fmter, b, value)
 }