You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: prop.go
    path of file: ./repos/gitkube/vendor/cloud.google.com/go/datastore
    
    the code of the file until where you have to start completion: // Copyright 2014 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package datastore

import (
	"fmt"
	"reflect"
	"strings"
	"unicode"

	"cloud.google.com/go/internal/fields"
)

// Entities with more than this many indexed properties will not be saved.
const maxIndexedProperties = 20000

// []byte fields more than 1 megabyte long will not be loaded or saved.
const maxBlobLen = 1 << 20

// Property is a name/value pair plus some metadata. A datastore entity's
// contents are loaded and saved as 
    
func validateChildType(t reflect.Type, fieldName string, flatten, prevSlice bool, prevTypes map[reflect.Type]bool) error {
	if prevTypes[t] {
		return nil
	}
	prevTypes[t] = true

	switch t.Kind() {
	case reflect.Slice:
		if flatten && prevSlice {
			return fmt.Errorf("datastore: flattening nested structs leads to a slice of slices: field %q", fieldName)
		}
		return validateChildType(t.Elem(), fieldName, flatten, true, prevTypes)
	case reflect.Struct:
		if t == typeOfTime || t == typeOfGeoPoint {
			return nil
		}

		for i := 0; i < t.NumField(); i++ {
			f := t.Field(i)

			// If a named field is unexported, ignore it. An anonymous
			// unexported field is processed, because it may contain
			// exported fields, which are visible.
			exported := (f.PkgPath == "")
			if !exported && !f.Anonymous {
				continue
			}

			_, keep, other, err := parseTag(f.Tag)
			// Handle error from parseTag now instead of later (in cache.Fields call).
			if err != nil {
				return err
			}
			if !keep {
				continue
			}
			if other != nil {
				opts := other.(saveOpts)
				flatten = flatten || opts.flatten
			}
			if err := validateChildType(f.Type, f.Name, flatten, prevSlice, prevTypes); err != nil {
				return err
			}
		}
	case reflect.Ptr:
		if t == typeOfKeyPtr {
			return nil
		}
		return validateChildType(t.Elem(), fieldName, flatten, prevSlice, prevTypes)
	}
	return nil
}