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: diff.go
    path of file: ./repos/termdash/private/faketerm
    
    the code of the file until where you have to start completion: // Copyright 2018 Google Inc.
//
// 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 faketerm

// diff.go provides functions that highlight differences between fake terminals.

import (
	"fmt"
	"image"
	"reflect"
	"strings"

	"github.com/kylelemons/godebug/pretty"
	"github.com/mum4k/termdash/cell"
)

// optDiff is used to display differences in cell options.
type optDiff struct {
	// point indicates the cell with the differing options.
	point image.Point

	got  *cell.Options
	want *cell.Options
}

// Diff compares the two terminals, returning an empty string if there is not
// difference. If a difference is found, returns a human readable description
// of the differences.
func Diff(want, got *Terminal) string {
	if reflect.DeepEqual(want.BackBuffer(), got.BackBuffer()) {
		return ""
	}

	var b strings.Builder
	b.WriteString("found differences between the two fake terminals.\n")
	b.WriteString("   got:\n")
	b.WriteString(got.String())
	b.WriteString("  want:\n")
	b.WriteString(want.String())
	b.WriteString(" 
    
func Diff(want, got *Terminal) string {
	if reflect.DeepEqual(want.BackBuffer(), got.BackBuffer()) {
		return ""
	}

	var b strings.Builder
	b.WriteString("found differences between the two fake terminals.\n")
	b.WriteString("   got:\n")
	b.WriteString(got.String())
	b.WriteString("  want:\n")
	b.WriteString(want.String())
	b.WriteString("  diff (unexpected cells highlighted with rune '࿃')\n")
	b.WriteString("  note - this excludes cell options:\n")

	size := got.Size()
	var optDiffs []*optDiff
	cellsDiffer := false
	for row := 0; row < size.Y; row++ {
		for col := 0; col < size.X; col++ {
			p := image.Point{col, row}
			partial, err := got.BackBuffer().IsPartial(p)
			if err != nil {
				panic(fmt.Errorf("unable to determine if point %v is a partial rune: %v", p, err))
			}

			gotCell := got.BackBuffer()[col][row]
			wantCell := want.BackBuffer()[col][row]
			r := gotCell.Rune
			if r != wantCell.Rune {
				r = '࿃'
				cellsDiffer = true
			} else if r == 0 && !partial {
				r = ' '
			}
			b.WriteRune(r)

			if !reflect.DeepEqual(gotCell.Opts, wantCell.Opts) {
				optDiffs = append(optDiffs, &optDiff{
					point: image.Point{col, row},
					got:   gotCell.Opts,
					want:  wantCell.Opts,
				})
			}
		}
		b.WriteRune('\n')
	}

	if len(optDiffs) > 0 {
		b.WriteString("  Found differences in options on some of the cells:\n")
		for _, od := range optDiffs {
			if diff := pretty.Compare(od.want, od.got); diff != "" {
				b.WriteString(fmt.Sprintf("cell %v, diff (-want +got):\n%s\n", od.point, diff))
			}
		}
	}

	if cellsDiffer {
		b.WriteString("  Found differences in some of the cell runes:\n")
		for row := 0; row < size.Y; row++ {
			for col := 0; col < size.X; col++ {
				got := got.BackBuffer()[col][row].Rune
				want := want.BackBuffer()[col][row].Rune
				if got == want {
					continue
				}
				b.WriteString(fmt.Sprintf("  cell(%v, %v) => got '%c' (rune %d), want '%c' (rune %d)\n", col, row, got, got, want, want))
			}
		}
	}
	return b.String()
}