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[bytom/vapor.git] / vendor / github.com / stretchr / testify / vendor / github.com / pmezard / go-difflib / difflib / difflib.go

// Package difflib is a partial port of Python difflib module.
//
// It provides tools to compare sequences of strings and generate textual diffs.
//
// The following class and functions have been ported:
//
// - SequenceMatcher
//
// - unified_diff
//
// - context_diff
//
// Getting unified diffs was the main goal of the port. Keep in mind this code
// is mostly suitable to output text differences in a human friendly way, there
// are no guarantees generated diffs are consumable by patch(1).
package difflib

import (
        "bufio"
        "bytes"
        "fmt"
        "io"
        "strings"
)

func min(a, b int) int {
        if a < b {
                return a
        }
        return b
}

func max(a, b int) int {
        if a > b {
                return a
        }
        return b
}

func calculateRatio(matches, length int) float64 {
        if length > 0 {
                return 2.0 * float64(matches) / float64(length)
        }
        return 1.0
}

type Match struct {
        A    int
        B    int
        Size int
}

type OpCode struct {
        Tag byte
        I1  int
        I2  int
        J1  int
        J2  int
}

// SequenceMatcher compares sequence of strings. The basic
// algorithm predates, and is a little fancier than, an algorithm
// published in the late 1980's by Ratcliff and Obershelp under the
// hyperbolic name "gestalt pattern matching".  The basic idea is to find
// the longest contiguous matching subsequence that contains no "junk"
// elements (R-O doesn't address junk).  The same idea is then applied
// recursively to the pieces of the sequences to the left and to the right
// of the matching subsequence.  This does not yield minimal edit
// sequences, but does tend to yield matches that "look right" to people.
//
// SequenceMatcher tries to compute a "human-friendly diff" between two
// sequences.  Unlike e.g. UNIX(tm) diff, the fundamental notion is the
// longest *contiguous* & junk-free matching subsequence.  That's what
// catches peoples' eyes.  The Windows(tm) windiff has another interesting
// notion, pairing up elements that appear uniquely in each sequence.
// That, and the method here, appear to yield more intuitive difference
// reports than does diff.  This method appears to be the least vulnerable
// to synching up on blocks of "junk lines", though (like blank lines in
// ordinary text files, or maybe "<P>" lines in HTML files).  That may be
// because this is the only method of the 3 that has a *concept* of
// "junk" <wink>.
//
// Timing:  Basic R-O is cubic time worst case and quadratic time expected
// case.  SequenceMatcher is quadratic time for the worst case and has
// expected-case behavior dependent in a complicated way on how many
// elements the sequences have in common; best case time is linear.
type SequenceMatcher struct {
        a              []string
        b              []string
        b2j            map[string][]int
        IsJunk         func(string) bool
        autoJunk       bool
        bJunk          map[string]struct{}
        matchingBlocks []Match
        fullBCount     map[string]int
        bPopular       map[string]struct{}
        opCodes        []OpCode
}

func NewMatcher(a, b []string) *SequenceMatcher {
        m := SequenceMatcher{autoJunk: true}
        m.SetSeqs(a, b)
        return &m
}

func NewMatcherWithJunk(a, b []string, autoJunk bool,
        isJunk func(string) bool) *SequenceMatcher {

        m := SequenceMatcher{IsJunk: isJunk, autoJunk: autoJunk}
        m.SetSeqs(a, b)
        return &m
}

// Set two sequences to be compared.
func (m *SequenceMatcher) SetSeqs(a, b []string) {
        m.SetSeq1(a)
        m.SetSeq2(b)
}

// Set the first sequence to be compared. The second sequence to be compared is
// not changed.
//
// SequenceMatcher computes and caches detailed information about the second
// sequence, so if you want to compare one sequence S against many sequences,
// use .SetSeq2(s) once and call .SetSeq1(x) repeatedly for each of the other
// sequences.
//
// See also SetSeqs() and SetSeq2().
func (m *SequenceMatcher) SetSeq1(a []string) {
        if &a == &m.a {
                return
        }
        m.a = a
        m.matchingBlocks = nil
        m.opCodes = nil
}

// Set the second sequence to be compared. The first sequence to be compared is
// not changed.
func (m *SequenceMatcher) SetSeq2(b []string) {
        if &b == &m.b {
                return
        }
        m.b = b
        m.matchingBlocks = nil
        m.opCodes = nil
        m.fullBCount = nil
        m.chainB()
}

func (m *SequenceMatcher) chainB() {
        // Populate line -> index mapping
        b2j := map[string][]int{}
        for i, s := range m.b {
                indices := b2j[s]
                indices = append(indices, i)
                b2j[s] = indices
        }

        // Purge junk elements
        m.bJunk = map[string]struct{}{}
        if m.IsJunk != nil {
                junk := m.bJunk
                for s, _ := range b2j {
                        if m.IsJunk(s) {
                                junk[s] = struct{}{}
                        }
                }
                for s, _ := range junk {
                        delete(b2j, s)
                }
        }

        // Purge remaining popular elements
        popular := map[string]struct{}{}
        n := len(m.b)
        if m.autoJunk && n >= 200 {
                ntest := n/100 + 1
                for s, indices := range b2j {
                        if len(indices) > ntest {
                                popular[s] = struct{}{}
                        }
                }
                for s, _ := range popular {
                        delete(b2j, s)
                }
        }
        m.bPopular = popular
        m.b2j = b2j
}

func (m *SequenceMatcher) isBJunk(s string) bool {
        _, ok := m.bJunk[s]
        return ok
}

// Find longest matching block in a[alo:ahi] and b[blo:bhi].
//
// If IsJunk is not defined:
//
// Return (i,j,k) such that a[i:i+k] is equal to b[j:j+k], where
//     alo <= i <= i+k <= ahi
//     blo <= j <= j+k <= bhi
// and for all (i',j',k') meeting those conditions,
//     k >= k'
//     i <= i'
//     and if i == i', j <= j'
//
// In other words, of all maximal matching blocks, return one that
// starts earliest in a, and of all those maximal matching blocks that
// start earliest in a, return the one that starts earliest in b.
//
// If IsJunk is defined, first the longest matching block is
// determined as above, but with the additional restriction that no
// junk element appears in the block.  Then that block is extended as
// far as possible by matching (only) junk elements on both sides.  So
// the resulting block never matches on junk except as identical junk
// happens to be adjacent to an "interesting" match.
//
// If no blocks match, return (alo, blo, 0).
func (m *SequenceMatcher) findLongestMatch(alo, ahi, blo, bhi int) Match {
        // CAUTION:  stripping common prefix or suffix would be incorrect.
        // E.g.,
        //    ab
        //    acab
        // Longest matching block is "ab", but if common prefix is
        // stripped, it's "a" (tied with "b").  UNIX(tm) diff does so
        // strip, so ends up claiming that ab is changed to acab by
        // inserting "ca" in the middle.  That's minimal but unintuitive:
        // "it's obvious" that someone inserted "ac" at the front.
        // Windiff ends up at the same place as diff, but by pairing up
        // the unique 'b's and then matching the first two 'a's.
        besti, bestj, bestsize := alo, blo, 0

        // find longest junk-free match
        // during an iteration of the loop, j2len[j] = length of longest
        // junk-free match ending with a[i-1] and b[j]
        j2len := map[int]int{}
        for i := alo; i != ahi; i++ {
                // look at all instances of a[i] in b; note that because
                // b2j has no junk keys, the loop is skipped if a[i] is junk
                newj2len := map[int]int{}
                for _, j := range m.b2j[m.a[i]] {
                        // a[i] matches b[j]
                        if j < blo {
                                continue
                        }
                        if j >= bhi {
                                break
                        }
                        k := j2len[j-1] + 1
                        newj2len[j] = k
                        if k > bestsize {
                                besti, bestj, bestsize = i-k+1, j-k+1, k
                        }
                }
                j2len = newj2len
        }

        // Extend the best by non-junk elements on each end.  In particular,
        // "popular" non-junk elements aren't in b2j, which greatly speeds
        // the inner loop above, but also means "the best" match so far
        // doesn't contain any junk *or* popular non-junk elements.
        for besti > alo && bestj > blo && !m.isBJunk(m.b[bestj-1]) &&
                m.a[besti-1] == m.b[bestj-1] {
                besti, bestj, bestsize = besti-1, bestj-1, bestsize+1
        }
        for besti+bestsize < ahi && bestj+bestsize < bhi &&
                !m.isBJunk(m.b[bestj+bestsize]) &&
                m.a[besti+bestsize] == m.b[bestj+bestsize] {
                bestsize += 1
        }

        // Now that we have a wholly interesting match (albeit possibly
        // empty!), we may as well suck up the matching junk on each
        // side of it too.  Can't think of a good reason not to, and it
        // saves post-processing the (possibly considerable) expense of
        // figuring out what to do with it.  In the case of an empty
        // interesting match, this is clearly the right thing to do,
        // because no other kind of match is possible in the regions.
        for besti > alo && bestj > blo && m.isBJunk(m.b[bestj-1]) &&
                m.a[besti-1] == m.b[bestj-1] {
                besti, bestj, bestsize = besti-1, bestj-1, bestsize+1
        }
        for besti+bestsize < ahi && bestj+bestsize < bhi &&
                m.isBJunk(m.b[bestj+bestsize]) &&
                m.a[besti+bestsize] == m.b[bestj+bestsize] {
                bestsize += 1
        }

        return Match{A: besti, B: bestj, Size: bestsize}
}

// Return list of triples describing matching subsequences.
//
// Each triple is of the form (i, j, n), and means that
// a[i:i+n] == b[j:j+n].  The triples are monotonically increasing in
// i and in j. It's also guaranteed that if (i, j, n) and (i', j', n') are
// adjacent triples in the list, and the second is not the last triple in the
// list, then i+n != i' or j+n != j'. IOW, adjacent triples never describe
// adjacent equal blocks.
//
// The last triple is a dummy, (len(a), len(b), 0), and is the only
// triple with n==0.
func (m *SequenceMatcher) GetMatchingBlocks() []Match {
        if m.matchingBlocks != nil {
                return m.matchingBlocks
        }

        var matchBlocks func(alo, ahi, blo, bhi int, matched []Match) []Match
        matchBlocks = func(alo, ahi, blo, bhi int, matched []Match) []Match {
                match := m.findLongestMatch(alo, ahi, blo, bhi)
                i, j, k := match.A, match.B, match.Size
                if match.Size > 0 {
                        if alo < i && blo < j {
                                matched = matchBlocks(alo, i, blo, j, matched)
                        }
                        matched = append(matched, match)
                        if i+k < ahi && j+k < bhi {
                                matched = matchBlocks(i+k, ahi, j+k, bhi, matched)
                        }
                }
                return matched
        }
        matched := matchBlocks(0, len(m.a), 0, len(m.b), nil)

        // It's possible that we have adjacent equal blocks in the
        // matching_blocks list now.
        nonAdjacent := []Match{}
        i1, j1, k1 := 0, 0, 0
        for _, b := range matched {
                // Is this block adjacent to i1, j1, k1?
                i2, j2, k2 := b.A, b.B, b.Size
                if i1+k1 == i2 && j1+k1 == j2 {
                        // Yes, so collapse them -- this just increases the length of
                        // the first block by the length of the second, and the first
                        // block so lengthened remains the block to compare against.
                        k1 += k2
                } else {
                        // Not adjacent.  Remember the first block (k1==0 means it's
                        // the dummy we started with), and make the second block the
                        // new block to compare against.
                        if k1 > 0 {
                                nonAdjacent = append(nonAdjacent, Match{i1, j1, k1})
                        }
                        i1, j1, k1 = i2, j2, k2
                }
        }
        if k1 > 0 {
                nonAdjacent = append(nonAdjacent, Match{i1, j1, k1})
        }

        nonAdjacent = append(nonAdjacent, Match{len(m.a), len(m.b), 0})
        m.matchingBlocks = nonAdjacent
        return m.matchingBlocks
}

// Return list of 5-tuples describing how to turn a into b.
//
// Each tuple is of the form (tag, i1, i2, j1, j2).  The first tuple
// has i1 == j1 == 0, and remaining tuples have i1 == the i2 from the
// tuple preceding it, and likewise for j1 == the previous j2.
//
// The tags are characters, with these meanings:
//
// 'r' (replace):  a[i1:i2] should be replaced by b[j1:j2]
//
// 'd' (delete):   a[i1:i2] should be deleted, j1==j2 in this case.
//
// 'i' (insert):   b[j1:j2] should be inserted at a[i1:i1], i1==i2 in this case.
//
// 'e' (equal):    a[i1:i2] == b[j1:j2]
func (m *SequenceMatcher) GetOpCodes() []OpCode {
        if m.opCodes != nil {
                return m.opCodes
        }
        i, j := 0, 0
        matching := m.GetMatchingBlocks()
        opCodes := make([]OpCode, 0, len(matching))
        for _, m := range matching {
                //  invariant:  we've pumped out correct diffs to change
                //  a[:i] into b[:j], and the next matching block is
                //  a[ai:ai+size] == b[bj:bj+size]. So we need to pump
                //  out a diff to change a[i:ai] into b[j:bj], pump out
                //  the matching block, and move (i,j) beyond the match
                ai, bj, size := m.A, m.B, m.Size
                tag := byte(0)
                if i < ai && j < bj {
                        tag = 'r'
                } else if i < ai {
                        tag = 'd'
                } else if j < bj {
                        tag = 'i'
                }
                if tag > 0 {
                        opCodes = append(opCodes, OpCode{tag, i, ai, j, bj})
                }
                i, j = ai+size, bj+size
                // the list of matching blocks is terminated by a
                // sentinel with size 0
                if size > 0 {
                        opCodes = append(opCodes, OpCode{'e', ai, i, bj, j})
                }
        }
        m.opCodes = opCodes
        return m.opCodes
}

// Isolate change clusters by eliminating ranges with no changes.
//
// Return a generator of groups with up to n lines of context.
// Each group is in the same format as returned by GetOpCodes().
func (m *SequenceMatcher) GetGroupedOpCodes(n int) [][]OpCode {
        if n < 0 {
                n = 3
        }
        codes := m.GetOpCodes()
        if len(codes) == 0 {
                codes = []OpCode{OpCode{'e', 0, 1, 0, 1}}
        }
        // Fixup leading and trailing groups if they show no changes.
        if codes[0].Tag == 'e' {
                c := codes[0]
                i1, i2, j1, j2 := c.I1, c.I2, c.J1, c.J2
                codes[0] = OpCode{c.Tag, max(i1, i2-n), i2, max(j1, j2-n), j2}
        }
        if codes[len(codes)-1].Tag == 'e' {
                c := codes[len(codes)-1]
                i1, i2, j1, j2 := c.I1, c.I2, c.J1, c.J2
                codes[len(codes)-1] = OpCode{c.Tag, i1, min(i2, i1+n), j1, min(j2, j1+n)}
        }
        nn := n + n
        groups := [][]OpCode{}
        group := []OpCode{}
        for _, c := range codes {
                i1, i2, j1, j2 := c.I1, c.I2, c.J1, c.J2
                // End the current group and start a new one whenever
                // there is a large range with no changes.
                if c.Tag == 'e' && i2-i1 > nn {
                        group = append(group, OpCode{c.Tag, i1, min(i2, i1+n),
                                j1, min(j2, j1+n)})
                        groups = append(groups, group)
                        group = []OpCode{}
                        i1, j1 = max(i1, i2-n), max(j1, j2-n)
                }
                group = append(group, OpCode{c.Tag, i1, i2, j1, j2})
        }
        if len(group) > 0 && !(len(group) == 1 && group[0].Tag == 'e') {
                groups = append(groups, group)
        }
        return groups
}

// Return a measure of the sequences' similarity (float in [0,1]).
//
// Where T is the total number of elements in both sequences, and
// M is the number of matches, this is 2.0*M / T.
// Note that this is 1 if the sequences are identical, and 0 if
// they have nothing in common.
//
// .Ratio() is expensive to compute if you haven't already computed
// .GetMatchingBlocks() or .GetOpCodes(), in which case you may
// want to try .QuickRatio() or .RealQuickRation() first to get an
// upper bound.
func (m *SequenceMatcher) Ratio() float64 {
        matches := 0
        for _, m := range m.GetMatchingBlocks() {
                matches += m.Size
        }
        return calculateRatio(matches, len(m.a)+len(m.b))
}

// Return an upper bound on ratio() relatively quickly.
//
// This isn't defined beyond that it is an upper bound on .Ratio(), and
// is faster to compute.
func (m *SequenceMatcher) QuickRatio() float64 {
        // viewing a and b as multisets, set matches to the cardinality
        // of their intersection; this counts the number of matches
        // without regard to order, so is clearly an upper bound
        if m.fullBCount == nil {
                m.fullBCount = map[string]int{}
                for _, s := range m.b {
                        m.fullBCount[s] = m.fullBCount[s] + 1
                }
        }

        // avail[x] is the number of times x appears in 'b' less the
        // number of times we've seen it in 'a' so far ... kinda
        avail := map[string]int{}
        matches := 0
        for _, s := range m.a {
                n, ok := avail[s]
                if !ok {
                        n = m.fullBCount[s]
                }
                avail[s] = n - 1
                if n > 0 {
                        matches += 1
                }
        }
        return calculateRatio(matches, len(m.a)+len(m.b))
}

// Return an upper bound on ratio() very quickly.
//
// This isn't defined beyond that it is an upper bound on .Ratio(), and
// is faster to compute than either .Ratio() or .QuickRatio().
func (m *SequenceMatcher) RealQuickRatio() float64 {
        la, lb := len(m.a), len(m.b)
        return calculateRatio(min(la, lb), la+lb)
}

// Convert range to the "ed" format
func formatRangeUnified(start, stop int) string {
        // Per the diff spec at http://www.unix.org/single_unix_specification/
        beginning := start + 1 // lines start numbering with one
        length := stop - start
        if length == 1 {
                return fmt.Sprintf("%d", beginning)
        }
        if length == 0 {
                beginning -= 1 // empty ranges begin at line just before the range
        }
        return fmt.Sprintf("%d,%d", beginning, length)
}

// Unified diff parameters
type UnifiedDiff struct {
        A        []string // First sequence lines
        FromFile string   // First file name
        FromDate string   // First file time
        B        []string // Second sequence lines
        ToFile   string   // Second file name
        ToDate   string   // Second file time
        Eol      string   // Headers end of line, defaults to LF
        Context  int      // Number of context lines
}

// Compare two sequences of lines; generate the delta as a unified diff.
//
// Unified diffs are a compact way of showing line changes and a few
// lines of context.  The number of context lines is set by 'n' which
// defaults to three.
//
// By default, the diff control lines (those with ---, +++, or @@) are
// created with a trailing newline.  This is helpful so that inputs
// created from file.readlines() result in diffs that are suitable for
// file.writelines() since both the inputs and outputs have trailing
// newlines.
//
// For inputs that do not have trailing newlines, set the lineterm
// argument to "" so that the output will be uniformly newline free.
//
// The unidiff format normally has a header for filenames and modification
// times.  Any or all of these may be specified using strings for
// 'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.
// The modification times are normally expressed in the ISO 8601 format.
func WriteUnifiedDiff(writer io.Writer, diff UnifiedDiff) error {
        buf := bufio.NewWriter(writer)
        defer buf.Flush()
        w := func(format string, args ...interface{}) error {
                _, err := buf.WriteString(fmt.Sprintf(format, args...))
                return err
        }

        if len(diff.Eol) == 0 {
                diff.Eol = "\n"
        }

        started := false
        m := NewMatcher(diff.A, diff.B)
        for _, g := range m.GetGroupedOpCodes(diff.Context) {
                if !started {
                        started = true
                        fromDate := ""
                        if len(diff.FromDate) > 0 {
                                fromDate = "\t" + diff.FromDate
                        }
                        toDate := ""
                        if len(diff.ToDate) > 0 {
                                toDate = "\t" + diff.ToDate
                        }
                        err := w("--- %s%s%s", diff.FromFile, fromDate, diff.Eol)
                        if err != nil {
                                return err
                        }
                        err = w("+++ %s%s%s", diff.ToFile, toDate, diff.Eol)
                        if err != nil {
                                return err
                        }
                }
                first, last := g[0], g[len(g)-1]
                range1 := formatRangeUnified(first.I1, last.I2)
                range2 := formatRangeUnified(first.J1, last.J2)
                if err := w("@@ -%s +%s @@%s", range1, range2, diff.Eol); err != nil {
                        return err
                }
                for _, c := range g {
                        i1, i2, j1, j2 := c.I1, c.I2, c.J1, c.J2
                        if c.Tag == 'e' {
                                for _, line := range diff.A[i1:i2] {
                                        if err := w(" " + line); err != nil {
                                                return err
                                        }
                                }
                                continue
                        }
                        if c.Tag == 'r' || c.Tag == 'd' {
                                for _, line := range diff.A[i1:i2] {
                                        if err := w("-" + line); err != nil {
                                                return err
                                        }
                                }
                        }
                        if c.Tag == 'r' || c.Tag == 'i' {
                                for _, line := range diff.B[j1:j2] {
                                        if err := w("+" + line); err != nil {
                                                return err
                                        }
                                }
                        }
                }
        }
        return nil
}

// Like WriteUnifiedDiff but returns the diff a string.
func GetUnifiedDiffString(diff UnifiedDiff) (string, error) {
        w := &bytes.Buffer{}
        err := WriteUnifiedDiff(w, diff)
        return string(w.Bytes()), err
}

// Convert range to the "ed" format.
func formatRangeContext(start, stop int) string {
        // Per the diff spec at http://www.unix.org/single_unix_specification/
        beginning := start + 1 // lines start numbering with one
        length := stop - start
        if length == 0 {
                beginning -= 1 // empty ranges begin at line just before the range
        }
        if length <= 1 {
                return fmt.Sprintf("%d", beginning)
        }
        return fmt.Sprintf("%d,%d", beginning, beginning+length-1)
}

type ContextDiff UnifiedDiff

// Compare two sequences of lines; generate the delta as a context diff.
//
// Context diffs are a compact way of showing line changes and a few
// lines of context. The number of context lines is set by diff.Context
// which defaults to three.
//
// By default, the diff control lines (those with *** or ---) are
// created with a trailing newline.
//
// For inputs that do not have trailing newlines, set the diff.Eol
// argument to "" so that the output will be uniformly newline free.
//
// The context diff format normally has a header for filenames and
// modification times.  Any or all of these may be specified using
// strings for diff.FromFile, diff.ToFile, diff.FromDate, diff.ToDate.
// The modification times are normally expressed in the ISO 8601 format.
// If not specified, the strings default to blanks.
func WriteContextDiff(writer io.Writer, diff ContextDiff) error {
        buf := bufio.NewWriter(writer)
        defer buf.Flush()
        var diffErr error
        w := func(format string, args ...interface{}) {
                _, err := buf.WriteString(fmt.Sprintf(format, args...))
                if diffErr == nil && err != nil {
                        diffErr = err
                }
        }

        if len(diff.Eol) == 0 {
                diff.Eol = "\n"
        }

        prefix := map[byte]string{
                'i': "+ ",
                'd': "- ",
                'r': "! ",
                'e': "  ",
        }

        started := false
        m := NewMatcher(diff.A, diff.B)
        for _, g := range m.GetGroupedOpCodes(diff.Context) {
                if !started {
                        started = true
                        fromDate := ""
                        if len(diff.FromDate) > 0 {
                                fromDate = "\t" + diff.FromDate
                        }
                        toDate := ""
                        if len(diff.ToDate) > 0 {
                                toDate = "\t" + diff.ToDate
                        }
                        w("*** %s%s%s", diff.FromFile, fromDate, diff.Eol)
                        w("--- %s%s%s", diff.ToFile, toDate, diff.Eol)
                }

                first, last := g[0], g[len(g)-1]
                w("***************" + diff.Eol)

                range1 := formatRangeContext(first.I1, last.I2)
                w("*** %s ****%s", range1, diff.Eol)
                for _, c := range g {
                        if c.Tag == 'r' || c.Tag == 'd' {
                                for _, cc := range g {
                                        if cc.Tag == 'i' {
                                                continue
                                        }
                                        for _, line := range diff.A[cc.I1:cc.I2] {
                                                w(prefix[cc.Tag] + line)
                                        }
                                }
                                break
                        }
                }

                range2 := formatRangeContext(first.J1, last.J2)
                w("--- %s ----%s", range2, diff.Eol)
                for _, c := range g {
                        if c.Tag == 'r' || c.Tag == 'i' {
                                for _, cc := range g {
                                        if cc.Tag == 'd' {
                                                continue
                                        }
                                        for _, line := range diff.B[cc.J1:cc.J2] {
                                                w(prefix[cc.Tag] + line)
                                        }
                                }
                                break
                        }
                }
        }
        return diffErr
}

// Like WriteContextDiff but returns the diff a string.
func GetContextDiffString(diff ContextDiff) (string, error) {
        w := &bytes.Buffer{}
        err := WriteContextDiff(w, diff)
        return string(w.Bytes()), err
}

// Split a string on "\n" while preserving them. The output can be used
// as input for UnifiedDiff and ContextDiff structures.
func SplitLines(s string) []string {
        lines := strings.SplitAfter(s, "\n")
        lines[len(lines)-1] += "\n"
        return lines
}