Function WriteContextDiff

internal/difflib/difflib.go:677–760

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 creat

(writer io.Writer, diff ContextDiff)

// 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
	wf := func(format string, args ...interface{}) {
		_, err := buf.WriteString(fmt.Sprintf(format, args...))
		if diffErr == nil && err != nil {
			diffErr = err
		}
	}
	ws := func(s string) {
		_, err := buf.WriteString(s)
		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
			}
			if diff.FromFile != "" || diff.ToFile != "" {
				wf("*** %s%s%s", diff.FromFile, fromDate, diff.Eol)
				wf("--- %s%s%s", diff.ToFile, toDate, diff.Eol)
			}
		}

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

		range1 := formatRangeContext(first.I1, last.I2)
		wf("*** %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
					}