Standardize on int64 for line numbers

This matches the type used for positions in text fragments.

gitdiff/apply.go

···
 // the line at limit and the line number. If the error is nil or io.EOF, the
 // line number equals limit. A negative limit checks that the source has no
 // more lines to read.
-func copyLines(dst io.Writer, src LineReader, limit int64) (string, int, error) {
-	// TODO(bkeyes): fix int vs int64 for limit and return value
+func copyLines(dst io.Writer, src LineReader, limit int64) (string, int64, error) {
 	for {
 		line, n, err := src.ReadLine()
 		switch {
 		case limit < 0 && err == io.EOF && line == "":
-			return "", int(limit), nil
-		case int64(n) == limit:
+			return "", limit, nil
+		case n == limit:
 			return line, n, err
-		case int64(n) > limit:
+		case n > limit:
 			if limit < 0 {
 				return "", n, conflictError("cannot create new file from non-empty src")
 			}

gitdiff/io.go

···
 // numbers may be incorrect if calls to ReadLine are mixed with calls to other
 // read methods.
 type LineReader interface {
-	// TODO(bkeyes): consider making lineno int64 to match fragment types
-	ReadLine() (string, int, error)
+	ReadLine() (string, int64, error)
 }
 
 // NewLineReader returns a LineReader starting at a specific line and using the
 // newline character, \n, as a line separator. If r is a StringReader, it is
 // used directly. Otherwise, it is wrapped in a way that may read extra data
 // from the underlying input.
-func NewLineReader(r io.Reader, lineno int) LineReader {
+func NewLineReader(r io.Reader, lineno int64) LineReader {
 	sr, ok := r.(readStringReader)
 	if !ok {
 		sr = bufio.NewReader(r)
···
 
 type lineReader struct {
 	r readStringReader
-	n int
+	n int64
 }
 
-func (lr *lineReader) ReadLine() (line string, lineno int, err error) {
+func (lr *lineReader) ReadLine() (line string, lineno int64, err error) {
 	lineno = lr.n
 	line, err = lr.r.ReadString('\n')
 	if err == nil {

gitdiff/io_test.go

···
 			if d != line.Data {
 				t.Errorf("incorrect line data: expected %q, actual %q", line.Data, d)
 			}
-			if n != i {
+			if n != int64(i) {
 				t.Errorf("incorrect line number: expected %d, actual %d", i, n)
 			}
 		}