From 88dad17ee3c80dded864ddf4692e5fd327bf3bc7 Mon Sep 17 00:00:00 2001
From: Brandon Dyck <brandon@dyck.us>
Date: Wed, 11 Sep 2024 14:23:08 -0600
Subject: [PATCH] Handle reader errors in Regexp

---
 bytes/regexp.go | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/bytes/regexp.go b/bytes/regexp.go
index c7c3272..7b0b7c1 100644
--- a/bytes/regexp.go
+++ b/bytes/regexp.go
@@ -16,6 +16,7 @@ import (
 // with the regexp package.
 type RuneReader struct {
 	cursor cursor.Cursor[byte]
+	err    error
 }
 
 func NewRuneReader(c cursor.Cursor[byte]) *RuneReader {
@@ -23,6 +24,9 @@ func NewRuneReader(c cursor.Cursor[byte]) *RuneReader {
 }
 
 func (rr *RuneReader) ReadRune() (r rune, size int, err error) {
+	defer func() {
+		rr.err = err
+	}()
 	var b [4]byte
 	s := b[:]
 	n, next, err := rr.cursor.Read(s)
@@ -40,6 +44,10 @@ func (rr *RuneReader) Cursor() cursor.Cursor[byte] {
 	return rr.cursor
 }
 
+func (rr *RuneReader) Error() error {
+	return rr.err
+}
+
 func Regexp(str string) gigaparsec.Parser[byte, []byte] {
 	if !strings.HasPrefix(str, "^") && !strings.HasPrefix(str, `\A`) {
 		str = "^" + str
@@ -49,7 +57,10 @@ func Regexp(str string) gigaparsec.Parser[byte, []byte] {
 	return func(input gigaparsec.State[byte]) (gigaparsec.Result[byte, []byte], error) {
 		r := NewRuneReader(input.Cursor())
 		idx := re.FindReaderIndex(r)
-		// TODO Check error from r; this requires an Error() method on cursor.RuneReader.
+		err := r.Error()
+		if err != nil && !errors.Is(err, io.EOF) {
+			return gigaparsec.Result[byte, []byte]{}, fmt.Errorf("Regexp: reader error: %w", err)
+		}
 		if idx == nil {
 			return gigaparsec.Fail[byte, []byte](false, gigaparsec.Message{
 				Pos:      input.Pos(),
@@ -65,7 +76,7 @@ func Regexp(str string) gigaparsec.Parser[byte, []byte] {
 		n, _, err := input.Cursor().Read(dst)
 		if err != nil {
 			// If we can't access those same bytes again, something is wrong.
-			return gigaparsec.Result[byte, []byte]{}, fmt.Errorf("Regex: unexpected error: %w", err)
+			return gigaparsec.Result[byte, []byte]{}, fmt.Errorf("Regexp: unexpected error: %w", err)
 		}
 		next := input.At(input.Pos() + n)
 		return gigaparsec.Succeed(true, dst, next, gigaparsec.MessageOK(input.Pos())), nil