Fix RuneReader breaking right before EOF

bytes/regexp.go

@@ -35,10 +35,14 @@ func (rr *RuneReader) ReadRune() (r rune, size int, err error) {
 		rr.cursor = next
 		return 0, 0, fmt.Errorf("ReadRune: %w", err)
 	}
+	if n == 0 {
+		return 0, 0, io.EOF
+	}
 	s = s[:n]
+	fmt.Println("read bytes:", s)
 	r, size = utf8.DecodeRune(s)
 	rr.cursor = rr.cursor.At(rr.cursor.Pos() + uint64(size))
-	return r, size, err
+	return r, size, nil
 }
 
 func (rr *RuneReader) Cursor() cursor.Cursor[byte] {

bytes/regexp_test.go

@@ -1,6 +1,15 @@
 package bytes_test
 
-import "testing"
+import (
+	"testing"
+
+	"git.codemonkeysoftware.net/b/gigaparsec"
+	"git.codemonkeysoftware.net/b/gigaparsec/bytes"
+	"git.codemonkeysoftware.net/b/gigaparsec/cursor"
+	"github.com/shoenig/test"
+	"github.com/shoenig/test/must"
+	"pgregory.net/rapid"
+)
 
 func Todo(t *testing.T) {
 	t.Fatalf("TODO")
@@ -10,9 +19,31 @@ func TestRegexp(t *testing.T) {
 	t.Run("only searches the beginning of input", Todo)
 	t.Run("position is correct after match", Todo)
 	t.Run("fails on unexpected error", Todo)
-	t.Run("returns a useful Got value", Todo)
+	t.Run("returns a useful Got value", rapid.MakeCheck(func(t *rapid.T) {
+
+	}))
+	t.Run("basically works", func(t *testing.T) {
+		result, err := bytes.Regexp("a")(gigaparsec.MakeState(cursor.NewSlice([]byte("a"))))
+		must.NoError(t, err)
+		failed, _, msg := result.Failed()
+		must.False(t, failed, must.Sprint(msg))
+		succeeded, consumed, value, _, _ := result.Succeeded()
+		test.True(t, succeeded)
+		test.True(t, consumed)
+		test.EqOp(t, "a", value)
+	})
 }
 
 func TestRuneReader(t *testing.T) {
-	Todo(t)
+	var s = []byte("abcdefghijklmnopqrstuvwxyz")
+	rr := bytes.NewRuneReader(cursor.NewSlice(s))
+	for i, b := range s {
+		r, n, err := rr.ReadRune()
+		test.NoError(t, err)
+		test.EqOp(t, 1, n)
+		test.EqOp(t, r, rune(b))
+		if t.Failed() {
+			t.Fatalf("failed at %d", i)
+		}
+	}
 }