repochecker/grammalecte: Refactor grammar passage extraction

repochecker/grammalecte/lib/errors.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"strings"
+	"unicode/utf8"
 )
 
 const LOG_PREFIX_LEN = 20
@@ -72,6 +73,22 @@ func (e GrammarError) Error() string {
 	)
 }
 
+func (e GrammarError) GetPassage() string {
+	nb := 0
+	var ret []byte
+	for _, r := range e.Source {
+		if nb >= e.End {
+			break
+		}
+		if nb >= e.Start {
+			ret = utf8.AppendRune(ret, r)
+		}
+		nb += 1
+	}
+
+	return string(ret)
+}
+
 func underline(prefix, start, end int) string {
 	var b bytes.Buffer