fix: LineFilterLabelFilter.String() regexp correct delimiters

pkg/logql/log/label_filter.go

@@ -393,7 +393,12 @@ type LineFilterLabelFilter struct {
 func (s *LineFilterLabelFilter) String() string {
 	if unwrappedFilter, ok := s.Filter.(regexpFilter); ok {
 		rStr := unwrappedFilter.String()
-		str := fmt.Sprintf("%s%s`%s`", s.Matcher.Name, s.Matcher.Type, rStr)
+		if strings.Contains(rStr, "`") {
+			rStr = strconv.Quote(rStr)
+		} else {
+			rStr = fmt.Sprintf("`%s`", rStr)
+		}
+		str := fmt.Sprintf("%s%s%s", s.Matcher.Name, s.Matcher.Type, rStr)
 		return str
 	}
 	return s.Matcher.String()

pkg/logql/log/label_filter_test.go

@@ -474,3 +474,51 @@ func BenchmarkLineLabelFilters(b *testing.B) {
 		})
 	}
 }
+
+func TestLineFilterLabelFilter_String(t *testing.T) {
+	type fields struct {
+		Matcher *labels.Matcher
+		Filter  Filterer
+	}
+	tests := []struct {
+		name   string
+		fields fields
+		want   string
+	}{
+		{
+			name: "it correctly surrounds regex containing backticks with double quotes",
+			fields: fields{
+				Matcher: labels.MustNewMatcher(labels.MatchRegexp, "msg", "`.`"),
+				Filter:  mustFilter(newRegexpFilter("`.`", "`.`", true)),
+			},
+			want: "msg=~\"`.`\"",
+		},
+		{
+			name: "it correctly surrounds regex containing double quote with backticks",
+			fields: fields{
+				Matcher: labels.MustNewMatcher(labels.MatchRegexp, "msg", `"`),
+				Filter:  mustFilter(newRegexpFilter(`"`, `"`, true)),
+			},
+			want: "msg=~`\"`",
+		},
+		{
+			name: "it correctly surrounds regex containing both backticks and double quotes with double quotes",
+			fields: fields{
+				Matcher: labels.MustNewMatcher(labels.MatchRegexp, "msg", "`\""),
+				Filter:  mustFilter(newRegexpFilter("`\"", "`\"", true)),
+			},
+			want: "msg=~\"`\\\"\"",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			s := &LineFilterLabelFilter{
+				Matcher: tt.fields.Matcher,
+				Filter:  tt.fields.Filter,
+			}
+			if got := s.String(); got != tt.want {
+				t.Errorf("LineFilterLabelFilter.String() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

pkg/logql/syntax/parser_test.go

@@ -356,6 +356,16 @@ var ParseTestCases = []struct {
 			Without: false,
 		}, nil),
 	},
+	{
+		in: "{ foo = \"bar\" } | logfmt | msg =~ \"`.`\" ",
+		exp: newPipelineExpr(
+			newMatcherExpr([]*labels.Matcher{mustNewMatcher(labels.MatchEqual, "foo", "bar")}),
+			MultiStageExpr{
+				newLogfmtParserExpr(nil),
+				newLabelFilterExpr(log.NewStringLabelFilter(mustNewMatcher(labels.MatchRegexp, "msg", "`.`"))),
+			},
+		),
+	},
 	{
 		in:  `unk({ foo = "bar" }[5m])`,
 		err: logqlmodel.NewParseError("syntax error: unexpected IDENTIFIER", 1, 1),
@@ -3714,4 +3724,11 @@ func TestParseSampleExpr_String(t *testing.T) {
 		// escaping is hard: the result is {cluster="beep", namespace="boop"} | msg=~`\w.*` which is equivalent to the original
 		require.Equal(t, "{cluster=\"beep\", namespace=\"boop\"} | msg=~`\\w.*`", expr.String())
 	})
+
+	t.Run("it correctly surrounds regex containing backticks with double quotes", func(t *testing.T) {
+		query := "{foo=\"bar\"} | logfmt | msg=~\"`.\\\"`\""
+		expr, err := ParseExpr(query)
+		require.NoError(t, err)
+		require.Equal(t, query, expr.String())
+	})
 }