Revert "Stopped String() from doubly escaping regex characters" (#10318)

Reverts grafana/loki#10277

This currently breaks and cause panics for query with regex label
matcher. Reverting it till we find the fix.

pkg/logql/log/label_filter.go

@@ -368,16 +368,6 @@ type lineFilterLabelFilter struct {
 	filter Filterer
 }
 
-// overrides the matcher.String() function in case there is a regexpFilter
-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)
-		return str
-	}
-	return s.Matcher.String()
-}
-
 func (s *lineFilterLabelFilter) Process(_ int64, line []byte, lbs *LabelsBuilder) ([]byte, bool) {
 	v := labelValue(s.Name, lbs)
 	return line, s.filter.Filter(unsafeGetBytes(v))

pkg/logql/syntax/parser_test.go

@@ -3465,13 +3465,3 @@ func TestNoOpLabelToString(t *testing.T) {
 	require.NoError(t, err)
 	require.Len(t, stages, 0)
 }
-
-// Tests that the regex part of expr doesn't get doubly escaped when we call expr.String()
-func TestParseSampleExpr_String(t *testing.T) {
-	query := `sum(rate({cluster="beep", namespace="boop"} | msg=~` + "`" + `.*?(GET|POST|PUT|DELETE|PATCH|HEAD|OPTIONS) /loki/api/(?i)(\d+[a-z]|[a-z]+\d)\w*/query_range` + "`" + `[1d]))`
-	expr, err := ParseSampleExpr(query)
-	require.NoError(t, err)
-	// need to change some backticks to " in order for query to be exactly equal to expr.String(), otherwise it's the same query
-	expected := `sum(rate({cluster="beep", namespace="boop"} | msg=~".*?(GET|POST|PUT|DELETE|PATCH|HEAD|OPTIONS) /loki/api/(?i)(\d+[a-z]|[a-z]+\d)\w*/query_range"[1d]))`
-	require.Equal(t, expected, expr.String())
-}