fix(logql): updated JSONExpressionParser not to unescape extracted values if it is JSON object. (#14499)

Signed-off-by: Vladyslav Diachenko <vlad.diachenko@grafana.com>

pkg/logql/log/parser.go

@@ -625,6 +625,8 @@ func (j *JSONExpressionParser) Process(_ int64, line []byte, lbs *LabelsBuilder)
 		switch typ {
 		case jsonparser.Null:
 			lbs.Set(ParsedLabel, key, "")
+		case jsonparser.Object:
+			lbs.Set(ParsedLabel, key, string(data))
 		default:
 			lbs.Set(ParsedLabel, key, unescapeJSONString(data))
 		}

pkg/logql/log/parser_test.go

@@ -542,13 +542,35 @@ func TestJSONExpressionParser(t *testing.T) {
 			),
 			NoParserHints(),
 		},
+		{
+			"nested object with escaped value",
+			[]byte(`{"app":{"name":"great \"loki\""}`),
+			[]LabelExtractionExpr{
+				NewLabelExtractionExpr("app", `app`),
+			},
+			labels.FromStrings("foo", "bar"),
+			labels.FromStrings("foo", "bar",
+				"app", `{"name":"great \"loki\""}`,
+			),
+			NoParserHints(),
+		},
+		{
+			"field with escaped value inside the json string",
+			[]byte(`{"app":"{\"name\":\"great \\\"loki\\\"\"}"}`),
+			[]LabelExtractionExpr{
+				NewLabelExtractionExpr("app", `app`),
+			},
+			labels.FromStrings("foo", "bar"),
+			labels.FromStrings("foo", "bar",
+				"app", `{"name":"great \"loki\""}`,
+			),
+			NoParserHints(),
+		},
 	}
 	for _, tt := range tests {
-		j, err := NewJSONExpressionParser(tt.expressions)
-		if err != nil {
-			t.Fatalf("cannot create JSON expression parser: %s", err.Error())
-		}
 		t.Run(tt.name, func(t *testing.T) {
+			j, err := NewJSONExpressionParser(tt.expressions)
+			require.NoError(t, err, "cannot create JSON expression parser")
 			b := NewBaseLabelsBuilderWithGrouping(nil, tt.hints, false, false).ForLabels(tt.lbs, tt.lbs.Hash())
 			b.Reset()
 			_, _ = j.Process(0, tt.line, b)