add explanatory comments

Author: vladak

opengrok-indexer/src/main/java/org/opengrok/indexer/history/SCCSRepository.java

@@ -62,6 +62,11 @@ public class SCCSRepository extends Repository {
 
     public SCCSRepository() {
         type = "SCCS";
+        /*
+         * Originally there was only the "yy/MM/dd" pattern however the newer SCCS implementations seem
+         * to use the time as well. Some historical SCCS versions might still use that, so it is left there
+         * for potential compatibility.
+         */
         datePatterns = new String[]{
             "yy/MM/dd HH:mm:ss",
             "yy/MM/dd"

opengrok-indexer/src/test/java/org/opengrok/indexer/history/SCCSRepositoryTest.java

@@ -144,6 +144,12 @@ void testGetHistory() throws Exception {
         assertTrue(file.isFile());
         History history = sccsRepository.getHistory(file);
         assertNotNull(history);
+        /*
+         * SCCSRepository code parses the contents of the "s." files directly.
+         * The time strings embedded therein do not contain time zone so the expected date values
+         * in the HistoryEntry list are constructed using zone-less time value
+         * instead of time stamp in long to avoid mismatch due to time zone recalculation.
+         */
         DateFormat dateFormat = new SimpleDateFormat("EEE MMM dd HH:mm:ss yyyy");
         List<HistoryEntry> entries = List.of(
                 new HistoryEntry("1.2", dateFormat.parse("Tue Aug 12 22:11:54 2008"),