grep: fixes erroneous output of grep in forward order (issue3885) If grep is passed a revset in forwards order via -r , say -r 0:tip Then the output is erroneous. This patch fixes that. The output was wrong because we deleted the last revision key in the matches and when we moved to the next revision we didn't had this to compare the diff. So the pstates dict was always empty and in the SequenceMatcher, to convert and empty pstate to the states dictionary you would always insert. This patch keeps the matches dictionary until the end of this window and clears it at once when this window ends. This solves the above mentioned problem and also do not cause any memory leak.