revision.c: remove duplicated parents after history simplification

When we simplify history due to path limits, the parents list
for a rewritten commit can end up having duplicates.  Instead of
filtering them out in the output codepath like earlier commit
8849442 did, remove them much earlier, when the parent
information actually gets rewritten.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.c

@@ -1308,6 +1308,25 @@ static enum rewrite_result rewrite_one(struct rev_info *revs, struct commit **pp
 	}
 }
 
+static void remove_duplicate_parents(struct commit *commit)
+{
+	struct commit_list *p;
+	struct commit_list **pp = &commit->parents;
+
+	/* Examine existing parents while marking ones we have seen... */
+	for (p = commit->parents; p; p = p->next) {
+		struct commit *parent = p->item;
+		if (parent->object.flags & TMP_MARK)
+			continue;
+		parent->object.flags |= TMP_MARK;
+		*pp = p;
+		pp = &p->next;
+	}
+	/* ... and clear the temporary mark */
+	for (p = commit->parents; p; p = p->next)
+		p->item->object.flags &= ~TMP_MARK;
+}
+
 static int rewrite_parents(struct rev_info *revs, struct commit *commit)
 {
 	struct commit_list **pp = &commit->parents;
@@ -1324,6 +1343,7 @@ static int rewrite_parents(struct rev_info *revs, struct commit *commit)
 		}
 		pp = &parent->next;
 	}
+	remove_duplicate_parents(commit);
 	return 0;
 }