revision: --skip=<n>

This adds --skip=<n> option to revision traversal machinery.
Documentation and test were added by Robert Fitzsimons.

Signed-off-by: Robert Fitzsimons <robfitz@273k.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 32 insertions, 14 deletions

diff --git a/revision.c b/revision.c
index 7b6f91f83e..5dc1e70260 100644
--- a/revision.c
+++ b/revision.c
@@ -523,6 +523,7 @@ void init_revisions(struct rev_info *revs, const char *prefix)
 	revs->prefix = prefix;
 	revs->max_age = -1;
 	revs->min_age = -1;
+	revs->skip_count = -1;
 	revs->max_count = -1;
 
 	revs->prune_fn = NULL;
@@ -759,6 +760,10 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 				revs->max_count = atoi(arg + 12);
 				continue;
 			}
+			if (!strncmp(arg, "--skip=", 7)) {
+				revs->skip_count = atoi(arg + 7);
+				continue;
+			}
 			/* accept -<digit>, like traditional "head" */
 			if ((*arg == '-') && isdigit(arg[1])) {
 				revs->max_count = atoi(arg + 1);
@@ -1122,23 +1127,11 @@ static int commit_match(struct commit *commit, struct rev_info *opt)
 			   commit->buffer, strlen(commit->buffer));
 }
 
-struct commit *get_revision(struct rev_info *revs)
+static struct commit *get_revision_1(struct rev_info *revs)
 {
-	struct commit_list *list = revs->commits;
-
-	if (!list)
+	if (!revs->commits)
 		return NULL;
 
-	/* Check the max_count ... */
-	switch (revs->max_count) {
-	case -1:
-		break;
-	case 0:
-		return NULL;
-	default:
-		revs->max_count--;
-	}
-
 	do {
 		struct commit_list *entry = revs->commits;
 		struct commit *commit = entry->item;
@@ -1205,3 +1198,28 @@ struct commit *get_revision(struct rev_info *revs)
 	} while (revs->commits);
 	return NULL;
 }
+
+struct commit *get_revision(struct rev_info *revs)
+{
+	struct commit *c = NULL;
+
+	if (0 < revs->skip_count) {
+		while ((c = get_revision_1(revs)) != NULL) {
+			if (revs->skip_count-- <= 0)
+				break;
+		}
+	}
+
+	/* Check the max_count ... */
+	switch (revs->max_count) {
+	case -1:
+		break;
+	case 0:
+		return NULL;
+	default:
+		revs->max_count--;
+	}
+	if (c)
+		return c;
+	return get_revision_1(revs);
+}