Teach revision machinery about --reverse

The option --reverse reverses the order of the commits.

[jc: with comments on rev_info.reverse from Simon 'corecode' Schubert.]

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-rev-list.txt

@@ -27,6 +27,7 @@ SYNOPSIS
 	     [ \--pretty | \--header ]
 	     [ \--bisect ]
 	     [ \--merge ]
+	     [ \--reverse ]
 	     [ \--walk-reflogs ]
 	     <commit>... [ \-- <paths>... ]
 
@@ -266,6 +267,10 @@ By default, the commits are shown in reverse chronological order.
 	parent comes before all of its children, but otherwise things
 	are still ordered in the commit timestamp order.
 
+--reverse::
+
+	Output the commits in reverse order.
+
 Object Traversal
 ~~~~~~~~~~~~~~~~
 

revision.c

@@ -1057,6 +1057,10 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 					git_log_output_encoding = "";
 				continue;
 			}
+			if (!strcmp(arg, "--reverse")) {
+				revs->reverse ^= 1;
+				continue;
+			}
 
 			opts = diff_opt_parse(&revs->diffopt, argv+i, argc-i);
 			if (opts > 0) {
@@ -1285,6 +1289,40 @@ struct commit *get_revision(struct rev_info *revs)
 {
 	struct commit *c = NULL;
 
+	if (revs->reverse) {
+		struct commit_list *list;
+
+		/*
+		 * rev_info.reverse is used to note the fact that we
+		 * want to output the list of revisions in reverse
+		 * order.  To accomplish this goal, reverse can have
+		 * different values:
+		 *
+		 *  0  do nothing
+		 *  1  reverse the list
+		 *  2  internal use:  we have already obtained and
+		 *     reversed the list, now we only need to yield
+		 *     its items.
+		 */
+
+		if (revs->reverse == 1) {
+			revs->reverse = 0;
+			list = NULL;
+			while ((c = get_revision(revs)))
+				commit_list_insert(c, &list);
+			revs->commits = list;
+			revs->reverse = 2;
+		}
+
+		if (!revs->commits)
+			return NULL;
+		c = revs->commits->item;
+		list = revs->commits->next;
+		free(revs->commits);
+		revs->commits = list;
+		return c;
+	}
+
 	if (0 < revs->skip_count) {
 		while ((c = get_revision_1(revs)) != NULL) {
 			if (revs->skip_count-- <= 0)

revision.h

@@ -42,7 +42,8 @@ struct rev_info {
 			unpacked:1, /* see also ignore_packed below */
 			boundary:1,
 			left_right:1,
-			parents:1;
+			parents:1,
+			reverse:2;
 
 	/* Diff flags */
 	unsigned int	diff:1,