rev-list --left-right

The output from "symmetric diff", i.e. A...B, does not
distinguish between commits that are reachable from A and the
ones that are reachable from B.  In this picture, such a
symmetric diff includes commits marked with a and b.

         x---b---b  branch B
        / \ /
       /   .
      /   / \
     o---x---a---a  branch A

However, you cannot tell which ones are 'a' and which ones are
'b' from the output.  Sometimes this is frustrating.  This adds
an output option, --left-right, to rev-list.

        rev-list --left-right A...B

would show ones reachable from A prefixed with '<' and the ones
reachable from B prefixed with '>'.

When combined with --boundary, boundary commits (the ones marked
with 'x' in the above picture) are shown with prefix '-', so you
would see list that looks like this:

    git rev-list --left-right --boundary --pretty=oneline A...B

    >bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb 3rd on b
    >bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb 2nd on b
    <aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 3rd on a
    <aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 2nd on a
    -xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 1st on b
    -xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 1st on a

Signed-off-by: Junio C Hamano <junkio@cox.net>

builtin-rev-list.c

@@ -45,6 +45,7 @@ static int bisect_list;
 static int show_timestamp;
 static int hdr_termination;
 static const char *header_prefix;
+static int show_left_right;
 
 static void show_commit(struct commit *commit)
 {
@@ -54,6 +55,12 @@ static void show_commit(struct commit *commit)
 		fputs(header_prefix, stdout);
 	if (commit->object.flags & BOUNDARY)
 		putchar('-');
+	else if (show_left_right) {
+		if (commit->object.flags & SYMMETRIC_LEFT)
+			putchar('<');
+		else
+			putchar('>');
+	}
 	if (revs.abbrev_commit && revs.abbrev)
 		fputs(find_unique_abbrev(commit->object.sha1, revs.abbrev),
 		      stdout);
@@ -240,6 +247,10 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 			bisect_list = 1;
 			continue;
 		}
+		if (!strcmp(arg, "--left-right")) {
+			show_left_right = 1;
+			continue;
+		}
 		if (!strcmp(arg, "--stdin")) {
 			if (read_from_stdin++)
 				die("--stdin given twice?");

commit.c

@@ -868,11 +868,11 @@ void sort_in_topological_order_fn(struct commit_list ** list, int lifo,
 
 /* merge-rebase stuff */
 
-/* bits #0..7 in revision.h */
-#define PARENT1		(1u<< 8)
-#define PARENT2		(1u<< 9)
-#define STALE		(1u<<10)
-#define RESULT		(1u<<11)
+/* bits #0..15 in revision.h */
+#define PARENT1		(1u<<16)
+#define PARENT2		(1u<<17)
+#define STALE		(1u<<18)
+#define RESULT		(1u<<19)
 
 static struct commit *interesting(struct commit_list *list)
 {

revision.c

@@ -344,6 +344,7 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
 static void add_parents_to_list(struct rev_info *revs, struct commit *commit, struct commit_list **list)
 {
 	struct commit_list *parent = commit->parents;
+	unsigned left_flag;
 
 	if (commit->object.flags & ADDED)
 		return;
@@ -388,6 +389,7 @@ static void add_parents_to_list(struct rev_info *revs, struct commit *commit, st
 	if (revs->no_walk)
 		return;
 
+	left_flag = (commit->object.flags & SYMMETRIC_LEFT);
 	parent = commit->parents;
 	while (parent) {
 		struct commit *p = parent->item;
@@ -395,6 +397,7 @@ static void add_parents_to_list(struct rev_info *revs, struct commit *commit, st
 		parent = parent->next;
 
 		parse_commit(p);
+		p->object.flags |= left_flag;
 		if (p->object.flags & SEEN)
 			continue;
 		p->object.flags |= SEEN;
@@ -640,7 +643,7 @@ int handle_revision_arg(const char *arg, struct rev_info *revs,
 				add_pending_commit_list(revs, exclude,
 							flags_exclude);
 				free_commit_list(exclude);
-				a->object.flags |= flags;
+				a->object.flags |= flags | SYMMETRIC_LEFT;
 			} else
 				a->object.flags |= flags_exclude;
 			b->object.flags |= flags;

revision.h

@@ -9,6 +9,7 @@
 #define BOUNDARY	(1u<<5)
 #define BOUNDARY_SHOW	(1u<<6)
 #define ADDED		(1u<<7)	/* Parents already parsed and added? */
+#define SYMMETRIC_LEFT	(1u<<8)
 
 struct rev_info;
 struct log_info;