Extended SHA1 -- "rev^@" syntax to mean "all parents"

A short-hand "rev^@" is understood to be "all parents of the
named commit" with this patch.  So you can do

	git show v1.0.0^@

to view the parents of a merge commit,

	gitk ^v1.0.0^@ v1.0.4

to view the log between two revs (including the bottom one), and

	git diff --cc v1.1.0 v1.0.0^@

to inspect what got changed from the merge parents of v1.0.0 to v1.1.0.

This might be just my shiny new toy that is not very useful in
practice.  I needed it to do the multi-tree diff on Len's
infamous 12-way Octopus; typing "diff --cc funmerge funmerge^1
funmerge^2 funmerge^3 ..." was too painful.

[jc: taking suggestions from Linus and Johannes to match expectations
from shell users who are used to see $@ or $* either of which makes
sense.  I tend to write "$@" more often so...]

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

1 files changed, 37 insertions, 0 deletions

diff --git a/revision.c b/revision.c
index f2a9f25..d1f85a8 100644
--- a/revision.c
+++ b/revision.c
@@ -477,6 +477,36 @@ static void handle_all(struct rev_info *revs, unsigned flags)
 	for_each_ref(handle_one_ref);
 }
 
+static int add_parents_only(struct rev_info *revs, const char *arg, int flags)
+{
+	unsigned char sha1[20];
+	struct object *it;
+	struct commit *commit;
+	struct commit_list *parents;
+
+	if (*arg == '^') {
+		flags ^= UNINTERESTING;
+		arg++;
+	}
+	if (get_sha1(arg, sha1))
+		return 0;
+	while (1) {
+		it = get_reference(revs, arg, sha1, 0);
+		if (strcmp(it->type, tag_type))
+			break;
+		memcpy(sha1, ((struct tag*)it)->tagged->sha1, 20);
+	}
+	if (strcmp(it->type, commit_type))
+		return 0;
+	commit = (struct commit *)it;
+	for (parents = commit->parents; parents; parents = parents->next) {
+		it = &parents->item->object;
+		it->flags |= flags;
+		add_pending_object(revs, it, arg);
+	}
+	return 1;
+}
+
 void init_revisions(struct rev_info *revs)
 {
 	memset(revs, 0, sizeof(*revs));
@@ -746,6 +776,13 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 			}
 			*dotdot = '.';
 		}
+		dotdot = strstr(arg, "^@");
+		if (dotdot && !dotdot[2]) {
+			*dotdot = 0;
+			if (add_parents_only(revs, arg, flags))
+				continue;
+			*dotdot = '^';
+		}
 		local_flags = 0;
 		if (*arg == '^') {
 			local_flags = UNINTERESTING;