reflog-walk: apply --since/--until to reflog dates

When doing a reflog walk, we use the commit's date to
do any date limiting. In earlier versions of Git, this could
lead to nonsense results, since a skipped commit would
truncate the traversal. So a sequence like:

  git commit ...
  git checkout week-old-branch
  git checkout -
  git log -g --since=1.day.ago

would stop at the week-old-branch, even though the "git
commit" entry further back is still interesting.

As of the prior commit, which uses a parent-less traversal
of the reflog, you get the whole reflog minus any commits
whose dates do not match the specified options. This is
arguably useful, as you could scan the reflogs for commits
that originated in a certain range.

But more likely a user doing a reflog walk wants to limit
based on the reflog entries themselves. You can simulate
--until with:

  git log -g @{1.day.ago}

but there's no way to ask Git to traverse only back to a
certain date. E.g.:

  # show me reflog entries from the past day
  git log -g --since=1.day.ago

This patch teaches the revision machinery to prefer the
reflog entry dates to the commit dates when doing a reflog
walk. Technically this is a change in behavior that affects
plumbing, but the previous behavior was so buggy that it's
unlikely anyone was relying on it.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

reflog-walk.c

@@ -264,6 +264,18 @@ const char *get_reflog_ident(struct reflog_walk_info *reflog_info)
 	return info->email;
 }
 
+timestamp_t get_reflog_timestamp(struct reflog_walk_info *reflog_info)
+{
+	struct commit_reflog *commit_reflog = reflog_info->last_commit_reflog;
+	struct reflog_info *info;
+
+	if (!commit_reflog)
+		return 0;
+
+	info = &commit_reflog->reflogs->items[commit_reflog->recno+1];
+	return info->timestamp;
+}
+
 void show_reflog_message(struct reflog_walk_info *reflog_info, int oneline,
 			 const struct date_mode *dmode, int force_date)
 {

reflog-walk.h

@@ -13,6 +13,7 @@ extern void show_reflog_message(struct reflog_walk_info *info, int,
 extern void get_reflog_message(struct strbuf *sb,
 		struct reflog_walk_info *reflog_info);
 extern const char *get_reflog_ident(struct reflog_walk_info *reflog_info);
+extern timestamp_t get_reflog_timestamp(struct reflog_walk_info *reflog_info);
 extern void get_reflog_selector(struct strbuf *sb,
 		struct reflog_walk_info *reflog_info,
 		const struct date_mode *dmode, int force_date,

revision.c

@@ -2965,6 +2965,18 @@ static inline int want_ancestry(const struct rev_info *revs)
 	return (revs->rewrite_parents || revs->children.name);
 }
 
+/*
+ * Return a timestamp to be used for --since/--until comparisons for this
+ * commit, based on the revision options.
+ */
+static timestamp_t comparison_date(const struct rev_info *revs,
+				   struct commit *commit)
+{
+	return revs->reflog_info ?
+		get_reflog_timestamp(revs->reflog_info) :
+		commit->date;
+}
+
 enum commit_action get_commit_action(struct rev_info *revs, struct commit *commit)
 {
 	if (commit->object.flags & SHOWN)
@@ -2975,7 +2987,8 @@ enum commit_action get_commit_action(struct rev_info *revs, struct commit *commi
 		return commit_show;
 	if (commit->object.flags & UNINTERESTING)
 		return commit_ignore;
-	if (revs->min_age != -1 && (commit->date > revs->min_age))
+	if (revs->min_age != -1 &&
+	    comparison_date(revs, commit) > revs->min_age)
 			return commit_ignore;
 	if (revs->min_parents || (revs->max_parents >= 0)) {
 		int n = commit_list_count(commit->parents);
@@ -3130,7 +3143,7 @@ static struct commit *get_revision_1(struct rev_info *revs)
 		 */
 		if (!revs->limited) {
 			if (revs->max_age != -1 &&
-			    (commit->date < revs->max_age))
+			    comparison_date(revs, commit) < revs->max_age)
 				continue;
 
 			if (revs->reflog_info)

t/t1414-reflog-walk.sh

@@ -91,6 +91,32 @@ test_expect_success 'date-limiting does not interfere with other logs' '
 	test_cmp expect.all actual
 '
 
+test_expect_success 'min/max age uses entry date to limit' '
+	# Flip between commits one and two so each ref update actually
+	# does something (and does not get optimized out). We know
+	# that the timestamps of those commits will be before our "min".
+
+	git update-ref -m before refs/heads/minmax one &&
+
+	test_tick &&
+	min=$test_tick &&
+	git update-ref -m min refs/heads/minmax two &&
+
+	test_tick &&
+	max=$test_tick &&
+	git update-ref -m max refs/heads/minmax one &&
+
+	test_tick &&
+	git update-ref -m after refs/heads/minmax two &&
+
+	cat >expect <<-\EOF &&
+	max
+	min
+	EOF
+	git log -g --since=$min --until=$max --format=%gs minmax >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'walk prefers reflog to ref tip' '
 	head=$(git rev-parse HEAD) &&
 	one=$(git rev-parse one) &&