log: add --show-linear-break to help see non-linear history

Option explanation is in rev-list-options.txt. The interaction with -z
is left undecided.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 45 insertions, 3 deletions

diff --git a/revision.c b/revision.c
index a68fde6e9..05b76c796 100644
--- a/revision.c
+++ b/revision.c
@@ -1832,6 +1832,14 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		revs->notes_opt.use_default_notes = 1;
 	} else if (!strcmp(arg, "--show-signature")) {
 		revs->show_signature = 1;
+	} else if (!strcmp(arg, "--show-linear-break") ||
+		   starts_with(arg, "--show-linear-break=")) {
+		if (starts_with(arg, "--show-linear-break="))
+			revs->break_bar = xstrdup(arg + 20);
+		else
+			revs->break_bar = "                    ..........";
+		revs->track_linear = 1;
+		revs->track_first_time = 1;
 	} else if (starts_with(arg, "--show-notes=") ||
 		   starts_with(arg, "--notes=")) {
 		struct strbuf buf = STRBUF_INIT;
@@ -1955,6 +1963,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 			unkv[(*unkc)++] = arg;
 		return opts;
 	}
+	if (revs->graph && revs->track_linear)
+		die("--show-linear-break and --graph are incompatible");
 
 	return 1;
 }
@@ -2897,6 +2907,27 @@ enum commit_action simplify_commit(struct rev_info *revs, struct commit *commit)
 	return action;
 }
 
+static void track_linear(struct rev_info *revs, struct commit *commit)
+{
+	if (revs->track_first_time) {
+		revs->linear = 1;
+		revs->track_first_time = 0;
+	} else {
+		struct commit_list *p;
+		for (p = revs->previous_parents; p; p = p->next)
+			if (p->item == NULL || /* first commit */
+			    !hashcmp(p->item->object.sha1, commit->object.sha1))
+				break;
+		revs->linear = p != NULL;
+	}
+	if (revs->reverse) {
+		if (revs->linear)
+			commit->object.flags |= TRACK_LINEAR;
+	}
+	free_commit_list(revs->previous_parents);
+	revs->previous_parents = copy_commit_list(commit->parents);
+}
+
 static struct commit *get_revision_1(struct rev_info *revs)
 {
 	if (!revs->commits)
@@ -2936,6 +2967,8 @@ static struct commit *get_revision_1(struct rev_info *revs)
 			die("Failed to simplify parents of commit %s",
 			    sha1_to_hex(commit->object.sha1));
 		default:
+			if (revs->track_linear)
+				track_linear(revs, commit);
 			return commit;
 		}
 	} while (revs->commits);
@@ -3102,14 +3135,23 @@ struct commit *get_revision(struct rev_info *revs)
 		revs->reverse_output_stage = 1;
 	}
 
-	if (revs->reverse_output_stage)
-		return pop_commit(&revs->commits);
+	if (revs->reverse_output_stage) {
+		c = pop_commit(&revs->commits);
+		if (revs->track_linear)
+			revs->linear = !!(c && c->object.flags & TRACK_LINEAR);
+		return c;
+	}
 
 	c = get_revision_internal(revs);
 	if (c && revs->graph)
 		graph_update(revs->graph, c);
-	if (!c)
+	if (!c) {
 		free_saved_parents(revs);
+		if (revs->previous_parents) {
+			free_commit_list(revs->previous_parents);
+			revs->previous_parents = NULL;
+		}
+	}
 	return c;
 }