revision: introduce rev_walk_mode to clarify get_revision_1()

get_revision_1() dispatches to different walk strategies based on a
combination of rev_info flags: reflog_info, topo_walk_info, limited,
and no_walk.  These conditions are checked in multiple places within
the function — once to select the next commit, and again to decide
how to expand parents — and the two chains must stay in sync.

Extract the mode selection into a rev_walk_mode enum and a small
get_walk_mode() helper, resolved once at the top of get_revision_1().
Both dispatch sites now switch on the same mode variable, making it
obvious that they agree and easier to verify that all modes are
handled.

No functional change.

Signed-off-by: Kristofer Karlsson <krka@spotify.com>

Author: spkrka

revision.c

@@ -4322,49 +4322,87 @@ static void track_linear(struct rev_info *revs, struct commit *commit)
 	revs->previous_parents = commit_list_copy(commit->parents);
 }
 
+enum rev_walk_mode {
+	REV_WALK_REFLOG,
+	REV_WALK_TOPO,
+	REV_WALK_LIMITED,
+	REV_WALK_NO_WALK,
+	REV_WALK_STREAMING,
+};
+
+static enum rev_walk_mode get_walk_mode(struct rev_info *revs)
+{
+	if (revs->reflog_info)
+		return REV_WALK_REFLOG;
+	if (revs->topo_walk_info)
+		return REV_WALK_TOPO;
+	if (revs->limited)
+		return REV_WALK_LIMITED;
+	if (revs->no_walk)
+		return REV_WALK_NO_WALK;
+	return REV_WALK_STREAMING;
+}
+
 static struct commit *get_revision_1(struct rev_info *revs)
 {
+	enum rev_walk_mode mode = get_walk_mode(revs);
+
+	if (mode == REV_WALK_STREAMING && revs->commits)
+		rev_info_commit_list_to_queue(revs);
+
 	while (1) {
 		struct commit *commit;
 
-		if (revs->reflog_info)
+		switch (mode) {
+		case REV_WALK_REFLOG:
 			commit = next_reflog_entry(revs->reflog_info);
-		else if (revs->topo_walk_info)
+			break;
+		case REV_WALK_TOPO:
 			commit = next_topo_commit(revs);
-		else if (revs->limited || revs->no_walk)
+			break;
+		case REV_WALK_LIMITED:
+		case REV_WALK_NO_WALK:
 			commit = pop_commit(&revs->commits);
-		else {
-			if (!revs->commit_queue.nr && revs->commits)
-				rev_info_commit_list_to_queue(revs);
+			break;
+		case REV_WALK_STREAMING:
 			commit = prio_queue_get(&revs->commit_queue);
+			break;
 		}
 
 		if (!commit)
 			return NULL;
 
-		if (revs->reflog_info)
+		if (mode == REV_WALK_REFLOG)
 			commit->object.flags &= ~(ADDED | SEEN | SHOWN);
 
 		/*
 		 * If we haven't done the list limiting, we need to look at
 		 * the parents here. We also need to do the date-based limiting
 		 * that we'd otherwise have done in limit_list().
 		 */
-		if (!revs->limited) {
+		if (mode != REV_WALK_LIMITED) {
 			if (revs->max_age != -1 &&
 			    comparison_date(revs, commit) < revs->max_age)
 				continue;
 
-			if (revs->reflog_info)
+			switch (mode) {
+			case REV_WALK_REFLOG:
 				try_to_simplify_commit(revs, commit);
-			else if (revs->topo_walk_info)
+				break;
+			case REV_WALK_TOPO:
 				expand_topo_walk(revs, commit);
-			else if (process_parents(revs, commit,
-					revs->no_walk ?
-					NULL : &revs->commit_queue) < 0) {
-				if (!revs->ignore_missing_links)
-					die("Failed to traverse parents of commit %s",
-						oid_to_hex(&commit->object.oid));
+				break;
+			case REV_WALK_STREAMING:
+				if (process_parents(revs, commit,
+						    &revs->commit_queue) < 0) {
+					if (!revs->ignore_missing_links)
+						die("Failed to traverse parents of commit %s",
+						    oid_to_hex(&commit->object.oid));
+				}
+				break;
+			case REV_WALK_NO_WALK:
+			case REV_WALK_LIMITED:
+				break;
 			}
 		}