[PATCH v3 2/8] commit-graph.c: show progress of finding reachable commits

[Taylor Blau <me@ttaylorr.com>]

When 'git commit-graph write --reachable' is invoked, the commit-graph
machinery calls 'for_each_ref()' to discover the set of reachable
commits.

Right now the 'add_ref_to_set' callback is not doing anything other than
adding an OID to the set of known-reachable OIDs. In a subsequent
commit, 'add_ref_to_set' will presumptively peel references. This
operation should be fast for repositories with an up-to-date
'$GIT_DIR/packed-refs', but may be slow in the general case.

So that it doesn't appear that 'git commit-graph write' is idling with
'--reachable' in the slow case, add a progress meter to provide some
output in the meantime.

In general, we don't expect a progress meter to appear at all, since
peeling references with a 'packed-refs' file is quick. If it's slow and
we do show a progress meter, the subsequent 'fill_oids_from_commits()'
will be fast, since all of the calls to
'lookup_commit_reference_gently()' will be no-ops.

Both progress meters are delayed, so it is unlikely that more than one
will appear. In either case, this intermediate state will go away in a
handful of patches, at which point there will be at most one progress
meter.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 commit-graph.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/commit-graph.c b/commit-graph.c
index 9693112063..f855911320 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1321,6 +1321,7 @@ static void compute_bloom_filters(struct write_commit_graph_context *ctx)
 
 struct refs_cb_data {
 	struct oidset *commits;
+	struct progress *progress;
 };
 
 static int add_ref_to_set(const char *refname,
@@ -1330,6 +1331,9 @@ static int add_ref_to_set(const char *refname,
 	struct refs_cb_data *data = (struct refs_cb_data *)cb_data;
 
 	oidset_insert(data->commits, oid);
+
+	display_progress(data->progress, oidset_size(data->commits));
+
 	return 0;
 }
 
@@ -1343,12 +1347,17 @@ int write_commit_graph_reachable(struct object_directory *odb,
 
 	memset(&data, 0, sizeof(data));
 	data.commits = &commits;
+	if (flags & COMMIT_GRAPH_WRITE_PROGRESS)
+		data.progress = start_delayed_progress(
+			_("Collecting referenced commits"), 0);
 
 	for_each_ref(add_ref_to_set, &data);
 	result = write_commit_graph(odb, NULL, &commits,
 				    flags, split_opts);
 
 	oidset_clear(&commits);
+	if (data.progress)
+		stop_progress(&data.progress);
 	return result;
 }
 
-- 
2.26.0.113.ge9739cdccc