fetch: add fetch.writeCommitGraph config setting

The commit-graph feature is now on by default, and is being
written during 'git gc' by default. Typically, Git only writes
a commit-graph when a 'git gc --auto' command passes the gc.auto
setting to actualy do work. This means that a commit-graph will
typically fall behind the commits that are being used every day.

To stay updated with the latest commits, add a step to 'git
fetch' to write a commit-graph after fetching new objects. The
fetch.writeCommitGraph config setting enables writing a split
commit-graph, so on average the cost of writing this file is
very small. Occasionally, the commit-graph chain will collapse
to a single level, and this could be slow for very large repos.

For additional use, adjust the default to be true when
feature.experimental is enabled.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 53ce99d2bb..d36a403859 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -23,6 +23,7 @@
 #include "packfile.h"
 #include "list-objects-filter-options.h"
 #include "commit-reach.h"
+#include "commit-graph.h"
 
 #define FORCED_UPDATES_DELAY_WARNING_IN_MS (10 * 1000)
 
@@ -1715,6 +1716,20 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 
 	string_list_clear(&list, 0);
 
+	prepare_repo_settings(the_repository);
+	if (the_repository->settings.fetch_write_commit_graph) {
+		int commit_graph_flags = COMMIT_GRAPH_SPLIT;
+		struct split_commit_graph_opts split_opts;
+		memset(&split_opts, 0, sizeof(struct split_commit_graph_opts));
+
+		if (progress)
+			commit_graph_flags |= COMMIT_GRAPH_PROGRESS;
+
+		write_commit_graph_reachable(get_object_directory(),
+					     commit_graph_flags,
+					     &split_opts);
+	}
+
 	close_object_store(the_repository->objects);
 
 	if (enable_auto_gc) {