Merge branch 'ds/commit-graph-incremental'

The commits in a repository can be described by multiple
commit-graph files now, which allows the commit-graph files to be
updated incrementally.

* ds/commit-graph-incremental:
  commit-graph: test verify across alternates
  commit-graph: normalize commit-graph filenames
  commit-graph: test --split across alternate without --split
  commit-graph: test octopus merges with --split
  commit-graph: clean up chains after flattened write
  commit-graph: verify chains with --shallow mode
  commit-graph: create options for split files
  commit-graph: expire commit-graph files
  commit-graph: allow cross-alternate chains
  commit-graph: merge commit-graph chains
  commit-graph: add --split option to builtin
  commit-graph: write commit-graph chains
  commit-graph: rearrange chunk count logic
  commit-graph: add base graphs chunk
  commit-graph: load commit-graph chains
  commit-graph: rename commit_compare to oid_compare
  commit-graph: prepare for commit-graph chains
  commit-graph: document commit-graph chains

builtin/commit.c

@@ -1687,7 +1687,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		      "not exceeded, and then \"git restore --staged :/\" to recover."));
 
 	if (git_env_bool(GIT_TEST_COMMIT_GRAPH, 0) &&
-	    write_commit_graph_reachable(get_object_directory(), 0))
+	    write_commit_graph_reachable(get_object_directory(), 0, NULL))
 		return 1;
 
 	repo_rerere(the_repository, 0);