commit-graph: introduce 'commitGraph.maxNewFilters'

Introduce a configuration variable to specify a default value for the
recently-introduce '--max-new-filters' option of 'git commit-graph
write'.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/commitgraph.txt

@@ -1,3 +1,7 @@
+commitGraph.maxNewFilters::
+	Specifies the default value for the `--max-new-filters` option of `git
+	commit-graph write` (c.f., linkgit:git-commit-graph[1]).
+
 commitGraph.readChangedPaths::
 	If true, then git will use the changed-path Bloom filters in the
 	commit-graph file (if it exists, and they are present). Defaults to

Documentation/git-commit-graph.txt

@@ -71,7 +71,8 @@ With the `--max-new-filters=<n>` option, generate at most `n` new Bloom
 filters (if `--changed-paths` is specified). If `n` is `-1`, no limit is
 enforced. Only commits present in the new layer count against this
 limit. To retroactively compute Bloom filters over earlier layers, it is
-advised to use `--split=replace`.
+advised to use `--split=replace`.  Overrides the `commitGraph.maxNewFilters`
+configuration.
 +
 With the `--split[=<strategy>]` option, write the commit-graph as a
 chain of multiple commit-graph files stored in

builtin/commit-graph.c

@@ -181,6 +181,18 @@ static int write_option_max_new_filters(const struct option *opt,
 	return 0;
 }
 
+static int git_commit_graph_write_config(const char *var, const char *value,
+					 void *cb)
+{
+	if (!strcmp(var, "commitgraph.maxnewfilters"))
+		write_opts.max_new_filters = git_config_int(var, value);
+	/*
+	 * No need to fall-back to 'git_default_config', since this was already
+	 * called in 'cmd_commit_graph()'.
+	 */
+	return 0;
+}
+
 static int graph_write(int argc, const char **argv)
 {
 	struct string_list pack_indexes = STRING_LIST_INIT_NODUP;
@@ -231,6 +243,8 @@ static int graph_write(int argc, const char **argv)
 
 	trace2_cmd_mode("write");
 
+	git_config(git_commit_graph_write_config, &opts);
+
 	argc = parse_options(argc, argv, NULL,
 			     builtin_commit_graph_write_options,
 			     builtin_commit_graph_write_usage, 0);

t/t4216-log-bloom.sh

@@ -325,13 +325,15 @@ test_expect_success 'Bloom generation is limited by --max-new-filters' '
 '
 
 test_expect_success 'Bloom generation backfills previously-skipped filters' '
+	# Check specifying commitGraph.maxNewFilters over "git config" works.
+	test_config -C limits commitGraph.maxNewFilters 1 &&
 	(
 		cd limits &&
 
 		rm -f trace.event &&
 		GIT_TRACE2_EVENT="$(pwd)/trace.event" \
 			git commit-graph write --reachable --changed-paths \
-				--split=replace --max-new-filters=1 &&
+				--split=replace &&
 		test_filter_computed 1 trace.event &&
 		test_filter_not_computed 4 trace.event &&
 		test_filter_trunc_empty 0 trace.event &&
@@ -339,6 +341,26 @@ test_expect_success 'Bloom generation backfills previously-skipped filters' '
 	)
 '
 
+test_expect_success '--max-new-filters overrides configuration' '
+	git init override &&
+	test_when_finished "rm -fr override" &&
+	test_config -C override commitGraph.maxNewFilters 2 &&
+	(
+		cd override &&
+		test_commit one &&
+		test_commit two &&
+
+		rm -f trace.event &&
+		GIT_TRACE2_EVENT="$(pwd)/trace.event" \
+			git commit-graph write --reachable --changed-paths \
+				--max-new-filters=1 &&
+		test_filter_computed 1 trace.event &&
+		test_filter_not_computed 1 trace.event &&
+		test_filter_trunc_empty 0 trace.event &&
+		test_filter_trunc_large 0 trace.event
+	)
+'
+
 test_expect_success 'Bloom generation backfills empty commits' '
 	git init empty &&
 	test_when_finished "rm -fr empty" &&