[PATCH v5 6/6] connected: add "auto" connectivity check mode

@@ -18,6 +18,12 @@ transfer.connectivityCheck::
 	than `full` when there are many incoming commits.
 	Falls back to `full` for clones, pushes into an empty
 	repository and deepening fetches.
+`auto`;;
+`auto=<cutoff>`;;
+	Choose between `full` and `incremental` with a heuristic.
+	Currently `incremental` is used when there are at most
+	_<cutoff>_ incoming commits (1000 by default), and `full`
+	otherwise.  The heuristic may change in future versions.
 --
 +
 Unknown values are treated as `full`, with a warning.

@@ -1103,7 +1103,7 @@ It is an error to use `--missing-only` without `--missing=print` or
 	traversal, rather than just silencing errors about missing
 	objects.
 
-`--connectivity-check=(full|incremental)`::
+`--connectivity-check=(full|incremental|auto[=<cutoff>])`::
 	(For internal use only.)  Used by `check_connected()` to
 	select the connectivity check algorithm; see
 	`transfer.connectivityCheck` in linkgit:git-config[1].

@@ -29,23 +29,35 @@
 #include "quote.h"
 #include "strbuf.h"
 #include "tree-verify.h"
+#include "parse.h"
+
+#define INCREMENTAL_MAX_COMMITS 1000
 
 enum connectivity_check_mode {
 	CONNECTIVITY_CHECK_FULL,
 	CONNECTIVITY_CHECK_INCREMENTAL,
+	CONNECTIVITY_CHECK_AUTO,
 };
 
 struct connectivity_check {
 	enum connectivity_check_mode mode;
+	unsigned long max_commits;
 };
 
 static void parse_connectivity_check(const char *arg,
 				     struct connectivity_check *check)
 {
+	const char *cutoff;
+
 	if (!strcmp(arg, "full"))
 		check->mode = CONNECTIVITY_CHECK_FULL;
 	else if (!strcmp(arg, "incremental"))
 		check->mode = CONNECTIVITY_CHECK_INCREMENTAL;
+	else if (!strcmp(arg, "auto"))
+		check->mode = CONNECTIVITY_CHECK_AUTO;
+	else if (skip_prefix(arg, "auto=", &cutoff) &&
+		 git_parse_ulong(cutoff, &check->max_commits))
+		check->mode = CONNECTIVITY_CHECK_AUTO;
 	else
 		die(_("unknown --connectivity-check mode '%s'"), arg);
 }

@@ -748,7 +760,9 @@ int cmd_rev_list(int argc,
 	int bisect_find_all = 0;
 	int use_bitmap_index = 0;
 	int filter_provided_objects = 0;
-	struct connectivity_check connectivity_check = { 0 };
+	struct connectivity_check connectivity_check = {
+		.max_commits = INCREMENTAL_MAX_COMMITS,
+	};
 	const char *show_progress = NULL;
 	int ret = 0;
 

@@ -1001,9 +1015,19 @@ int cmd_rev_list(int argc,
 	 * The incremental check would still work, but it would verify
 	 * the whole object graph like the full check, with extra
 	 * per-commit overhead on top, so use the full check.
+	 *
+	 * Otherwise the walk is limited, and revs.commits already holds
+	 * all incoming commits, so counting them for "auto" is cheap.
 	 */
-	if (!revs.limited)
+	if (!revs.limited) {
 		connectivity_check.mode = CONNECTIVITY_CHECK_FULL;
+	} else if (connectivity_check.mode == CONNECTIVITY_CHECK_AUTO) {
+		if (commit_list_count(revs.commits) <=
+		    connectivity_check.max_commits)
+			connectivity_check.mode = CONNECTIVITY_CHECK_INCREMENTAL;
+		else
+			connectivity_check.mode = CONNECTIVITY_CHECK_FULL;
+	}
 
 	if (connectivity_check.mode == CONNECTIVITY_CHECK_INCREMENTAL) {
 		struct commit *commit;

@@ -3,6 +3,7 @@
 #include "gettext.h"
 #include "hex.h"
 #include "odb.h"
+#include "parse.h"
 #include "run-command.h"
 #include "sigchain.h"
 #include "connected.h"

@@ -74,7 +75,8 @@ static void connectivity_check_mode(struct repository *repo,
 				    struct check_connected_options *opt,
 				    struct strbuf *mode)
 {
-	const char *algorithm = NULL;
+	const char *algorithm = NULL, *cutoff;
+	unsigned long max_commits;
 
 	/*
 	 * Deepening fetches do not have the usual boundary of

@@ -93,6 +95,11 @@ static void connectivity_check_mode(struct repository *repo,
 		strbuf_addstr(mode, "full");
 	else if (!strcasecmp(algorithm, "incremental"))
 		strbuf_addstr(mode, "incremental");
+	else if (!strcasecmp(algorithm, "auto"))
+		strbuf_addstr(mode, "auto");
+	else if (skip_iprefix(algorithm, "auto=", &cutoff) &&
+		 git_parse_ulong(cutoff, &max_commits))
+		strbuf_addf(mode, "auto=%lu", max_commits);
 	else {
 		warning(_("unknown transfer.connectivityCheck algorithm '%s', "
 			  "using 'full'"), algorithm);

@@ -725,7 +725,7 @@ test_expect_success 'unknown transfer.connectivityCheck falls back to full' '
 	test_when_finished "rm -rf dst" &&
 	git init --bare dst &&
 	git -C dst fetch ../src base:refs/heads/main &&
-	for value in bogus
+	for value in bogus auto= auto=x
 	do
 		set_connectivity_check dst "$value" &&
 		run_traced git -C dst fetch ../src main &&

@@ -753,7 +753,7 @@ test_expect_success 'fetch uses incremental when configured' '
 	expect_mode incremental
 '
 
-for mode in incremental
+for mode in incremental auto
 do
 	test_expect_success "push with $mode into an empty repository uses full" '
 		test_when_finished "rm -rf dst" &&

@@ -771,4 +771,25 @@ do
 	'
 done
 
+for value in auto auto=1
+do
+	test_expect_success "push with $value uses incremental up to the cutoff" '
+		test_when_finished "rm -rf dst" &&
+		git init --bare dst &&
+		git -C src push ../dst base:refs/heads/main &&
+		set_connectivity_check dst $value &&
+		run_traced git -C src push ../dst main &&
+		expect_mode incremental
+	'
+done
+
+test_expect_success 'push with auto uses full above the cutoff' '
+	test_when_finished "rm -rf dst" &&
+	git init --bare dst &&
+	git -C src push ../dst base:refs/heads/main &&
+	set_connectivity_check dst auto=0 &&
+	run_traced git -C src push ../dst main &&
+	expect_mode full
+'
+
 test_done