fetch: add --[no-]show-forced-updates

Documentation/config/advice.txt

@@ -4,6 +4,10 @@ advice.*::
 	can tell Git that you do not need help by setting these to 'false':
 +
 --
+	fetchShowForcedUpdates::
+		Advice shown when linkgit:git-fetch[1] takes a long time
+		to calculate forced updates after ref updates, or to warn
+		that the check is disabled.
 	pushUpdateRejected::
 		Set this variable to 'false' if you want to disable
 		'pushNonFFCurrent',

Documentation/config/fetch.txt

@@ -63,3 +63,8 @@ fetch.negotiationAlgorithm::
 	Unknown values will cause 'git fetch' to error out.
 +
 See also the `--negotiation-tip` option for linkgit:git-fetch[1].
+
+fetch.showForcedUpdates::
+	Set to false to enable `--no-show-forced-updates` in
+	linkgit:git-fetch[1] and linkgit:git-pull[1] commands.
+	Defaults to true.

Documentation/fetch-options.txt

@@ -221,6 +221,19 @@ endif::git-pull[]
 	When multiple `--server-option=<option>` are given, they are all
 	sent to the other side in the order listed on the command line.
 
+--show-forced-updates::
+	By default, git checks if a branch is force-updated during
+	fetch. This can be disabled through fetch.showForcedUpdates, but
+	the --show-forced-updates option guarantees this check occurs.
+	See linkgit:git-config[1].
+
+--no-show-forced-updates::
+	By default, git checks if a branch is force-updated during
+	fetch. Pass --no-show-forced-updates or set fetch.showForcedUpdates
+	to false to skip this check for performance reasons. If used during
+	'git-pull' the --ff-only option will still check for forced updates
+	before attempting a fast-forward update. See linkgit:git-config[1].
+
 -4::
 --ipv4::
 	Use IPv4 addresses only, ignoring IPv6 addresses.

advice.c

@@ -3,6 +3,7 @@
 #include "color.h"
 #include "help.h"
 
+int advice_fetch_show_forced_updates = 1;
 int advice_push_update_rejected = 1;
 int advice_push_non_ff_current = 1;
 int advice_push_non_ff_matching = 1;
@@ -59,6 +60,7 @@ static struct {
 	const char *name;
 	int *preference;
 } advice_config[] = {
+	{ "fetchShowForcedUpdates", &advice_fetch_show_forced_updates },
 	{ "pushUpdateRejected", &advice_push_update_rejected },
 	{ "pushNonFFCurrent", &advice_push_non_ff_current },
 	{ "pushNonFFMatching", &advice_push_non_ff_matching },

advice.h

@@ -3,6 +3,7 @@
 
 #include "git-compat-util.h"
 
+extern int advice_fetch_show_forced_updates;
 extern int advice_push_update_rejected;
 extern int advice_push_non_ff_current;
 extern int advice_push_non_ff_matching;

builtin/fetch.c

@@ -24,6 +24,8 @@
 #include "list-objects-filter-options.h"
 #include "commit-reach.h"
 
+#define FORCED_UPDATES_DELAY_WARNING_IN_MS (10 * 1000)
+
 static const char * const builtin_fetch_usage[] = {
 	N_("git fetch [<options>] [<repository> [<refspec>...]]"),
 	N_("git fetch [<options>] <group>"),
@@ -39,6 +41,8 @@ enum {
 };
 
 static int fetch_prune_config = -1; /* unspecified */
+static int fetch_show_forced_updates = 1;
+static uint64_t forced_updates_ms = 0;
 static int prune = -1; /* unspecified */
 #define PRUNE_BY_DEFAULT 0 /* do we prune by default? */
 
@@ -79,6 +83,11 @@ static int git_fetch_config(const char *k, const char *v, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(k, "fetch.showforcedupdates")) {
+		fetch_show_forced_updates = git_config_bool(k, v);
+		return 0;
+	}
+
 	if (!strcmp(k, "submodule.recurse")) {
 		int r = git_config_bool(k, v) ?
 			RECURSE_SUBMODULES_ON : RECURSE_SUBMODULES_OFF;
@@ -169,6 +178,8 @@ static struct option builtin_fetch_options[] = {
 	OPT_STRING_LIST(0, "negotiation-tip", &negotiation_tip, N_("revision"),
 			N_("report that we have only objects reachable from this object")),
 	OPT_PARSE_LIST_OBJECTS_FILTER(&filter_options),
+	OPT_BOOL(0, "show-forced-updates", &fetch_show_forced_updates,
+		 N_("check for forced-updates on all updated branches")),
 	OPT_END()
 };
 
@@ -699,6 +710,7 @@ static int update_local_ref(struct ref *ref,
 	enum object_type type;
 	struct branch *current_branch = branch_get(NULL);
 	const char *pretty_ref = prettify_refname(ref->name);
+	int fast_forward = 0;
 
 	type = oid_object_info(the_repository, &ref->new_oid, NULL);
 	if (type < 0)
@@ -773,9 +785,18 @@ static int update_local_ref(struct ref *ref,
 		return r;
 	}
 
-	if (in_merge_bases(current, updated)) {
+	if (fetch_show_forced_updates) {
+		uint64_t t_before = getnanotime();
+		fast_forward = in_merge_bases(current, updated);
+		forced_updates_ms += (getnanotime() - t_before) / 1000000;
+	} else {
+		fast_forward = 1;
+	}
+
+	if (fast_forward) {
 		struct strbuf quickref = STRBUF_INIT;
 		int r;
+
 		strbuf_add_unique_abbrev(&quickref, &current->object.oid, DEFAULT_ABBREV);
 		strbuf_addstr(&quickref, "..");
 		strbuf_add_unique_abbrev(&quickref, &ref->new_oid, DEFAULT_ABBREV);
@@ -971,6 +992,17 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 		      " 'git remote prune %s' to remove any old, conflicting "
 		      "branches"), remote_name);
 
+	if (advice_fetch_show_forced_updates) {
+		if (!fetch_show_forced_updates) {
+			warning(_("Fetch normally indicates which branches had a forced update, but that check has been disabled."));
+			warning(_("To re-enable, use '--show-forced-updates' flag or run 'git config fetch.showForcedUpdates true'."));
+		} else if (forced_updates_ms > FORCED_UPDATES_DELAY_WARNING_IN_MS) {
+			warning(_("It took %.2f seconds to check forced updates. You can use '--no-show-forced-updates'\n"),
+				forced_updates_ms / 1000.0);
+			warning(_("or run 'git config fetch.showForcedUpdates false' to avoid this check.\n"));
+		}
+	}
+
  abort:
 	strbuf_release(&note);
 	free(url);

builtin/pull.c

@@ -128,6 +128,7 @@ static char *opt_update_shallow;
 static char *opt_refmap;
 static char *opt_ipv4;
 static char *opt_ipv6;
+static int opt_show_forced_updates = -1;
 
 static struct option pull_options[] = {
 	/* Shared options */
@@ -240,6 +241,8 @@ static struct option pull_options[] = {
 	OPT_PASSTHRU('6',  "ipv6", &opt_ipv6, NULL,
 		N_("use IPv6 addresses only"),
 		PARSE_OPT_NOARG),
+	OPT_BOOL(0, "show-forced-updates", &opt_show_forced_updates,
+		 N_("check for forced-updates on all updated branches")),
 
 	OPT_END()
 };
@@ -549,6 +552,10 @@ static int run_fetch(const char *repo, const char **refspecs)
 		argv_array_push(&args, opt_ipv4);
 	if (opt_ipv6)
 		argv_array_push(&args, opt_ipv6);
+	if (opt_show_forced_updates > 0)
+		argv_array_push(&args, "--show-forced-updates");
+	else if (opt_show_forced_updates == 0)
+		argv_array_push(&args, "--no-show-forced-updates");
 
 	if (repo) {
 		argv_array_push(&args, repo);

t/t5510-fetch.sh

@@ -978,4 +978,27 @@ test_expect_success '--negotiation-tip limits "have" lines sent with HTTP protoc
 	check_negotiation_tip
 '
 
+test_expect_success '--no-show-forced-updates' '
+	mkdir forced-updates &&
+	(
+		cd forced-updates &&
+		git init &&
+		test_commit 1 &&
+		test_commit 2
+	) &&
+	git clone forced-updates forced-update-clone &&
+	git clone forced-updates no-forced-update-clone &&
+	git -C forced-updates reset --hard HEAD~1 &&
+	(
+		cd forced-update-clone &&
+		git fetch --show-forced-updates origin 2>output &&
+		test_i18ngrep "(forced update)" output
+	) &&
+	(
+		cd no-forced-update-clone &&
+		git fetch --no-show-forced-updates origin 2>output &&
+		! test_i18ngrep "(forced update)" output
+	)
+'
+
 test_done