Documentation/config/fetch.adoc, builtin/fetch.c, t/t5537-fetch-shallow.sh

diff --git a/Documentation/config/fetch.adoc b/Documentation/config/fetch.adoc
index 00435e9a16..e63e54a463 100644
--- a/Documentation/config/fetch.adoc
+++ b/Documentation/config/fetch.adoc
@@ -145,3 +145,18 @@ remove the value for the `fetch.bundleCreationToken` value before fetching.
 `never`;;
 	Never create or modify the `remotes/<name>/HEAD` symbolic-ref.
 --
+
+`fetch.shallow`::
+	If true, and the repository is a shallow repository (see
+	linkgit:git-clone[1] `--depth`), a fetch or `git pull` that names no
+	explicit refspec and would otherwise fall back to the remote's
+	configured `remote.<name>.fetch` refspec instead fetches only the
+	current branch's upstream, when that upstream is on the remote being
+	fetched. This avoids negotiating history for every branch the remote
+	advertises, which can be slow on a shallow repository that tracks
+	many disjoint shallow histories. It has no effect on a fetch that
+	names an explicit remote or refspec, and no effect on a repository
+	that is not shallow. Defaults to false.
++
+`remotes/<name>/HEAD` is still kept up to date per `fetch.followRemoteHEAD`
+while this is in effect, only the other branches are skipped.
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 533fdfe7d8..b22f7fe5f4 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -111,6 +111,7 @@ struct fetch_config {
 	int recurse_submodules;
 	int parallel;
 	int submodule_fetch_jobs;
+	int shallow;
 };
 
 static int git_fetch_config(const char *k, const char *v,
@@ -175,6 +176,11 @@ static int git_fetch_config(const char *k, const char *v,
 		return 0;
 	}
 
+	if (!strcmp(k, "fetch.shallow")) {
+		fetch_config->shallow = git_config_bool(k, v);
+		return 0;
+	}
+
 	if (!strcmp(k, "fetch.followremotehead")) {
 		if (!v)
 			return config_error_nonbool(k);
@@ -1958,15 +1964,19 @@ static int do_fetch(struct transport *transport,
 		refspec_ref_prefixes(rs, &transport_ls_refs_options.ref_prefixes);
 	} else {
 		struct branch *branch = branch_get(NULL);
+		int tracks_this_remote = branch && branch_has_merge_config(branch) &&
+			!strcmp(branch->remote_name, transport->remote->name);
+		int narrow_to_tracked_ref = config->shallow &&
+			is_repository_shallow(the_repository) && tracks_this_remote;
 
 		if (transport->remote->fetch.nr) {
-			refspec_ref_prefixes(&transport->remote->fetch,
-					     &transport_ls_refs_options.ref_prefixes);
+			if (!narrow_to_tracked_ref)
+				refspec_ref_prefixes(&transport->remote->fetch,
+						     &transport_ls_refs_options.ref_prefixes);
 			if (follow_remote_head != FOLLOW_REMOTE_NEVER)
 				do_set_head = 1;
 		}
-		if (branch && branch_has_merge_config(branch) &&
-		    !strcmp(branch->remote_name, transport->remote->name)) {
+		if (tracks_this_remote) {
 			int i;
 			for (i = 0; i < branch->merge_nr; i++) {
 				strvec_push(&transport_ls_refs_options.ref_prefixes,
diff --git a/t/t5537-fetch-shallow.sh b/t/t5537-fetch-shallow.sh
index f323ceebd2..8143af9fc3 100755
--- a/t/t5537-fetch-shallow.sh
+++ b/t/t5537-fetch-shallow.sh
@@ -13,6 +13,24 @@ commit() {
 	git commit -m "$1"
 }
 
+check_upstream_refs () {
+	git for-each-ref --format="%(refname)" refs/remotes/upstream/ >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+check_upstream_head () {
+	git symbolic-ref refs/remotes/upstream/HEAD >actual &&
+	echo "refs/remotes/upstream/$1" >expect &&
+	test_cmp expect actual
+}
+
+check_same_tip () {
+	git log --oneline -1 "$1" >expect &&
+	git -C "$2" log --oneline -1 "$3" >actual &&
+	test_cmp expect actual
+}
+
 test_expect_success 'setup' '
 	commit 1 &&
 	commit 2 &&
@@ -261,6 +279,134 @@ test_expect_success 'fetch --deepen does not truncate' '
 	test_cmp expect actual
 '
 
+test_expect_success 'fetch.shallow setup' '
+	git branch narrow-side &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		.git narrow-default &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		.git narrow-enabled &&
+	(
+		cd narrow-default &&
+		git remote add upstream ../.git &&
+		git fetch --depth=1 upstream main:refs/remotes/upstream/main &&
+		git branch --set-upstream-to=upstream/main main
+	) &&
+	(
+		cd narrow-enabled &&
+		git remote add upstream ../.git &&
+		git fetch --depth=1 upstream main:refs/remotes/upstream/main &&
+		git branch --set-upstream-to=upstream/main main &&
+		git config fetch.shallow true
+	)
+'
+
+test_expect_success 'a refspec-less fetch expands to the configured refspec by default' '
+	(
+		cd narrow-default &&
+		git fetch upstream &&
+		check_upstream_refs <<-\EOF
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/narrow-side
+		EOF
+	)
+'
+
+test_expect_success 'fetch.shallow=true limits a refspec-less fetch to the tracked branch' '
+	(
+		cd narrow-enabled &&
+		git fetch upstream &&
+		check_upstream_refs <<-\EOF
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		EOF
+	)
+'
+
+test_expect_success 'fetch.shallow=true still creates refs/remotes/<remote>/HEAD' '
+	(
+		cd narrow-enabled &&
+		git symbolic-ref -d refs/remotes/upstream/HEAD &&
+		git fetch upstream &&
+		check_upstream_head main
+	)
+'
+
+test_expect_success 'fetch.shallow=true with followRemoteHEAD=always corrects a stale HEAD' '
+	test_when_finished \
+		"git -C narrow-enabled update-ref -d refs/remotes/upstream/stale-branch" &&
+	(
+		cd narrow-enabled &&
+		git update-ref refs/remotes/upstream/stale-branch refs/remotes/upstream/main &&
+		git symbolic-ref refs/remotes/upstream/HEAD refs/remotes/upstream/stale-branch &&
+		git -c fetch.followRemoteHEAD=always fetch upstream &&
+		check_upstream_head main
+	)
+'
+
+test_expect_success 'fetch.shallow=true still updates the tracked branch' '
+	commit 5 &&
+	git -C narrow-enabled fetch upstream &&
+	check_same_tip main narrow-enabled refs/remotes/upstream/main
+'
+
+test_expect_success 'fetch.shallow=true keeps git pull narrowed too' '
+	test_when_finished "git branch -D narrow-side" &&
+	commit 6 &&
+	(
+		cd narrow-enabled &&
+		git pull &&
+		check_upstream_refs <<-\EOF
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		EOF
+	) &&
+	check_same_tip main narrow-enabled HEAD
+'
+
+test_expect_success 'fetch.shallow=true has no effect on a non-shallow repository' '
+	git clone --no-local --branch main --single-branch .git narrow-full &&
+	(
+		cd narrow-full &&
+		git rev-parse --is-shallow-repository >actual &&
+		echo false >expect &&
+		test_cmp expect actual &&
+		git remote add upstream ../.git &&
+		git fetch upstream &&
+		git branch --set-upstream-to=upstream/main main &&
+		git config fetch.shallow true
+	) &&
+	test_when_finished "git branch -D narrow-full-side" &&
+	git branch narrow-full-side &&
+	(
+		cd narrow-full &&
+		git fetch upstream &&
+		check_upstream_refs <<-\EOF
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/narrow-full-side
+		EOF
+	)
+'
+
+test_expect_success 'fetch.shallow=true only narrows a fetch of the tracked remote' '
+	test_when_finished "git branch -D other-side" &&
+	git branch other-side &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		.git narrow-other-remote &&
+	(
+		cd narrow-other-remote &&
+		git remote add upstream ../.git &&
+		git config fetch.shallow true &&
+		git fetch upstream &&
+		check_upstream_refs <<-\EOF
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/other-side
+		EOF
+	)
+'
+
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd
 

base-commit: d38352cd43ab9745686d697872408bc3249a153f

Documentation/git-remote.adoc, Documentation/pull-fetch-param.adoc, builtin/fetch.c, builtin/remote.c, refspec.c, refspec.h, remote.c, remote.h, t/meson.build, t/t5505-remote.sh, t/t5585-fetch-tracking-refspec.sh

diff --git a/Documentation/git-remote.adoc b/Documentation/git-remote.adoc
index eaae30aa88..7856ccf54f 100644
--- a/Documentation/git-remote.adoc
+++ b/Documentation/git-remote.adoc
@@ -52,6 +52,13 @@ Add a remote named _<name>_ for the repository at
 _<URL>_.  The command `git fetch <name>` can then be used to create and
 update remote-tracking branches `<name>/<branch>`.
 +
+If the repository is already a shallow repository (see linkgit:git-clone[1]
+`--depth`) and neither `-t` nor `--mirror` is given, the remote is set up
+with the special tracking refspec (see the _<refspec>_ entry in
+linkgit:git-fetch[1]) instead of the default glob refspec, so that
+`git fetch <name>` does not need to negotiate history for every branch
+the remote has.
++
 With `-f` option, `git fetch <name>` is run immediately after
 the remote information is set up.
 +
diff --git a/Documentation/pull-fetch-param.adoc b/Documentation/pull-fetch-param.adoc
index d903dc8900..e1a42152d9 100644
--- a/Documentation/pull-fetch-param.adoc
+++ b/Documentation/pull-fetch-param.adoc
@@ -48,6 +48,16 @@ Negative refspecs can themselves be pattern refspecs. However, they may only
 contain a _<src>_ and do not specify a _<dst>_. Fully spelled out hex object
 names are also not supported.
 +
+The special refspec `:` (or `+:` to allow non-fast-forward updates)
+directs Git to fetch whichever branches at the remote our local branches
+have as their `@{upstream}`, plus the remote's default branch, which is
+always included so that it is available even before anything is set up
+to track it. Unlike the same syntax when pushing, the local branch name
+plays no role here beyond identifying which remote branch to fetch: the
+result is written to `refs/remotes/<remote>/<branch>` using the remote's
+own branch name, and several local branches built on the same remote
+branch only cause it to be fetched once.
++
 `tag <tag>` means the same as `refs/tags/<tag>:refs/tags/<tag>`;
 it requests fetching everything up to the given tag.
 +
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 533fdfe7d8..7a3387d733 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -500,10 +500,55 @@ static void filter_prefetch_refspec(struct refspec *rs)
 	}
 }
 
+static void fetch_tracked_branches(struct remote *remote,
+				   const struct ref *remote_refs,
+				   struct ref ***tail,
+				   char **default_branch_out,
+				   int force)
+{
+	struct string_list tracked = STRING_LIST_INIT_DUP;
+	struct string_list_item *item;
+	struct ref *head;
+	char *default_branch = NULL;
+
+	branches_tracking_remote(remote, &tracked);
+
+	head = get_remote_ref(remote_refs, "HEAD");
+	if (head && head->symref && *head->symref) {
+		default_branch = xstrdup(head->symref);
+		string_list_insert(&tracked, default_branch);
+	}
+	free_one_ref(head);
+
+	for_each_string_list_item(item, &tracked) {
+		struct refspec_item ref = { .force = force };
+		const char *branch_name = item->string;
+		int is_default_branch = default_branch &&
+			!strcmp(item->string, default_branch);
+
+		skip_prefix(branch_name, "refs/heads/", &branch_name);
+		ref.src = xstrdup(is_default_branch ? "HEAD" : item->string);
+		ref.dst = xstrfmt("refs/remotes/%s/%s", remote->name, branch_name);
+		get_fetch_map(remote_refs, &ref, tail, 1);
+		free(ref.src);
+		free(ref.dst);
+	}
+
+	if (default_branch && default_branch_out) {
+		const char *branch_name = default_branch;
+		skip_prefix(branch_name, "refs/heads/", &branch_name);
+		*default_branch_out = xstrdup(branch_name);
+	}
+
+	free(default_branch);
+	string_list_clear(&tracked, 0);
+}
+
 static struct ref *get_ref_map(struct remote *remote,
 			       const struct ref *remote_refs,
 			       struct refspec *rs,
-			       int tags, int *autotags)
+			       int tags, int *autotags,
+			       char **bootstrap_head_branch)
 {
 	int i;
 	struct ref *rm;
@@ -570,6 +615,12 @@ static struct ref *get_ref_map(struct remote *remote,
 		     /* Note: has_merge implies non-NULL branch->remote_name */
 		     (has_merge && !strcmp(branch->remote_name, remote->name)))) {
 			for (i = 0; i < remote->fetch.nr; i++) {
+				if (remote->fetch.items[i].tracking) {
+					fetch_tracked_branches(remote, remote_refs, &tail,
+								bootstrap_head_branch,
+								remote->fetch.items[i].force);
+					continue;
+				}
 				get_fetch_map(remote_refs, &remote->fetch.items[i], &tail, 0);
 				if (remote->fetch.items[i].dst &&
 				    remote->fetch.items[i].dst[0])
@@ -1751,14 +1802,14 @@ static void warn_set_head(const char *remote, const char *head_name,
 }
 
 static int set_head(const struct ref *remote_refs, struct remote *remote,
-			int follow_remote_head)
+			int follow_remote_head, const char *known_head_branch)
 {
 	int result = 0, create_only, baremirror, was_detached;
 	struct strbuf b_head = STRBUF_INIT, b_remote_head = STRBUF_INIT,
 		      b_local_head = STRBUF_INIT;
 	const char *no_warn_branch = remote->no_warn_branch;
 	char *head_name = NULL;
-	struct ref *ref, *matches;
+	struct ref *ref, *matches = NULL;
 	struct ref *fetch_map = NULL, **fetch_map_tail = &fetch_map;
 	struct refspec_item refspec = {
 		.force = 0,
@@ -1769,19 +1820,23 @@ static int set_head(const struct ref *remote_refs, struct remote *remote,
 	struct string_list heads = STRING_LIST_INIT_DUP;
 	struct ref_store *refs = get_main_ref_store(the_repository);
 
-	get_fetch_map(remote_refs, &refspec, &fetch_map_tail, 0);
-	matches = guess_remote_head(find_ref_by_name(remote_refs, "HEAD"),
-				    fetch_map, REMOTE_GUESS_HEAD_ALL);
-	for (ref = matches; ref; ref = ref->next) {
-		string_list_append(&heads, strip_refshead(ref->name));
-	}
+	if (known_head_branch) {
+		head_name = xstrdup(known_head_branch);
+	} else {
+		get_fetch_map(remote_refs, &refspec, &fetch_map_tail, 0);
+		matches = guess_remote_head(find_ref_by_name(remote_refs, "HEAD"),
+					    fetch_map, REMOTE_GUESS_HEAD_ALL);
+		for (ref = matches; ref; ref = ref->next) {
+			string_list_append(&heads, strip_refshead(ref->name));
+		}
 
-	if (!heads.nr)
-		result = 1;
-	else if (heads.nr > 1)
-		result = 1;
-	else
-		head_name = xstrdup(heads.items[0].string);
+		if (!heads.nr)
+			result = 1;
+		else if (heads.nr > 1)
+			result = 1;
+		else
+			head_name = xstrdup(heads.items[0].string);
+	}
 
 	if (!head_name)
 		goto cleanup;
@@ -1923,6 +1978,7 @@ static int do_fetch(struct transport *transport,
 	struct strmap rejected_refs = STRMAP_INIT;
 	int summary_width = 0;
 	int follow_remote_head;
+	char *bootstrap_head_branch = NULL;
 
 	if (tags == TAGS_DEFAULT) {
 		if (transport->remote->fetch_tags == 2)
@@ -1958,15 +2014,29 @@ static int do_fetch(struct transport *transport,
 		refspec_ref_prefixes(rs, &transport_ls_refs_options.ref_prefixes);
 	} else {
 		struct branch *branch = branch_get(NULL);
+		int tracks_this_remote = branch && branch_has_merge_config(branch) &&
+			!strcmp(branch->remote_name, transport->remote->name);
+		int tracking_refspec = transport->remote->fetch.nr == 1 &&
+			transport->remote->fetch.items[0].tracking;
 
-		if (transport->remote->fetch.nr) {
+		if (tracking_refspec) {
+			struct string_list tracked = STRING_LIST_INIT_DUP;
+			struct string_list_item *item;
+
+			branches_tracking_remote(transport->remote, &tracked);
+			for_each_string_list_item(item, &tracked)
+				strvec_push(&transport_ls_refs_options.ref_prefixes,
+					    item->string);
+			string_list_clear(&tracked, 0);
+			strvec_push(&transport_ls_refs_options.ref_prefixes, "HEAD");
+		} else if (transport->remote->fetch.nr) {
 			refspec_ref_prefixes(&transport->remote->fetch,
 					     &transport_ls_refs_options.ref_prefixes);
-			if (follow_remote_head != FOLLOW_REMOTE_NEVER)
-				do_set_head = 1;
 		}
-		if (branch && branch_has_merge_config(branch) &&
-		    !strcmp(branch->remote_name, transport->remote->name)) {
+		if (transport->remote->fetch.nr &&
+		    follow_remote_head != FOLLOW_REMOTE_NEVER)
+			do_set_head = 1;
+		if (tracks_this_remote) {
 			int i;
 			for (i = 0; i < branch->merge_nr; i++) {
 				strvec_push(&transport_ls_refs_options.ref_prefixes,
@@ -2006,7 +2076,8 @@ static int do_fetch(struct transport *transport,
 	transport_ls_refs_options_release(&transport_ls_refs_options);
 
 	ref_map = get_ref_map(transport->remote, remote_refs, rs,
-			      tags, &autotags);
+			      tags, &autotags, &bootstrap_head_branch);
+
 	if (!update_head_ok)
 		check_not_current_branch(ref_map);
 
@@ -2169,10 +2240,12 @@ static int do_fetch(struct transport *transport,
 		 * Way too many cases where this can go wrong so let's just
 		 * ignore errors and fail silently for now.
 		 */
-		set_head(remote_refs, transport->remote, follow_remote_head);
+		set_head(remote_refs, transport->remote, follow_remote_head,
+			 bootstrap_head_branch);
 	}
 
 cleanup:
+	free(bootstrap_head_branch);
 	/*
 	 * When using batched updates, we want to commit the non-rejected
 	 * updates and also handle the rejections.
diff --git a/builtin/remote.c b/builtin/remote.c
index de989ea3ba..e407d67037 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -16,6 +16,7 @@
 #include "rebase.h"
 #include "refs.h"
 #include "refspec.h"
+#include "shallow.h"
 #include "odb.h"
 #include "strvec.h"
 #include "commit-reach.h"
@@ -127,13 +128,17 @@ static void add_branch(const char *key, const char *branchname,
 		       const char *remotename, int mirror, struct strbuf *tmp)
 {
 	strbuf_reset(tmp);
-	strbuf_addch(tmp, '+');
-	if (mirror)
-		strbuf_addf(tmp, "refs/%s:refs/%s",
-				branchname, branchname);
-	else
-		strbuf_addf(tmp, "refs/heads/%s:refs/remotes/%s/%s",
-				branchname, remotename, branchname);
+	if (!strcmp(branchname, ":")) {
+		strbuf_addstr(tmp, "+:");
+	} else {
+		strbuf_addch(tmp, '+');
+		if (mirror)
+			strbuf_addf(tmp, "refs/%s:refs/%s",
+					branchname, branchname);
+		else
+			strbuf_addf(tmp, "refs/heads/%s:refs/remotes/%s/%s",
+					branchname, remotename, branchname);
+	}
 	repo_config_set_multivar(the_repository, key, tmp->buf, "^$", 0);
 }
 
@@ -233,11 +238,13 @@ static int add(int argc, const char **argv, const char *prefix,
 		strbuf_reset(&buf);
 		strbuf_addf(&buf, "remote.%s.fetch", name);
 		if (track.nr == 0)
-			string_list_append(&track, "*");
-		for (size_t i = 0; i < track.nr; i++) {
+			string_list_append(&track,
+				mirror == MIRROR_NONE &&
+				is_repository_shallow(the_repository) ?
+				":" : "*");
+		for (size_t i = 0; i < track.nr; i++)
 			add_branch(buf.buf, track.items[i].string,
 				   name, mirror, &buf2);
-		}
 	}
 
 	if (mirror & MIRROR_PUSH) {
diff --git a/refspec.c b/refspec.c
index 7cb479983b..84a19b5b5c 100644
--- a/refspec.c
+++ b/refspec.c
@@ -49,6 +49,11 @@ static int parse_refspec(struct refspec_item *item, const char *refspec,
 		return 1;
 	}
 
+	if (fetch && rhs == lhs && rhs[1] == '\0') {
+		item->tracking = 1;
+		return 1;
+	}
+
 	if (rhs) {
 		size_t rlen = strlen(++rhs);
 		is_glob = (1 <= rlen && strchr(rhs, '*'));
@@ -181,6 +186,7 @@ void refspec_item_clear(struct refspec_item *item)
 	item->force = 0;
 	item->pattern = 0;
 	item->matching = 0;
+	item->tracking = 0;
 	item->exact_sha1 = 0;
 }
 
@@ -373,7 +379,7 @@ static int refspec_find_negative_match(struct refspec *rs, struct refspec_item *
 		struct refspec_item *refspec = &rs->items[i];
 		char *expn_name;
 
-		if (refspec->negative)
+		if (refspec->negative || refspec->tracking)
 			continue;
 
 		/* Note the reversal of src and dst */
diff --git a/refspec.h b/refspec.h
index fadef67933..97bd6ffef5 100644
--- a/refspec.h
+++ b/refspec.h
@@ -27,6 +27,7 @@ struct refspec_item {
 	unsigned matching : 1;
 	unsigned exact_sha1 : 1;
 	unsigned negative : 1;
+	unsigned tracking : 1;
 
 	char *src;
 	char *dst;
diff --git a/remote.c b/remote.c
index fe62068463..53b410f7e7 100644
--- a/remote.c
+++ b/remote.c
@@ -988,6 +988,29 @@ void ref_push_report_free(struct ref_push_report *report)
 
 int remote_find_tracking(struct remote *remote, struct refspec_item *refspec)
 {
+	if (remote->fetch.nr == 1 && remote->fetch.items[0].tracking) {
+		struct strbuf prefix = STRBUF_INIT;
+		const char *branch_name;
+		int ret = -1;
+
+		strbuf_addf(&prefix, "refs/remotes/%s/", remote->name);
+		if (!refspec->src) {
+			if (refspec->dst &&
+			    skip_prefix(refspec->dst, prefix.buf, &branch_name)) {
+				refspec->src = xstrfmt("refs/heads/%s", branch_name);
+				refspec->force = 1;
+				ret = 0;
+			}
+		} else if (skip_prefix(refspec->src, "refs/heads/", &branch_name)) {
+			free(refspec->dst);
+			refspec->dst = xstrfmt("%s%s", prefix.buf, branch_name);
+			refspec->force = 1;
+			ret = 0;
+		}
+		strbuf_release(&prefix);
+		return ret;
+	}
+
 	return refspec_find_match(&remote->fetch, refspec);
 }
 
@@ -1874,6 +1897,35 @@ int branch_merge_matches(struct branch *branch,
 	return refname_match(branch->merge[i]->src, refname);
 }
 
+struct branches_tracking_remote_cb_data {
+	struct remote *remote;
+	struct string_list *tracked;
+};
+
+static int add_if_tracking_remote(const struct reference *ref, void *cb_data)
+{
+	struct branches_tracking_remote_cb_data *data = cb_data;
+	struct branch *branch;
+
+	branch = branch_get(ref->name);
+	if (!branch_has_merge_config(branch) ||
+	    strcmp(branch->remote_name, data->remote->name))
+		return 0;
+
+	for (int i = 0; i < branch->merge_nr; i++)
+		string_list_insert(data->tracked, branch->merge[i]->src);
+
+	return 0;
+}
+
+void branches_tracking_remote(struct remote *remote, struct string_list *tracked)
+{
+	struct branches_tracking_remote_cb_data data = { remote, tracked };
+
+	refs_for_each_branch_ref(get_main_ref_store(the_repository),
+				  add_if_tracking_remote, &data);
+}
+
 __attribute__((format (printf,2,3)))
 static char *error_buf(struct strbuf *err, const char *fmt, ...)
 {
@@ -2138,7 +2190,7 @@ int get_fetch_map(const struct ref *remote_refs,
 {
 	struct ref *ref_map, **rmp;
 
-	if (refspec->negative)
+	if (refspec->negative || refspec->tracking)
 		return 0;
 
 	if (refspec->pattern) {
diff --git a/remote.h b/remote.h
index cca02033b9..5ab187e00a 100644
--- a/remote.h
+++ b/remote.h
@@ -353,6 +353,9 @@ int branch_has_merge_config(struct branch *branch);
 
 int branch_merge_matches(struct branch *, int n, const char *);
 
+/* fills tracked with the refname of every local branch's upstream on remote */
+void branches_tracking_remote(struct remote *remote, struct string_list *tracked);
+
 /* list of the remote in a group as configured */
 struct remote_group_data {
 	const char *name;
diff --git a/t/meson.build b/t/meson.build
index 3ca7b27104..4c13048d46 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -728,6 +728,7 @@ integration_tests = [
   't5582-fetch-negative-refspec.sh',
   't5583-push-branches.sh',
   't5584-http-429-retry.sh',
+  't5585-fetch-tracking-refspec.sh',
   't5600-clone-fail-cleanup.sh',
   't5601-clone.sh',
   't5602-clone-remote-exec.sh',
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 5fbfcb0848..f7c3857098 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -137,6 +137,50 @@ test_expect_success 'filters are listed by git remote -v only' '
 	test_grep ! "\[blob:none\]" out
 '
 
+test_expect_success 'add remote -t keeps an explicit refspec in a shallow repository' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add -t main upstream ../two &&
+		test_cmp_config "+refs/heads/main:refs/remotes/upstream/main" \
+			remote.upstream.fetch
+	)
+'
+
+test_expect_success 'add remote keeps the wildcard refspec in a full repository' '
+	test_when_finished "rm -rf full-add" &&
+	git clone --no-local one full-add &&
+	(
+		cd full-add &&
+		git remote add upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.fetch
+	)
+'
+
+test_expect_success 'a remote added in a shallow repository defaults to the tracking refspec' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add upstream ../two &&
+		test_cmp_config "+:" remote.upstream.fetch &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		EOF
+		test_cmp expect actual &&
+		git branch --set-upstream-to=upstream &&
+		test_cmp_config upstream branch.main.remote &&
+		test_cmp_config refs/heads/main branch.main.merge
+	)
+'
+
 test_expect_success 'check remote-tracking' '
 	(
 		cd test &&
diff --git a/t/t5585-fetch-tracking-refspec.sh b/t/t5585-fetch-tracking-refspec.sh
new file mode 100755
index 0000000000..ebc3c5787f
--- /dev/null
+++ b/t/t5585-fetch-tracking-refspec.sh
@@ -0,0 +1,124 @@
+#!/bin/sh
+
+test_description='"git fetch" with the tracking refspec ":" (or "+:")
+
+The special refspec fetches whichever branches at the remote our local
+branches have as their @{upstream}, plus the default branch of that
+remote, which is always included so that it is available even before
+anything is set up to track it. git remote add uses it by default for
+a new remote in an already shallow repository, so that adding a
+second remote there does not turn the next plain fetch or pull into
+one that negotiates history for every branch the remote has.
+'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit main-1 &&
+	test_commit main-2 &&
+	git checkout -b side main-1 &&
+	test_commit side-1 &&
+	git checkout -b next main-1 &&
+	test_commit next-1 &&
+	git checkout main
+'
+
+test_expect_success 'clone shallow and single-branch, then add a second remote' '
+	git clone --no-local --depth=1 --branch main --single-branch . client &&
+	(
+		cd client &&
+		git remote add upstream .. &&
+		test_cmp_config "+:" remote.upstream.fetch
+	)
+'
+
+test_expect_success 'fetching the new remote does not need every branch it has' '
+	(
+		cd client &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'set-upstream-to now resolves right after that first fetch' '
+	(
+		cd client &&
+		git branch --set-upstream-to=upstream &&
+		test_cmp_config upstream branch.main.remote &&
+		test_cmp_config refs/heads/main branch.main.merge
+	)
+'
+
+test_expect_success 'a branch checked out from a one-time fetch is kept updated by later plain fetches' '
+	(
+		cd client &&
+		git fetch upstream side:refs/remotes/upstream/side &&
+		git branch side-topic upstream/side
+	) &&
+	git checkout side &&
+	test_commit side-2 &&
+	git checkout main &&
+	(
+		cd client &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual &&
+		git rev-parse refs/remotes/upstream/side >actual-oid &&
+		git -C .. rev-parse side >expect-oid &&
+		test_cmp expect-oid actual-oid
+	)
+'
+
+test_expect_success 'a second branch tracking the same upstream branch does not fetch it twice' '
+	(
+		cd client &&
+		git branch side-topic-2 upstream/side &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'a branch tracking a different remote is not fetched from upstream' '
+	(
+		cd client &&
+		git remote add other .. &&
+		git fetch other next:refs/remotes/other/next &&
+		git branch next-topic other/next &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'git remote show does not choke on the tracking refspec' '
+	(
+		cd client &&
+		git remote show upstream
+	)
+'
+
+test_done

base-commit: 3bc0341126508f78f5869cbfc0005e987efdf0c7

Documentation/config/remote.adoc, Documentation/fetch-options.adoc, builtin/fetch.c, remote.c, remote.h, t/t5510-fetch.sh

diff --git a/Documentation/config/remote.adoc b/Documentation/config/remote.adoc
index 3a20d0f752..00f9ed8d3d 100644
--- a/Documentation/config/remote.adoc
+++ b/Documentation/config/remote.adoc
@@ -33,6 +33,12 @@ remote.<name>.fetch::
 	The default set of "refspec" for linkgit:git-fetch[1]. See
 	linkgit:git-fetch[1].
 
+remote.<name>.refmap::
+	The default value of the `--refmap` option for linkgit:git-fetch[1].
+	Only takes effect when the fetch names what to fetch explicitly,
+	either on the command line or via `remote.<name>.fetch`. See the
+	`--refmap` entry in linkgit:git-fetch[1].
+
 remote.<name>.push::
 	The default set of "refspec" for linkgit:git-push[1]. See
 	linkgit:git-push[1].
diff --git a/Documentation/fetch-options.adoc b/Documentation/fetch-options.adoc
index 035f780e58..538914bc6e 100644
--- a/Documentation/fetch-options.adoc
+++ b/Documentation/fetch-options.adoc
@@ -244,6 +244,9 @@ endif::git-pull[]
 	refspecs and rely entirely on the refspecs supplied as
 	command-line arguments. See section on "Configured Remote-tracking
 	Branches" for details.
++
+`remote.<name>.refmap` provides the default value for this option, the
+same way `remote.<name>.fetch` provides the default refspecs to fetch.
 
 `-t`::
 `--tags`::
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 533fdfe7d8..7651b41139 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -509,6 +509,8 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct ref *rm;
 	struct ref *ref_map = NULL;
 	struct ref **tail = &ref_map;
+	struct refspec *effective_refmap =
+		refmap.nr ? &refmap : remote ? &remote->refmap : NULL;
 
 	/* opportunistically-updated references: */
 	struct ref *orefs = NULL, **oref_tail = &orefs;
@@ -552,14 +554,14 @@ static struct ref *get_ref_map(struct remote *remote,
 		 * by ref_remove_duplicates() in favor of one of these
 		 * opportunistic entries with FETCH_HEAD_IGNORE.
 		 */
-		if (refmap.nr)
-			fetch_refspec = &refmap;
+		if (effective_refmap && effective_refmap->nr)
+			fetch_refspec = effective_refmap;
 		else
 			fetch_refspec = &remote->fetch;
 
 		for (i = 0; i < fetch_refspec->nr; i++)
 			get_fetch_map(ref_map, &fetch_refspec->items[i], &oref_tail, 1);
-	} else if (refmap.nr) {
+	} else if (effective_refmap && effective_refmap->nr) {
 		die("--refmap option is only meaningful with command-line refspec(s)");
 	} else {
 		/* Use the defaults */
diff --git a/remote.c b/remote.c
index fe62068463..017cd9d13e 100644
--- a/remote.c
+++ b/remote.c
@@ -152,6 +152,7 @@ static struct remote *make_remote(struct remote_state *remote_state,
 	ret->name = xstrndup(name, len);
 	refspec_init_push(&ret->push, the_hash_algo);
 	refspec_init_fetch(&ret->fetch, the_hash_algo);
+	refspec_init_fetch(&ret->refmap, the_hash_algo);
 	string_list_init_dup(&ret->server_options);
 	string_list_init_dup(&ret->negotiation_restrict);
 	string_list_init_dup(&ret->negotiation_include);
@@ -176,6 +177,7 @@ static void remote_clear(struct remote *remote)
 
 	refspec_clear(&remote->push);
 	refspec_clear(&remote->fetch);
+	refspec_clear(&remote->refmap);
 
 	free((char *)remote->receivepack);
 	free((char *)remote->uploadpack);
@@ -539,6 +541,12 @@ static int handle_config(const char *key, const char *value,
 			return -1;
 		refspec_append(&remote->fetch, v);
 		free(v);
+	} else if (!strcmp(subkey, "refmap")) {
+		char *v;
+		if (git_config_string(&v, key, value))
+			return -1;
+		refspec_append(&remote->refmap, v);
+		free(v);
 	} else if (!strcmp(subkey, "receivepack")) {
 		char *v;
 		if (git_config_string(&v, key, value))
@@ -988,7 +996,9 @@ void ref_push_report_free(struct ref_push_report *report)
 
 int remote_find_tracking(struct remote *remote, struct refspec_item *refspec)
 {
-	return refspec_find_match(&remote->fetch, refspec);
+	if (remote->fetch.nr)
+		return refspec_find_match(&remote->fetch, refspec);
+	return refspec_find_match(&remote->refmap, refspec);
 }
 
 static struct ref *alloc_ref_with_prefix(const char *prefix, size_t prefixlen,
diff --git a/remote.h b/remote.h
index cca02033b9..ac485a584d 100644
--- a/remote.h
+++ b/remote.h
@@ -90,6 +90,12 @@ struct remote {
 
 	struct refspec fetch;
 
+	/*
+	 * How to map refs fetched without an explicit destination into our
+	 * own namespace, the same as the --refmap command line option.
+	 */
+	struct refspec refmap;
+
 	/*
 	 * The setting for whether to fetch tags (as a separate rule from the
 	 * configured refspecs);
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index a8d38d9176..bd853d0a84 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -927,6 +927,23 @@ test_expect_success 'explicit --refmap option overrides remote.*.fetch' '
 	)
 '
 
+test_expect_success 'remote.*.refmap acts like --refmap on the command line' '
+	test_when_finished "git -C three config --unset remote.origin.refmap" &&
+	git branch -f side &&
+	git -C three config remote.origin.refmap \
+		"refs/heads/*:refs/remotes/other/*" &&
+	(
+		cd three &&
+		git update-ref refs/remotes/origin/main base-origin-main &&
+		o=$(git rev-parse --verify refs/remotes/origin/main) &&
+		git fetch origin main &&
+		n=$(git rev-parse --verify refs/remotes/origin/main) &&
+		test "$o" = "$n" &&
+		test_must_fail git rev-parse --verify refs/remotes/origin/side &&
+		git rev-parse --verify refs/remotes/other/main
+	)
+'
+
 test_expect_success 'explicitly empty --refmap option disables remote.*.fetch' '
 	git branch -f side &&
 	(

Documentation/config/remote.adoc, Documentation/fetch-options.adoc, builtin/fetch.c, remote.c, remote.h, t/meson.build, t/t5585-fetch-refmap.sh

diff --git a/Documentation/config/remote.adoc b/Documentation/config/remote.adoc
index 00f9ed8d3d..5b68af3af1 100644
--- a/Documentation/config/remote.adoc
+++ b/Documentation/config/remote.adoc
@@ -35,9 +35,10 @@ remote.<name>.fetch::
 
 remote.<name>.refmap::
 	The default value of the `--refmap` option for linkgit:git-fetch[1].
-	Only takes effect when the fetch names what to fetch explicitly,
-	either on the command line or via `remote.<name>.fetch`. See the
-	`--refmap` entry in linkgit:git-fetch[1].
+	If `remote.<name>.fetch` is not set either, a refspec-less fetch
+	infers what to fetch from local branches built on this remote,
+	instead of fetching every branch it has. See the `--refmap` entry
+	in linkgit:git-fetch[1].
 
 remote.<name>.push::
 	The default set of "refspec" for linkgit:git-push[1]. See
diff --git a/Documentation/fetch-options.adoc b/Documentation/fetch-options.adoc
index 538914bc6e..c973a07caf 100644
--- a/Documentation/fetch-options.adoc
+++ b/Documentation/fetch-options.adoc
@@ -245,8 +245,12 @@ endif::git-pull[]
 	command-line arguments. See section on "Configured Remote-tracking
 	Branches" for details.
 +
-`remote.<name>.refmap` provides the default value for this option, the
-same way `remote.<name>.fetch` provides the default refspecs to fetch.
+When a refmap is active (from `--refmap` or `remote.<name>.refmap`) but
+there is nothing to fetch, neither on the command line nor from
+`remote.<name>.fetch`, Git infers what to fetch from the local branches
+whose `@{upstream}` is on that remote, plus the remote's default branch,
+which is always included so that it is available even before anything
+is set up to track it.
 
 `-t`::
 `--tags`::
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 7651b41139..c8ce89cf30 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -503,7 +503,8 @@ static void filter_prefetch_refspec(struct refspec *rs)
 static struct ref *get_ref_map(struct remote *remote,
 			       const struct ref *remote_refs,
 			       struct refspec *rs,
-			       int tags, int *autotags)
+			       int tags, int *autotags,
+			       char **bootstrap_head_branch)
 {
 	int i;
 	struct ref *rm;
@@ -511,6 +512,8 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct ref **tail = &ref_map;
 	struct refspec *effective_refmap =
 		refmap.nr ? &refmap : remote ? &remote->refmap : NULL;
+	struct refspec inferred_rs;
+	int inferred_branches = 0;
 
 	/* opportunistically-updated references: */
 	struct ref *orefs = NULL, **oref_tail = &orefs;
@@ -518,15 +521,71 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct hashmap existing_refs;
 	int existing_refs_populated = 0;
 
+	refspec_init_fetch(&inferred_rs, the_hash_algo);
+
 	filter_prefetch_refspec(rs);
 	if (remote)
 		filter_prefetch_refspec(&remote->fetch);
 
+	if (!rs->nr && remote && !remote->fetch.nr &&
+	    effective_refmap && effective_refmap->nr) {
+		struct string_list tracked = STRING_LIST_INIT_DUP;
+		struct string_list_item *item;
+		struct ref *head;
+		char *default_branch = NULL;
+		char *default_branch_dst = NULL;
+
+		branches_tracking_remote(remote, &tracked);
+		for_each_string_list_item(item, &tracked)
+			refspec_append(&inferred_rs, item->string);
+
+		/* Always fetch the default branch too, as "HEAD". */
+		head = get_remote_ref(remote_refs, "HEAD");
+		if (head && head->symref && *head->symref)
+			default_branch = xstrdup(head->symref);
+		free_one_ref(head);
+
+		for (i = 0; default_branch && !default_branch_dst &&
+			    !string_list_has_string(&tracked, default_branch) &&
+			    i < effective_refmap->nr; i++) {
+			struct refspec_item *map = &effective_refmap->items[i];
+
+			if (map->pattern)
+				match_refname_with_pattern(map->src, default_branch,
+							    map->dst, &default_branch_dst);
+			else if (!strcmp(map->src, default_branch))
+				default_branch_dst = xstrdup(map->dst);
+		}
+
+		if (default_branch_dst) {
+			struct refspec_item head_item = { .force = 1 };
+
+			head_item.src = xstrdup("HEAD");
+			head_item.dst = default_branch_dst;
+			get_fetch_map(remote_refs, &head_item, &tail, 1);
+			free(head_item.src);
+		}
+
+		if (default_branch && bootstrap_head_branch) {
+			const char *branch_name = default_branch;
+			skip_prefix(branch_name, "refs/heads/", &branch_name);
+			*bootstrap_head_branch = xstrdup(branch_name);
+		}
+
+		free(default_branch);
+		free(default_branch_dst);
+		string_list_clear(&tracked, 0);
+
+		rs = &inferred_rs;
+		inferred_branches = 1;
+	}
+
 	if (rs->nr) {
 		struct refspec *fetch_refspec;
 
 		for (i = 0; i < rs->nr; i++) {
-			get_fetch_map(remote_refs, &rs->items[i], &tail, 0);
+			get_fetch_map(remote_refs, &rs->items[i], &tail,
+				      inferred_branches);
 			if (rs->items[i].dst && rs->items[i].dst[0])
 				*autotags = 1;
 		}
@@ -561,6 +620,8 @@ static struct ref *get_ref_map(struct remote *remote,
 
 		for (i = 0; i < fetch_refspec->nr; i++)
 			get_fetch_map(ref_map, &fetch_refspec->items[i], &oref_tail, 1);
+	} else if (inferred_branches) {
+		/* Already fully handled above. */
 	} else if (effective_refmap && effective_refmap->nr) {
 		die("--refmap option is only meaningful with command-line refspec(s)");
 	} else {
@@ -656,6 +717,7 @@ static struct ref *get_ref_map(struct remote *remote,
 	if (existing_refs_populated)
 		hashmap_clear_and_free(&existing_refs, struct refname_hash_entry, ent);
 
+	refspec_clear(&inferred_rs);
 	return ref_map;
 }
 
@@ -1753,14 +1815,14 @@ static void warn_set_head(const char *remote, const char *head_name,
 }
 
 static int set_head(const struct ref *remote_refs, struct remote *remote,
-			int follow_remote_head)
+			int follow_remote_head, const char *known_head_branch)
 {
 	int result = 0, create_only, baremirror, was_detached;
 	struct strbuf b_head = STRBUF_INIT, b_remote_head = STRBUF_INIT,
 		      b_local_head = STRBUF_INIT;
 	const char *no_warn_branch = remote->no_warn_branch;
 	char *head_name = NULL;
-	struct ref *ref, *matches;
+	struct ref *ref, *matches = NULL;
 	struct ref *fetch_map = NULL, **fetch_map_tail = &fetch_map;
 	struct refspec_item refspec = {
 		.force = 0,
@@ -1771,19 +1833,23 @@ static int set_head(const struct ref *remote_refs, struct remote *remote,
 	struct string_list heads = STRING_LIST_INIT_DUP;
 	struct ref_store *refs = get_main_ref_store(the_repository);
 
-	get_fetch_map(remote_refs, &refspec, &fetch_map_tail, 0);
-	matches = guess_remote_head(find_ref_by_name(remote_refs, "HEAD"),
-				    fetch_map, REMOTE_GUESS_HEAD_ALL);
-	for (ref = matches; ref; ref = ref->next) {
-		string_list_append(&heads, strip_refshead(ref->name));
-	}
+	if (known_head_branch) {
+		head_name = xstrdup(known_head_branch);
+	} else {
+		get_fetch_map(remote_refs, &refspec, &fetch_map_tail, 0);
+		matches = guess_remote_head(find_ref_by_name(remote_refs, "HEAD"),
+					    fetch_map, REMOTE_GUESS_HEAD_ALL);
+		for (ref = matches; ref; ref = ref->next) {
+			string_list_append(&heads, strip_refshead(ref->name));
+		}
 
-	if (!heads.nr)
-		result = 1;
-	else if (heads.nr > 1)
-		result = 1;
-	else
-		head_name = xstrdup(heads.items[0].string);
+		if (!heads.nr)
+			result = 1;
+		else if (heads.nr > 1)
+			result = 1;
+		else
+			head_name = xstrdup(heads.items[0].string);
+	}
 
 	if (!head_name)
 		goto cleanup;
@@ -1925,6 +1991,7 @@ static int do_fetch(struct transport *transport,
 	struct strmap rejected_refs = STRMAP_INIT;
 	int summary_width = 0;
 	int follow_remote_head;
+	char *bootstrap_head_branch = NULL;
 
 	if (tags == TAGS_DEFAULT) {
 		if (transport->remote->fetch_tags == 2)
@@ -1960,15 +2027,31 @@ static int do_fetch(struct transport *transport,
 		refspec_ref_prefixes(rs, &transport_ls_refs_options.ref_prefixes);
 	} else {
 		struct branch *branch = branch_get(NULL);
-
-		if (transport->remote->fetch.nr) {
+		int tracks_this_remote = branch && branch_has_merge_config(branch) &&
+			!strcmp(branch->remote_name, transport->remote->name);
+		struct refspec *effective_refmap = refmap.nr ? &refmap :
+			&transport->remote->refmap;
+		int inferred_branches = !transport->remote->fetch.nr &&
+			effective_refmap->nr;
+
+		if (inferred_branches) {
+			struct string_list tracked = STRING_LIST_INIT_DUP;
+			struct string_list_item *item;
+
+			branches_tracking_remote(transport->remote, &tracked);
+			for_each_string_list_item(item, &tracked)
+				strvec_push(&transport_ls_refs_options.ref_prefixes,
+					    item->string);
+			string_list_clear(&tracked, 0);
+			strvec_push(&transport_ls_refs_options.ref_prefixes, "HEAD");
+		} else if (transport->remote->fetch.nr) {
 			refspec_ref_prefixes(&transport->remote->fetch,
 					     &transport_ls_refs_options.ref_prefixes);
-			if (follow_remote_head != FOLLOW_REMOTE_NEVER)
-				do_set_head = 1;
 		}
-		if (branch && branch_has_merge_config(branch) &&
-		    !strcmp(branch->remote_name, transport->remote->name)) {
+		if ((transport->remote->fetch.nr || inferred_branches) &&
+		    follow_remote_head != FOLLOW_REMOTE_NEVER)
+			do_set_head = 1;
+		if (tracks_this_remote) {
 			int i;
 			for (i = 0; i < branch->merge_nr; i++) {
 				strvec_push(&transport_ls_refs_options.ref_prefixes,
@@ -2008,7 +2091,8 @@ static int do_fetch(struct transport *transport,
 	transport_ls_refs_options_release(&transport_ls_refs_options);
 
 	ref_map = get_ref_map(transport->remote, remote_refs, rs,
-			      tags, &autotags);
+			      tags, &autotags, &bootstrap_head_branch);
+
 	if (!update_head_ok)
 		check_not_current_branch(ref_map);
 
@@ -2171,10 +2255,12 @@ static int do_fetch(struct transport *transport,
 		 * Way too many cases where this can go wrong so let's just
 		 * ignore errors and fail silently for now.
 		 */
-		set_head(remote_refs, transport->remote, follow_remote_head);
+		set_head(remote_refs, transport->remote, follow_remote_head,
+			 bootstrap_head_branch);
 	}
 
 cleanup:
+	free(bootstrap_head_branch);
 	/*
 	 * When using batched updates, we want to commit the non-rejected
 	 * updates and also handle the rejections.
diff --git a/remote.c b/remote.c
index 017cd9d13e..a5deb9b929 100644
--- a/remote.c
+++ b/remote.c
@@ -1884,6 +1884,35 @@ int branch_merge_matches(struct branch *branch,
 	return refname_match(branch->merge[i]->src, refname);
 }
 
+struct branches_tracking_remote_cb_data {
+	struct remote *remote;
+	struct string_list *tracked;
+};
+
+static int add_if_tracking_remote(const struct reference *ref, void *cb_data)
+{
+	struct branches_tracking_remote_cb_data *data = cb_data;
+	struct branch *branch;
+
+	branch = branch_get(ref->name);
+	if (!branch_has_merge_config(branch) ||
+	    strcmp(branch->remote_name, data->remote->name))
+		return 0;
+
+	for (int i = 0; i < branch->merge_nr; i++)
+		string_list_insert(data->tracked, branch->merge[i]->src);
+
+	return 0;
+}
+
+void branches_tracking_remote(struct remote *remote, struct string_list *tracked)
+{
+	struct branches_tracking_remote_cb_data data = { remote, tracked };
+
+	refs_for_each_branch_ref(get_main_ref_store(the_repository),
+				  add_if_tracking_remote, &data);
+}
+
 __attribute__((format (printf,2,3)))
 static char *error_buf(struct strbuf *err, const char *fmt, ...)
 {
diff --git a/remote.h b/remote.h
index ac485a584d..da6c3ef53a 100644
--- a/remote.h
+++ b/remote.h
@@ -359,6 +359,9 @@ int branch_has_merge_config(struct branch *branch);
 
 int branch_merge_matches(struct branch *, int n, const char *);
 
+/* fills tracked with the refname of every local branch's upstream on remote */
+void branches_tracking_remote(struct remote *remote, struct string_list *tracked);
+
 /* list of the remote in a group as configured */
 struct remote_group_data {
 	const char *name;
diff --git a/t/meson.build b/t/meson.build
index 3ca7b27104..ab83d5409c 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -728,6 +728,7 @@ integration_tests = [
   't5582-fetch-negative-refspec.sh',
   't5583-push-branches.sh',
   't5584-http-429-retry.sh',
+  't5585-fetch-refmap.sh',
   't5600-clone-fail-cleanup.sh',
   't5601-clone.sh',
   't5602-clone-remote-exec.sh',
diff --git a/t/t5585-fetch-refmap.sh b/t/t5585-fetch-refmap.sh
new file mode 100755
index 0000000000..4b1f51f6cd
--- /dev/null
+++ b/t/t5585-fetch-refmap.sh
@@ -0,0 +1,124 @@
+#!/bin/sh
+
+test_description='"git fetch" with a remote.<name>.refmap but no remote.<name>.fetch
+
+When a remote has a refmap configured but no fetch refspec, a
+refspec-less fetch infers what to fetch from the local branches whose
+@{upstream} is on that remote, plus the default branch of that remote,
+which is always included so that it is available even before anything
+is set up to track it.
+'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit main-1 &&
+	test_commit main-2 &&
+	git checkout -b side main-1 &&
+	test_commit side-1 &&
+	git checkout -b next main-1 &&
+	test_commit next-1 &&
+	git checkout main
+'
+
+test_expect_success 'clone shallow and single-branch, then add a second remote' '
+	git clone --no-local --depth=1 --branch main --single-branch . client &&
+	(
+		cd client &&
+		git remote add upstream .. &&
+		test_might_fail git config unset remote.upstream.fetch &&
+		git config remote.upstream.refmap \
+			"+refs/heads/*:refs/remotes/upstream/*"
+	)
+'
+
+test_expect_success 'fetching the new remote does not need every branch it has' '
+	(
+		cd client &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'set-upstream-to now resolves right after that first fetch' '
+	(
+		cd client &&
+		git branch --set-upstream-to=upstream &&
+		test_cmp_config upstream branch.main.remote &&
+		test_cmp_config refs/heads/main branch.main.merge
+	)
+'
+
+test_expect_success 'a branch checked out from a one-time fetch is kept updated by later plain fetches' '
+	(
+		cd client &&
+		git fetch upstream side:refs/remotes/upstream/side &&
+		git branch side-topic upstream/side
+	) &&
+	git checkout side &&
+	test_commit side-2 &&
+	git checkout main &&
+	(
+		cd client &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual &&
+		git rev-parse refs/remotes/upstream/side >actual-oid &&
+		git -C .. rev-parse side >expect-oid &&
+		test_cmp expect-oid actual-oid
+	)
+'
+
+test_expect_success 'a second branch tracking the same upstream branch does not fetch it twice' '
+	(
+		cd client &&
+		git branch side-topic-2 upstream/side &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'a branch tracking a different remote is not fetched from upstream' '
+	(
+		cd client &&
+		git remote add other .. &&
+		git fetch other next:refs/remotes/other/next &&
+		git branch next-topic other/next &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'git remote show does not choke on a refmap-only remote' '
+	(
+		cd client &&
+		git remote show upstream
+	)
+'
+
+test_done

Documentation/git-remote.adoc, builtin/remote.c, t/t5505-remote.sh

diff --git a/Documentation/git-remote.adoc b/Documentation/git-remote.adoc
index eaae30aa88..74fbce6e0e 100644
--- a/Documentation/git-remote.adoc
+++ b/Documentation/git-remote.adoc
@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 [synopsis]
 git remote [-v | --verbose]
-git remote add [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=(fetch|push)] <name> <URL>
+git remote add [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=(fetch|push)] [--[no-]limited-fetch] <name> <URL>
 git remote rename [--[no-]progress] <old> <new>
 git remote remove <name>
 git remote set-head <name> (-a | --auto | -d | --delete | <branch>)
@@ -70,6 +70,12 @@ the `refs/remotes/<name>/` namespace, a refspec to track only _<branch>_
 is created.  You can give more than one `-t <branch>` to track
 multiple branches without grabbing all branches.
 +
+With `--limited-fetch` option, instead of a `remote.<name>.fetch` refspec
+that tracks all branches, `remote.<name>.refmap` is set up so that a
+refspec-less `git fetch <name>` only fetches branches our local branches
+are built on, plus the remote's default branch. See the `--refmap` entry
+in linkgit:git-fetch[1] for details.
++
 With `-m <master>` option, a symbolic-ref `refs/remotes/<name>/HEAD` is set
 up to point at remote's _<master>_ branch. See also the set-head command.
 +
diff --git a/builtin/remote.c b/builtin/remote.c
index de989ea3ba..f036dd5d6f 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -179,6 +179,7 @@ static int add(int argc, const char **argv, const char *prefix,
 {
 	int fetch = 0, fetch_tags = TAGS_DEFAULT;
 	unsigned mirror = MIRROR_NONE;
+	int limited_fetch = -1; /* unspecified */
 	struct string_list track = STRING_LIST_INIT_NODUP;
 	const char *master = NULL;
 	struct remote *remote;
@@ -198,6 +199,8 @@ static int add(int argc, const char **argv, const char *prefix,
 		OPT_CALLBACK_F(0, "mirror", &mirror, "(push|fetch)",
 			N_("set up remote as a mirror to push to or fetch from"),
 			PARSE_OPT_OPTARG | PARSE_OPT_COMP_ARG, parse_mirror_opt),
+		OPT_BOOL(0, "limited-fetch", &limited_fetch,
+			N_("fetch only the branches we build on, instead of every branch")),
 		OPT_END()
 	};
 
@@ -211,6 +214,10 @@ static int add(int argc, const char **argv, const char *prefix,
 		die(_("specifying a master branch makes no sense with --mirror"));
 	if (mirror && !(mirror & MIRROR_FETCH) && track.nr)
 		die(_("specifying branches to track makes sense only with fetch mirrors"));
+	if (limited_fetch == 1 && track.nr)
+		die(_("--limited-fetch does not make sense with -t/--track"));
+	if (limited_fetch == 1 && mirror)
+		die(_("--limited-fetch does not make sense with --mirror"));
 
 	name = argv[0];
 	url = argv[1];
@@ -230,13 +237,22 @@ static int add(int argc, const char **argv, const char *prefix,
 	repo_config_set(the_repository, buf.buf, url);
 
 	if (!mirror || mirror & MIRROR_FETCH) {
+		int use_limited_fetch = mirror == MIRROR_NONE && track.nr == 0 &&
+			limited_fetch == 1;
+
 		strbuf_reset(&buf);
-		strbuf_addf(&buf, "remote.%s.fetch", name);
-		if (track.nr == 0)
-			string_list_append(&track, "*");
-		for (size_t i = 0; i < track.nr; i++) {
-			add_branch(buf.buf, track.items[i].string,
-				   name, mirror, &buf2);
+		if (use_limited_fetch) {
+			strbuf_addf(&buf, "remote.%s.refmap", name);
+			strbuf_reset(&buf2);
+			strbuf_addf(&buf2, "+refs/heads/*:refs/remotes/%s/*", name);
+			repo_config_set(the_repository, buf.buf, buf2.buf);
+		} else {
+			strbuf_addf(&buf, "remote.%s.fetch", name);
+			if (track.nr == 0)
+				string_list_append(&track, "*");
+			for (size_t i = 0; i < track.nr; i++)
+				add_branch(buf.buf, track.items[i].string,
+					   name, mirror, &buf2);
 		}
 	}
 
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 5fbfcb0848..0168d5abfe 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -137,6 +137,22 @@ test_expect_success 'filters are listed by git remote -v only' '
 	test_grep ! "\[blob:none\]" out
 '
 
+test_expect_success '--limited-fetch works in a full repository too' '
+	test_when_finished "rm -rf full-add" &&
+	git clone --no-local one full-add &&
+	(
+		cd full-add &&
+		git remote add --limited-fetch upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.refmap &&
+		test_must_fail git config get remote.upstream.fetch
+	)
+'
+
+test_expect_success '--limited-fetch conflicts with -t' '
+	test_must_fail git remote add --limited-fetch -t main upstream ../two
+'
+
 test_expect_success 'check remote-tracking' '
 	(
 		cd test &&

Documentation/git-remote.adoc, builtin/remote.c, t/t5505-remote.sh

diff --git a/Documentation/git-remote.adoc b/Documentation/git-remote.adoc
index 74fbce6e0e..82b21eafa7 100644
--- a/Documentation/git-remote.adoc
+++ b/Documentation/git-remote.adoc
@@ -52,6 +52,11 @@ Add a remote named _<name>_ for the repository at
 _<URL>_.  The command `git fetch <name>` can then be used to create and
 update remote-tracking branches `<name>/<branch>`.
 +
+If the repository is already a shallow repository (see linkgit:git-clone[1]
+`--depth`) and neither `-t`, `--mirror` nor `--no-limited-fetch` is given,
+`--limited-fetch` is turned on by default, so that `git fetch <name>` does
+not need to negotiate history for every branch the remote has.
++
 With `-f` option, `git fetch <name>` is run immediately after
 the remote information is set up.
 +
@@ -74,7 +79,8 @@ With `--limited-fetch` option, instead of a `remote.<name>.fetch` refspec
 that tracks all branches, `remote.<name>.refmap` is set up so that a
 refspec-less `git fetch <name>` only fetches branches our local branches
 are built on, plus the remote's default branch. See the `--refmap` entry
-in linkgit:git-fetch[1] for details.
+in linkgit:git-fetch[1] for details. `--no-limited-fetch` explicitly
+disables this, overriding the shallow-repository default described above.
 +
 With `-m <master>` option, a symbolic-ref `refs/remotes/<name>/HEAD` is set
 up to point at remote's _<master>_ branch. See also the set-head command.
diff --git a/builtin/remote.c b/builtin/remote.c
index f036dd5d6f..0cf1126976 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -16,6 +16,7 @@
 #include "rebase.h"
 #include "refs.h"
 #include "refspec.h"
+#include "shallow.h"
 #include "odb.h"
 #include "strvec.h"
 #include "commit-reach.h"
@@ -238,7 +239,9 @@ static int add(int argc, const char **argv, const char *prefix,
 
 	if (!mirror || mirror & MIRROR_FETCH) {
 		int use_limited_fetch = mirror == MIRROR_NONE && track.nr == 0 &&
-			limited_fetch == 1;
+			(limited_fetch == 1 ||
+			 (limited_fetch == -1 &&
+			  is_repository_shallow(the_repository)));
 
 		strbuf_reset(&buf);
 		if (use_limited_fetch) {
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 0168d5abfe..9cb88d8806 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -137,6 +137,65 @@ test_expect_success 'filters are listed by git remote -v only' '
 	test_grep ! "\[blob:none\]" out
 '
 
+test_expect_success 'add remote -t keeps an explicit refspec in a shallow repository' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add -t main upstream ../two &&
+		test_cmp_config "+refs/heads/main:refs/remotes/upstream/main" \
+			remote.upstream.fetch
+	)
+'
+
+test_expect_success 'add remote keeps the wildcard refspec in a full repository' '
+	test_when_finished "rm -rf full-add" &&
+	git clone --no-local one full-add &&
+	(
+		cd full-add &&
+		git remote add upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.fetch
+	)
+'
+
+test_expect_success 'a remote added in a shallow repository defaults to --limited-fetch' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.refmap &&
+		test_must_fail git config get remote.upstream.fetch &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		EOF
+		test_cmp expect actual &&
+		git branch --set-upstream-to=upstream &&
+		test_cmp_config upstream branch.main.remote &&
+		test_cmp_config refs/heads/main branch.main.merge
+	)
+'
+
+test_expect_success '--no-limited-fetch overrides the shallow-repository default' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add --no-limited-fetch upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.fetch &&
+		test_must_fail git config get remote.upstream.refmap
+	)
+'
+
 test_expect_success '--limited-fetch works in a full repository too' '
 	test_when_finished "rm -rf full-add" &&
 	git clone --no-local one full-add &&

Documentation/config/remote.adoc, Documentation/fetch-options.adoc, builtin/fetch.c, remote.c, remote.h, t/t5510-fetch.sh

diff --git a/Documentation/config/remote.adoc b/Documentation/config/remote.adoc
index 3a20d0f752..103eada406 100644
--- a/Documentation/config/remote.adoc
+++ b/Documentation/config/remote.adoc
@@ -33,6 +33,11 @@ remote.<name>.fetch::
 	The default set of "refspec" for linkgit:git-fetch[1]. See
 	linkgit:git-fetch[1].
 
+remote.<name>.refmap::
+	The default value of the `--refmap` option for linkgit:git-fetch[1].
+	Used to map remote refs being fetched to remote-tracking refs to
+	store. See the `--refmap` entry in linkgit:git-fetch[1].
+
 remote.<name>.push::
 	The default set of "refspec" for linkgit:git-push[1]. See
 	linkgit:git-push[1].
diff --git a/Documentation/fetch-options.adoc b/Documentation/fetch-options.adoc
index 035f780e58..538914bc6e 100644
--- a/Documentation/fetch-options.adoc
+++ b/Documentation/fetch-options.adoc
@@ -244,6 +244,9 @@ endif::git-pull[]
 	refspecs and rely entirely on the refspecs supplied as
 	command-line arguments. See section on "Configured Remote-tracking
 	Branches" for details.
++
+`remote.<name>.refmap` provides the default value for this option, the
+same way `remote.<name>.fetch` provides the default refspecs to fetch.
 
 `-t`::
 `--tags`::
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 533fdfe7d8..7651b41139 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -509,6 +509,8 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct ref *rm;
 	struct ref *ref_map = NULL;
 	struct ref **tail = &ref_map;
+	struct refspec *effective_refmap =
+		refmap.nr ? &refmap : remote ? &remote->refmap : NULL;
 
 	/* opportunistically-updated references: */
 	struct ref *orefs = NULL, **oref_tail = &orefs;
@@ -552,14 +554,14 @@ static struct ref *get_ref_map(struct remote *remote,
 		 * by ref_remove_duplicates() in favor of one of these
 		 * opportunistic entries with FETCH_HEAD_IGNORE.
 		 */
-		if (refmap.nr)
-			fetch_refspec = &refmap;
+		if (effective_refmap && effective_refmap->nr)
+			fetch_refspec = effective_refmap;
 		else
 			fetch_refspec = &remote->fetch;
 
 		for (i = 0; i < fetch_refspec->nr; i++)
 			get_fetch_map(ref_map, &fetch_refspec->items[i], &oref_tail, 1);
-	} else if (refmap.nr) {
+	} else if (effective_refmap && effective_refmap->nr) {
 		die("--refmap option is only meaningful with command-line refspec(s)");
 	} else {
 		/* Use the defaults */
diff --git a/remote.c b/remote.c
index fe62068463..017cd9d13e 100644
--- a/remote.c
+++ b/remote.c
@@ -152,6 +152,7 @@ static struct remote *make_remote(struct remote_state *remote_state,
 	ret->name = xstrndup(name, len);
 	refspec_init_push(&ret->push, the_hash_algo);
 	refspec_init_fetch(&ret->fetch, the_hash_algo);
+	refspec_init_fetch(&ret->refmap, the_hash_algo);
 	string_list_init_dup(&ret->server_options);
 	string_list_init_dup(&ret->negotiation_restrict);
 	string_list_init_dup(&ret->negotiation_include);
@@ -176,6 +177,7 @@ static void remote_clear(struct remote *remote)
 
 	refspec_clear(&remote->push);
 	refspec_clear(&remote->fetch);
+	refspec_clear(&remote->refmap);
 
 	free((char *)remote->receivepack);
 	free((char *)remote->uploadpack);
@@ -539,6 +541,12 @@ static int handle_config(const char *key, const char *value,
 			return -1;
 		refspec_append(&remote->fetch, v);
 		free(v);
+	} else if (!strcmp(subkey, "refmap")) {
+		char *v;
+		if (git_config_string(&v, key, value))
+			return -1;
+		refspec_append(&remote->refmap, v);
+		free(v);
 	} else if (!strcmp(subkey, "receivepack")) {
 		char *v;
 		if (git_config_string(&v, key, value))
@@ -988,7 +996,9 @@ void ref_push_report_free(struct ref_push_report *report)
 
 int remote_find_tracking(struct remote *remote, struct refspec_item *refspec)
 {
-	return refspec_find_match(&remote->fetch, refspec);
+	if (remote->fetch.nr)
+		return refspec_find_match(&remote->fetch, refspec);
+	return refspec_find_match(&remote->refmap, refspec);
 }
 
 static struct ref *alloc_ref_with_prefix(const char *prefix, size_t prefixlen,
diff --git a/remote.h b/remote.h
index cca02033b9..ac485a584d 100644
--- a/remote.h
+++ b/remote.h
@@ -90,6 +90,12 @@ struct remote {
 
 	struct refspec fetch;
 
+	/*
+	 * How to map refs fetched without an explicit destination into our
+	 * own namespace, the same as the --refmap command line option.
+	 */
+	struct refspec refmap;
+
 	/*
 	 * The setting for whether to fetch tags (as a separate rule from the
 	 * configured refspecs);
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index a8d38d9176..bd853d0a84 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -927,6 +927,23 @@ test_expect_success 'explicit --refmap option overrides remote.*.fetch' '
 	)
 '
 
+test_expect_success 'remote.*.refmap acts like --refmap on the command line' '
+	test_when_finished "git -C three config --unset remote.origin.refmap" &&
+	git branch -f side &&
+	git -C three config remote.origin.refmap \
+		"refs/heads/*:refs/remotes/other/*" &&
+	(
+		cd three &&
+		git update-ref refs/remotes/origin/main base-origin-main &&
+		o=$(git rev-parse --verify refs/remotes/origin/main) &&
+		git fetch origin main &&
+		n=$(git rev-parse --verify refs/remotes/origin/main) &&
+		test "$o" = "$n" &&
+		test_must_fail git rev-parse --verify refs/remotes/origin/side &&
+		git rev-parse --verify refs/remotes/other/main
+	)
+'
+
 test_expect_success 'explicitly empty --refmap option disables remote.*.fetch' '
 	git branch -f side &&
 	(

Documentation/config/remote.adoc, Documentation/fetch-options.adoc, builtin/fetch.c, remote.c, remote.h, t/meson.build, t/t5585-fetch-refmap.sh

diff --git a/Documentation/config/remote.adoc b/Documentation/config/remote.adoc
index 103eada406..7c52e443a5 100644
--- a/Documentation/config/remote.adoc
+++ b/Documentation/config/remote.adoc
@@ -36,7 +36,10 @@ remote.<name>.fetch::
 remote.<name>.refmap::
 	The default value of the `--refmap` option for linkgit:git-fetch[1].
 	Used to map remote refs being fetched to remote-tracking refs to
-	store. See the `--refmap` entry in linkgit:git-fetch[1].
+	store. If `remote.<name>.fetch` is not set either, a refspec-less
+	fetch infers what to fetch from local branches built on this
+	remote, instead of fetching every branch it has. See the
+	`--refmap` entry in linkgit:git-fetch[1].
 
 remote.<name>.push::
 	The default set of "refspec" for linkgit:git-push[1]. See
diff --git a/Documentation/fetch-options.adoc b/Documentation/fetch-options.adoc
index 538914bc6e..315daf97d7 100644
--- a/Documentation/fetch-options.adoc
+++ b/Documentation/fetch-options.adoc
@@ -245,8 +245,10 @@ endif::git-pull[]
 	command-line arguments. See section on "Configured Remote-tracking
 	Branches" for details.
 +
-`remote.<name>.refmap` provides the default value for this option, the
-same way `remote.<name>.fetch` provides the default refspecs to fetch.
+When a refmap is active (from `--refmap` or `remote.<name>.refmap`) but
+there is nothing to fetch, neither on the command line nor from
+`remote.<name>.fetch`, Git infers what to fetch from the local branches
+whose `@{upstream}` is on that remote.
 
 `-t`::
 `--tags`::
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 7651b41139..7ef2776f17 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -511,6 +511,8 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct ref **tail = &ref_map;
 	struct refspec *effective_refmap =
 		refmap.nr ? &refmap : remote ? &remote->refmap : NULL;
+	struct refspec inferred_rs;
+	int inferred_branches = 0;
 
 	/* opportunistically-updated references: */
 	struct ref *orefs = NULL, **oref_tail = &orefs;
@@ -518,15 +520,32 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct hashmap existing_refs;
 	int existing_refs_populated = 0;
 
+	refspec_init_fetch(&inferred_rs, the_hash_algo);
+
 	filter_prefetch_refspec(rs);
 	if (remote)
 		filter_prefetch_refspec(&remote->fetch);
 
+	if (!rs->nr && remote && !remote->fetch.nr &&
+	    effective_refmap && effective_refmap->nr) {
+		struct string_list tracked = STRING_LIST_INIT_DUP;
+		struct string_list_item *item;
+
+		branches_tracking_remote(remote, &tracked);
+		for_each_string_list_item(item, &tracked)
+			refspec_append(&inferred_rs, item->string);
+		string_list_clear(&tracked, 0);
+
+		rs = &inferred_rs;
+		inferred_branches = 1;
+	}
+
 	if (rs->nr) {
 		struct refspec *fetch_refspec;
 
 		for (i = 0; i < rs->nr; i++) {
-			get_fetch_map(remote_refs, &rs->items[i], &tail, 0);
+			get_fetch_map(remote_refs, &rs->items[i], &tail,
+				      inferred_branches);
 			if (rs->items[i].dst && rs->items[i].dst[0])
 				*autotags = 1;
 		}
@@ -561,6 +580,8 @@ static struct ref *get_ref_map(struct remote *remote,
 
 		for (i = 0; i < fetch_refspec->nr; i++)
 			get_fetch_map(ref_map, &fetch_refspec->items[i], &oref_tail, 1);
+	} else if (inferred_branches) {
+		/* Already fully handled above. */
 	} else if (effective_refmap && effective_refmap->nr) {
 		die("--refmap option is only meaningful with command-line refspec(s)");
 	} else {
@@ -656,6 +677,7 @@ static struct ref *get_ref_map(struct remote *remote,
 	if (existing_refs_populated)
 		hashmap_clear_and_free(&existing_refs, struct refname_hash_entry, ent);
 
+	refspec_clear(&inferred_rs);
 	return ref_map;
 }
 
@@ -1960,15 +1982,30 @@ static int do_fetch(struct transport *transport,
 		refspec_ref_prefixes(rs, &transport_ls_refs_options.ref_prefixes);
 	} else {
 		struct branch *branch = branch_get(NULL);
-
-		if (transport->remote->fetch.nr) {
+		int tracks_this_remote = branch && branch_has_merge_config(branch) &&
+			!strcmp(branch->remote_name, transport->remote->name);
+		struct refspec *effective_refmap = refmap.nr ? &refmap :
+			&transport->remote->refmap;
+		int inferred_branches = !transport->remote->fetch.nr &&
+			effective_refmap->nr;
+
+		if (inferred_branches) {
+			struct string_list tracked = STRING_LIST_INIT_DUP;
+			struct string_list_item *item;
+
+			branches_tracking_remote(transport->remote, &tracked);
+			for_each_string_list_item(item, &tracked)
+				strvec_push(&transport_ls_refs_options.ref_prefixes,
+					    item->string);
+			string_list_clear(&tracked, 0);
+		} else if (transport->remote->fetch.nr) {
 			refspec_ref_prefixes(&transport->remote->fetch,
 					     &transport_ls_refs_options.ref_prefixes);
-			if (follow_remote_head != FOLLOW_REMOTE_NEVER)
-				do_set_head = 1;
 		}
-		if (branch && branch_has_merge_config(branch) &&
-		    !strcmp(branch->remote_name, transport->remote->name)) {
+		if ((transport->remote->fetch.nr || inferred_branches) &&
+		    follow_remote_head != FOLLOW_REMOTE_NEVER)
+			do_set_head = 1;
+		if (tracks_this_remote) {
 			int i;
 			for (i = 0; i < branch->merge_nr; i++) {
 				strvec_push(&transport_ls_refs_options.ref_prefixes,
@@ -2009,6 +2046,7 @@ static int do_fetch(struct transport *transport,
 
 	ref_map = get_ref_map(transport->remote, remote_refs, rs,
 			      tags, &autotags);
+
 	if (!update_head_ok)
 		check_not_current_branch(ref_map);
 
diff --git a/remote.c b/remote.c
index 017cd9d13e..a5deb9b929 100644
--- a/remote.c
+++ b/remote.c
@@ -1884,6 +1884,35 @@ int branch_merge_matches(struct branch *branch,
 	return refname_match(branch->merge[i]->src, refname);
 }
 
+struct branches_tracking_remote_cb_data {
+	struct remote *remote;
+	struct string_list *tracked;
+};
+
+static int add_if_tracking_remote(const struct reference *ref, void *cb_data)
+{
+	struct branches_tracking_remote_cb_data *data = cb_data;
+	struct branch *branch;
+
+	branch = branch_get(ref->name);
+	if (!branch_has_merge_config(branch) ||
+	    strcmp(branch->remote_name, data->remote->name))
+		return 0;
+
+	for (int i = 0; i < branch->merge_nr; i++)
+		string_list_insert(data->tracked, branch->merge[i]->src);
+
+	return 0;
+}
+
+void branches_tracking_remote(struct remote *remote, struct string_list *tracked)
+{
+	struct branches_tracking_remote_cb_data data = { remote, tracked };
+
+	refs_for_each_branch_ref(get_main_ref_store(the_repository),
+				  add_if_tracking_remote, &data);
+}
+
 __attribute__((format (printf,2,3)))
 static char *error_buf(struct strbuf *err, const char *fmt, ...)
 {
diff --git a/remote.h b/remote.h
index ac485a584d..da6c3ef53a 100644
--- a/remote.h
+++ b/remote.h
@@ -359,6 +359,9 @@ int branch_has_merge_config(struct branch *branch);
 
 int branch_merge_matches(struct branch *, int n, const char *);
 
+/* fills tracked with the refname of every local branch's upstream on remote */
+void branches_tracking_remote(struct remote *remote, struct string_list *tracked);
+
 /* list of the remote in a group as configured */
 struct remote_group_data {
 	const char *name;
diff --git a/t/meson.build b/t/meson.build
index 3ca7b27104..ab83d5409c 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -728,6 +728,7 @@ integration_tests = [
   't5582-fetch-negative-refspec.sh',
   't5583-push-branches.sh',
   't5584-http-429-retry.sh',
+  't5585-fetch-refmap.sh',
   't5600-clone-fail-cleanup.sh',
   't5601-clone.sh',
   't5602-clone-remote-exec.sh',
diff --git a/t/t5585-fetch-refmap.sh b/t/t5585-fetch-refmap.sh
new file mode 100755
index 0000000000..b81fc48cbe
--- /dev/null
+++ b/t/t5585-fetch-refmap.sh
@@ -0,0 +1,119 @@
+#!/bin/sh
+
+test_description='"git fetch" with a remote.<name>.refmap but no remote.<name>.fetch
+
+When a remote has a refmap configured but no fetch refspec, a
+refspec-less fetch infers what to fetch from the local branches whose
+@{upstream} is on that remote.
+'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit main-1 &&
+	test_commit main-2 &&
+	git checkout -b side main-1 &&
+	test_commit side-1 &&
+	git checkout -b next main-1 &&
+	test_commit next-1 &&
+	git checkout main
+'
+
+test_expect_success 'clone shallow and single-branch, then add a second remote' '
+	git clone --no-local --depth=1 --branch main --single-branch . client &&
+	(
+		cd client &&
+		git remote add upstream .. &&
+		test_might_fail git config unset remote.upstream.fetch &&
+		git config remote.upstream.refmap \
+			"+refs/heads/*:refs/remotes/upstream/*"
+	)
+'
+
+test_expect_success 'a bare fetch needs nothing until a branch is tracked' '
+	(
+		cd client &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		test_must_be_empty actual
+	)
+'
+
+test_expect_success 'an explicit one-time fetch lets a branch be tracked' '
+	(
+		cd client &&
+		git fetch upstream main &&
+		git branch --set-upstream-to=upstream/main &&
+		test_cmp_config upstream branch.main.remote &&
+		test_cmp_config refs/heads/main branch.main.merge
+	)
+'
+
+test_expect_success 'a branch checked out from a one-time fetch is kept updated by later plain fetches' '
+	(
+		cd client &&
+		git fetch upstream side:refs/remotes/upstream/side &&
+		git branch side-topic upstream/side
+	) &&
+	git checkout side &&
+	test_commit side-2 &&
+	git checkout main &&
+	(
+		cd client &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual &&
+		git rev-parse refs/remotes/upstream/side >actual-oid &&
+		git -C .. rev-parse side >expect-oid &&
+		test_cmp expect-oid actual-oid
+	)
+'
+
+test_expect_success 'a second branch tracking the same upstream branch does not fetch it twice' '
+	(
+		cd client &&
+		git branch side-topic-2 upstream/side &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'a branch tracking a different remote is not fetched from upstream' '
+	(
+		cd client &&
+		git remote add other .. &&
+		git fetch other next:refs/remotes/other/next &&
+		git branch next-topic other/next &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'git remote show does not choke on a refmap-only remote' '
+	(
+		cd client &&
+		git remote show upstream
+	)
+'
+
+test_done

Documentation/git-remote.adoc, builtin/remote.c, t/t5505-remote.sh

diff --git a/Documentation/git-remote.adoc b/Documentation/git-remote.adoc
index eaae30aa88..4255f8b3e6 100644
--- a/Documentation/git-remote.adoc
+++ b/Documentation/git-remote.adoc
@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 [synopsis]
 git remote [-v | --verbose]
-git remote add [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=(fetch|push)] <name> <URL>
+git remote add [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=(fetch|push)] [--[no-]limited-fetch] <name> <URL>
 git remote rename [--[no-]progress] <old> <new>
 git remote remove <name>
 git remote set-head <name> (-a | --auto | -d | --delete | <branch>)
@@ -70,6 +70,12 @@ the `refs/remotes/<name>/` namespace, a refspec to track only _<branch>_
 is created.  You can give more than one `-t <branch>` to track
 multiple branches without grabbing all branches.
 +
+With `--limited-fetch` option, instead of a `remote.<name>.fetch` refspec
+that tracks all branches, `remote.<name>.refmap` is set up so that a
+refspec-less `git fetch <name>` only fetches branches our local branches
+are built on. See the `--refmap` entry in linkgit:git-fetch[1] for
+details.
++
 With `-m <master>` option, a symbolic-ref `refs/remotes/<name>/HEAD` is set
 up to point at remote's _<master>_ branch. See also the set-head command.
 +
diff --git a/builtin/remote.c b/builtin/remote.c
index de989ea3ba..f036dd5d6f 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -179,6 +179,7 @@ static int add(int argc, const char **argv, const char *prefix,
 {
 	int fetch = 0, fetch_tags = TAGS_DEFAULT;
 	unsigned mirror = MIRROR_NONE;
+	int limited_fetch = -1; /* unspecified */
 	struct string_list track = STRING_LIST_INIT_NODUP;
 	const char *master = NULL;
 	struct remote *remote;
@@ -198,6 +199,8 @@ static int add(int argc, const char **argv, const char *prefix,
 		OPT_CALLBACK_F(0, "mirror", &mirror, "(push|fetch)",
 			N_("set up remote as a mirror to push to or fetch from"),
 			PARSE_OPT_OPTARG | PARSE_OPT_COMP_ARG, parse_mirror_opt),
+		OPT_BOOL(0, "limited-fetch", &limited_fetch,
+			N_("fetch only the branches we build on, instead of every branch")),
 		OPT_END()
 	};
 
@@ -211,6 +214,10 @@ static int add(int argc, const char **argv, const char *prefix,
 		die(_("specifying a master branch makes no sense with --mirror"));
 	if (mirror && !(mirror & MIRROR_FETCH) && track.nr)
 		die(_("specifying branches to track makes sense only with fetch mirrors"));
+	if (limited_fetch == 1 && track.nr)
+		die(_("--limited-fetch does not make sense with -t/--track"));
+	if (limited_fetch == 1 && mirror)
+		die(_("--limited-fetch does not make sense with --mirror"));
 
 	name = argv[0];
 	url = argv[1];
@@ -230,13 +237,22 @@ static int add(int argc, const char **argv, const char *prefix,
 	repo_config_set(the_repository, buf.buf, url);
 
 	if (!mirror || mirror & MIRROR_FETCH) {
+		int use_limited_fetch = mirror == MIRROR_NONE && track.nr == 0 &&
+			limited_fetch == 1;
+
 		strbuf_reset(&buf);
-		strbuf_addf(&buf, "remote.%s.fetch", name);
-		if (track.nr == 0)
-			string_list_append(&track, "*");
-		for (size_t i = 0; i < track.nr; i++) {
-			add_branch(buf.buf, track.items[i].string,
-				   name, mirror, &buf2);
+		if (use_limited_fetch) {
+			strbuf_addf(&buf, "remote.%s.refmap", name);
+			strbuf_reset(&buf2);
+			strbuf_addf(&buf2, "+refs/heads/*:refs/remotes/%s/*", name);
+			repo_config_set(the_repository, buf.buf, buf2.buf);
+		} else {
+			strbuf_addf(&buf, "remote.%s.fetch", name);
+			if (track.nr == 0)
+				string_list_append(&track, "*");
+			for (size_t i = 0; i < track.nr; i++)
+				add_branch(buf.buf, track.items[i].string,
+					   name, mirror, &buf2);
 		}
 	}
 
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 5fbfcb0848..0168d5abfe 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -137,6 +137,22 @@ test_expect_success 'filters are listed by git remote -v only' '
 	test_grep ! "\[blob:none\]" out
 '
 
+test_expect_success '--limited-fetch works in a full repository too' '
+	test_when_finished "rm -rf full-add" &&
+	git clone --no-local one full-add &&
+	(
+		cd full-add &&
+		git remote add --limited-fetch upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.refmap &&
+		test_must_fail git config get remote.upstream.fetch
+	)
+'
+
+test_expect_success '--limited-fetch conflicts with -t' '
+	test_must_fail git remote add --limited-fetch -t main upstream ../two
+'
+
 test_expect_success 'check remote-tracking' '
 	(
 		cd test &&

Documentation/git-remote.adoc, builtin/remote.c, t/t5505-remote.sh

diff --git a/Documentation/git-remote.adoc b/Documentation/git-remote.adoc
index 4255f8b3e6..80f8a4a183 100644
--- a/Documentation/git-remote.adoc
+++ b/Documentation/git-remote.adoc
@@ -52,6 +52,11 @@ Add a remote named _<name>_ for the repository at
 _<URL>_.  The command `git fetch <name>` can then be used to create and
 update remote-tracking branches `<name>/<branch>`.
 +
+If the repository is already a shallow repository (see linkgit:git-clone[1]
+`--depth`) and neither `-t`, `--mirror` nor `--no-limited-fetch` is given,
+`--limited-fetch` is turned on by default, so that `git fetch <name>` does
+not need to negotiate history for every branch the remote has.
++
 With `-f` option, `git fetch <name>` is run immediately after
 the remote information is set up.
 +
@@ -74,7 +79,8 @@ With `--limited-fetch` option, instead of a `remote.<name>.fetch` refspec
 that tracks all branches, `remote.<name>.refmap` is set up so that a
 refspec-less `git fetch <name>` only fetches branches our local branches
 are built on. See the `--refmap` entry in linkgit:git-fetch[1] for
-details.
+details. `--no-limited-fetch` explicitly disables this, overriding the
+shallow-repository default described above.
 +
 With `-m <master>` option, a symbolic-ref `refs/remotes/<name>/HEAD` is set
 up to point at remote's _<master>_ branch. See also the set-head command.
diff --git a/builtin/remote.c b/builtin/remote.c
index f036dd5d6f..0cf1126976 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -16,6 +16,7 @@
 #include "rebase.h"
 #include "refs.h"
 #include "refspec.h"
+#include "shallow.h"
 #include "odb.h"
 #include "strvec.h"
 #include "commit-reach.h"
@@ -238,7 +239,9 @@ static int add(int argc, const char **argv, const char *prefix,
 
 	if (!mirror || mirror & MIRROR_FETCH) {
 		int use_limited_fetch = mirror == MIRROR_NONE && track.nr == 0 &&
-			limited_fetch == 1;
+			(limited_fetch == 1 ||
+			 (limited_fetch == -1 &&
+			  is_repository_shallow(the_repository)));
 
 		strbuf_reset(&buf);
 		if (use_limited_fetch) {
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 0168d5abfe..f3b5905e9e 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -137,6 +137,66 @@ test_expect_success 'filters are listed by git remote -v only' '
 	test_grep ! "\[blob:none\]" out
 '
 
+test_expect_success 'add remote -t keeps an explicit refspec in a shallow repository' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add -t main upstream ../two &&
+		test_cmp_config "+refs/heads/main:refs/remotes/upstream/main" \
+			remote.upstream.fetch
+	)
+'
+
+test_expect_success 'add remote keeps the wildcard refspec in a full repository' '
+	test_when_finished "rm -rf full-add" &&
+	git clone --no-local one full-add &&
+	(
+		cd full-add &&
+		git remote add upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.fetch
+	)
+'
+
+test_expect_success 'a remote added in a shallow repository defaults to --limited-fetch' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.refmap &&
+		test_must_fail git config get remote.upstream.fetch &&
+		git fetch upstream main &&
+		git branch --set-upstream-to=upstream/main &&
+		test_cmp_config upstream branch.main.remote &&
+		test_cmp_config refs/heads/main branch.main.merge &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success '--no-limited-fetch overrides the shallow-repository default' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add --no-limited-fetch upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.fetch &&
+		test_must_fail git config get remote.upstream.refmap
+	)
+'
+
 test_expect_success '--limited-fetch works in a full repository too' '
 	test_when_finished "rm -rf full-add" &&
 	git clone --no-local one full-add &&

Documentation/config/remote.adoc, Documentation/fetch-options.adoc, builtin/fetch.c, remote.c, remote.h, t/t5510-fetch.sh

diff --git a/Documentation/config/remote.adoc b/Documentation/config/remote.adoc
index 3a20d0f752..103eada406 100644
--- a/Documentation/config/remote.adoc
+++ b/Documentation/config/remote.adoc
@@ -33,6 +33,11 @@ remote.<name>.fetch::
 	The default set of "refspec" for linkgit:git-fetch[1]. See
 	linkgit:git-fetch[1].
 
+remote.<name>.refmap::
+	The default value of the `--refmap` option for linkgit:git-fetch[1].
+	Used to map remote refs being fetched to remote-tracking refs to
+	store. See the `--refmap` entry in linkgit:git-fetch[1].
+
 remote.<name>.push::
 	The default set of "refspec" for linkgit:git-push[1]. See
 	linkgit:git-push[1].
diff --git a/Documentation/fetch-options.adoc b/Documentation/fetch-options.adoc
index 035f780e58..538914bc6e 100644
--- a/Documentation/fetch-options.adoc
+++ b/Documentation/fetch-options.adoc
@@ -244,6 +244,9 @@ endif::git-pull[]
 	refspecs and rely entirely on the refspecs supplied as
 	command-line arguments. See section on "Configured Remote-tracking
 	Branches" for details.
++
+`remote.<name>.refmap` provides the default value for this option, the
+same way `remote.<name>.fetch` provides the default refspecs to fetch.
 
 `-t`::
 `--tags`::
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 533fdfe7d8..7651b41139 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -509,6 +509,8 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct ref *rm;
 	struct ref *ref_map = NULL;
 	struct ref **tail = &ref_map;
+	struct refspec *effective_refmap =
+		refmap.nr ? &refmap : remote ? &remote->refmap : NULL;
 
 	/* opportunistically-updated references: */
 	struct ref *orefs = NULL, **oref_tail = &orefs;
@@ -552,14 +554,14 @@ static struct ref *get_ref_map(struct remote *remote,
 		 * by ref_remove_duplicates() in favor of one of these
 		 * opportunistic entries with FETCH_HEAD_IGNORE.
 		 */
-		if (refmap.nr)
-			fetch_refspec = &refmap;
+		if (effective_refmap && effective_refmap->nr)
+			fetch_refspec = effective_refmap;
 		else
 			fetch_refspec = &remote->fetch;
 
 		for (i = 0; i < fetch_refspec->nr; i++)
 			get_fetch_map(ref_map, &fetch_refspec->items[i], &oref_tail, 1);
-	} else if (refmap.nr) {
+	} else if (effective_refmap && effective_refmap->nr) {
 		die("--refmap option is only meaningful with command-line refspec(s)");
 	} else {
 		/* Use the defaults */
diff --git a/remote.c b/remote.c
index fe62068463..017cd9d13e 100644
--- a/remote.c
+++ b/remote.c
@@ -152,6 +152,7 @@ static struct remote *make_remote(struct remote_state *remote_state,
 	ret->name = xstrndup(name, len);
 	refspec_init_push(&ret->push, the_hash_algo);
 	refspec_init_fetch(&ret->fetch, the_hash_algo);
+	refspec_init_fetch(&ret->refmap, the_hash_algo);
 	string_list_init_dup(&ret->server_options);
 	string_list_init_dup(&ret->negotiation_restrict);
 	string_list_init_dup(&ret->negotiation_include);
@@ -176,6 +177,7 @@ static void remote_clear(struct remote *remote)
 
 	refspec_clear(&remote->push);
 	refspec_clear(&remote->fetch);
+	refspec_clear(&remote->refmap);
 
 	free((char *)remote->receivepack);
 	free((char *)remote->uploadpack);
@@ -539,6 +541,12 @@ static int handle_config(const char *key, const char *value,
 			return -1;
 		refspec_append(&remote->fetch, v);
 		free(v);
+	} else if (!strcmp(subkey, "refmap")) {
+		char *v;
+		if (git_config_string(&v, key, value))
+			return -1;
+		refspec_append(&remote->refmap, v);
+		free(v);
 	} else if (!strcmp(subkey, "receivepack")) {
 		char *v;
 		if (git_config_string(&v, key, value))
@@ -988,7 +996,9 @@ void ref_push_report_free(struct ref_push_report *report)
 
 int remote_find_tracking(struct remote *remote, struct refspec_item *refspec)
 {
-	return refspec_find_match(&remote->fetch, refspec);
+	if (remote->fetch.nr)
+		return refspec_find_match(&remote->fetch, refspec);
+	return refspec_find_match(&remote->refmap, refspec);
 }
 
 static struct ref *alloc_ref_with_prefix(const char *prefix, size_t prefixlen,
diff --git a/remote.h b/remote.h
index cca02033b9..ac485a584d 100644
--- a/remote.h
+++ b/remote.h
@@ -90,6 +90,12 @@ struct remote {
 
 	struct refspec fetch;
 
+	/*
+	 * How to map refs fetched without an explicit destination into our
+	 * own namespace, the same as the --refmap command line option.
+	 */
+	struct refspec refmap;
+
 	/*
 	 * The setting for whether to fetch tags (as a separate rule from the
 	 * configured refspecs);
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index a8d38d9176..bd853d0a84 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -927,6 +927,23 @@ test_expect_success 'explicit --refmap option overrides remote.*.fetch' '
 	)
 '
 
+test_expect_success 'remote.*.refmap acts like --refmap on the command line' '
+	test_when_finished "git -C three config --unset remote.origin.refmap" &&
+	git branch -f side &&
+	git -C three config remote.origin.refmap \
+		"refs/heads/*:refs/remotes/other/*" &&
+	(
+		cd three &&
+		git update-ref refs/remotes/origin/main base-origin-main &&
+		o=$(git rev-parse --verify refs/remotes/origin/main) &&
+		git fetch origin main &&
+		n=$(git rev-parse --verify refs/remotes/origin/main) &&
+		test "$o" = "$n" &&
+		test_must_fail git rev-parse --verify refs/remotes/origin/side &&
+		git rev-parse --verify refs/remotes/other/main
+	)
+'
+
 test_expect_success 'explicitly empty --refmap option disables remote.*.fetch' '
 	git branch -f side &&
 	(

Documentation/config/remote.adoc, Documentation/fetch-options.adoc, builtin/fetch.c, remote.c, remote.h, t/meson.build, t/t5586-fetch-refmap.sh

diff --git a/Documentation/config/remote.adoc b/Documentation/config/remote.adoc
index 103eada406..7c52e443a5 100644
--- a/Documentation/config/remote.adoc
+++ b/Documentation/config/remote.adoc
@@ -36,7 +36,10 @@ remote.<name>.fetch::
 remote.<name>.refmap::
 	The default value of the `--refmap` option for linkgit:git-fetch[1].
 	Used to map remote refs being fetched to remote-tracking refs to
-	store. See the `--refmap` entry in linkgit:git-fetch[1].
+	store. If `remote.<name>.fetch` is not set either, a refspec-less
+	fetch infers what to fetch from local branches built on this
+	remote, instead of fetching every branch it has. See the
+	`--refmap` entry in linkgit:git-fetch[1].
 
 remote.<name>.push::
 	The default set of "refspec" for linkgit:git-push[1]. See
diff --git a/Documentation/fetch-options.adoc b/Documentation/fetch-options.adoc
index 538914bc6e..315daf97d7 100644
--- a/Documentation/fetch-options.adoc
+++ b/Documentation/fetch-options.adoc
@@ -245,8 +245,10 @@ endif::git-pull[]
 	command-line arguments. See section on "Configured Remote-tracking
 	Branches" for details.
 +
-`remote.<name>.refmap` provides the default value for this option, the
-same way `remote.<name>.fetch` provides the default refspecs to fetch.
+When a refmap is active (from `--refmap` or `remote.<name>.refmap`) but
+there is nothing to fetch, neither on the command line nor from
+`remote.<name>.fetch`, Git infers what to fetch from the local branches
+whose `@{upstream}` is on that remote.
 
 `-t`::
 `--tags`::
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 7651b41139..7ef2776f17 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -511,6 +511,8 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct ref **tail = &ref_map;
 	struct refspec *effective_refmap =
 		refmap.nr ? &refmap : remote ? &remote->refmap : NULL;
+	struct refspec inferred_rs;
+	int inferred_branches = 0;
 
 	/* opportunistically-updated references: */
 	struct ref *orefs = NULL, **oref_tail = &orefs;
@@ -518,15 +520,32 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct hashmap existing_refs;
 	int existing_refs_populated = 0;
 
+	refspec_init_fetch(&inferred_rs, the_hash_algo);
+
 	filter_prefetch_refspec(rs);
 	if (remote)
 		filter_prefetch_refspec(&remote->fetch);
 
+	if (!rs->nr && remote && !remote->fetch.nr &&
+	    effective_refmap && effective_refmap->nr) {
+		struct string_list tracked = STRING_LIST_INIT_DUP;
+		struct string_list_item *item;
+
+		branches_tracking_remote(remote, &tracked);
+		for_each_string_list_item(item, &tracked)
+			refspec_append(&inferred_rs, item->string);
+		string_list_clear(&tracked, 0);
+
+		rs = &inferred_rs;
+		inferred_branches = 1;
+	}
+
 	if (rs->nr) {
 		struct refspec *fetch_refspec;
 
 		for (i = 0; i < rs->nr; i++) {
-			get_fetch_map(remote_refs, &rs->items[i], &tail, 0);
+			get_fetch_map(remote_refs, &rs->items[i], &tail,
+				      inferred_branches);
 			if (rs->items[i].dst && rs->items[i].dst[0])
 				*autotags = 1;
 		}
@@ -561,6 +580,8 @@ static struct ref *get_ref_map(struct remote *remote,
 
 		for (i = 0; i < fetch_refspec->nr; i++)
 			get_fetch_map(ref_map, &fetch_refspec->items[i], &oref_tail, 1);
+	} else if (inferred_branches) {
+		/* Already fully handled above. */
 	} else if (effective_refmap && effective_refmap->nr) {
 		die("--refmap option is only meaningful with command-line refspec(s)");
 	} else {
@@ -656,6 +677,7 @@ static struct ref *get_ref_map(struct remote *remote,
 	if (existing_refs_populated)
 		hashmap_clear_and_free(&existing_refs, struct refname_hash_entry, ent);
 
+	refspec_clear(&inferred_rs);
 	return ref_map;
 }
 
@@ -1960,15 +1982,30 @@ static int do_fetch(struct transport *transport,
 		refspec_ref_prefixes(rs, &transport_ls_refs_options.ref_prefixes);
 	} else {
 		struct branch *branch = branch_get(NULL);
-
-		if (transport->remote->fetch.nr) {
+		int tracks_this_remote = branch && branch_has_merge_config(branch) &&
+			!strcmp(branch->remote_name, transport->remote->name);
+		struct refspec *effective_refmap = refmap.nr ? &refmap :
+			&transport->remote->refmap;
+		int inferred_branches = !transport->remote->fetch.nr &&
+			effective_refmap->nr;
+
+		if (inferred_branches) {
+			struct string_list tracked = STRING_LIST_INIT_DUP;
+			struct string_list_item *item;
+
+			branches_tracking_remote(transport->remote, &tracked);
+			for_each_string_list_item(item, &tracked)
+				strvec_push(&transport_ls_refs_options.ref_prefixes,
+					    item->string);
+			string_list_clear(&tracked, 0);
+		} else if (transport->remote->fetch.nr) {
 			refspec_ref_prefixes(&transport->remote->fetch,
 					     &transport_ls_refs_options.ref_prefixes);
-			if (follow_remote_head != FOLLOW_REMOTE_NEVER)
-				do_set_head = 1;
 		}
-		if (branch && branch_has_merge_config(branch) &&
-		    !strcmp(branch->remote_name, transport->remote->name)) {
+		if ((transport->remote->fetch.nr || inferred_branches) &&
+		    follow_remote_head != FOLLOW_REMOTE_NEVER)
+			do_set_head = 1;
+		if (tracks_this_remote) {
 			int i;
 			for (i = 0; i < branch->merge_nr; i++) {
 				strvec_push(&transport_ls_refs_options.ref_prefixes,
@@ -2009,6 +2046,7 @@ static int do_fetch(struct transport *transport,
 
 	ref_map = get_ref_map(transport->remote, remote_refs, rs,
 			      tags, &autotags);
+
 	if (!update_head_ok)
 		check_not_current_branch(ref_map);
 
diff --git a/remote.c b/remote.c
index 017cd9d13e..a5deb9b929 100644
--- a/remote.c
+++ b/remote.c
@@ -1884,6 +1884,35 @@ int branch_merge_matches(struct branch *branch,
 	return refname_match(branch->merge[i]->src, refname);
 }
 
+struct branches_tracking_remote_cb_data {
+	struct remote *remote;
+	struct string_list *tracked;
+};
+
+static int add_if_tracking_remote(const struct reference *ref, void *cb_data)
+{
+	struct branches_tracking_remote_cb_data *data = cb_data;
+	struct branch *branch;
+
+	branch = branch_get(ref->name);
+	if (!branch_has_merge_config(branch) ||
+	    strcmp(branch->remote_name, data->remote->name))
+		return 0;
+
+	for (int i = 0; i < branch->merge_nr; i++)
+		string_list_insert(data->tracked, branch->merge[i]->src);
+
+	return 0;
+}
+
+void branches_tracking_remote(struct remote *remote, struct string_list *tracked)
+{
+	struct branches_tracking_remote_cb_data data = { remote, tracked };
+
+	refs_for_each_branch_ref(get_main_ref_store(the_repository),
+				  add_if_tracking_remote, &data);
+}
+
 __attribute__((format (printf,2,3)))
 static char *error_buf(struct strbuf *err, const char *fmt, ...)
 {
diff --git a/remote.h b/remote.h
index ac485a584d..da6c3ef53a 100644
--- a/remote.h
+++ b/remote.h
@@ -359,6 +359,9 @@ int branch_has_merge_config(struct branch *branch);
 
 int branch_merge_matches(struct branch *, int n, const char *);
 
+/* fills tracked with the refname of every local branch's upstream on remote */
+void branches_tracking_remote(struct remote *remote, struct string_list *tracked);
+
 /* list of the remote in a group as configured */
 struct remote_group_data {
 	const char *name;
diff --git a/t/meson.build b/t/meson.build
index 3ca7b27104..a1c7465c2b 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -728,6 +728,7 @@ integration_tests = [
   't5582-fetch-negative-refspec.sh',
   't5583-push-branches.sh',
   't5584-http-429-retry.sh',
+  't5586-fetch-refmap.sh',
   't5600-clone-fail-cleanup.sh',
   't5601-clone.sh',
   't5602-clone-remote-exec.sh',
diff --git a/t/t5586-fetch-refmap.sh b/t/t5586-fetch-refmap.sh
new file mode 100755
index 0000000000..b81fc48cbe
--- /dev/null
+++ b/t/t5586-fetch-refmap.sh
@@ -0,0 +1,119 @@
+#!/bin/sh
+
+test_description='"git fetch" with a remote.<name>.refmap but no remote.<name>.fetch
+
+When a remote has a refmap configured but no fetch refspec, a
+refspec-less fetch infers what to fetch from the local branches whose
+@{upstream} is on that remote.
+'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit main-1 &&
+	test_commit main-2 &&
+	git checkout -b side main-1 &&
+	test_commit side-1 &&
+	git checkout -b next main-1 &&
+	test_commit next-1 &&
+	git checkout main
+'
+
+test_expect_success 'clone shallow and single-branch, then add a second remote' '
+	git clone --no-local --depth=1 --branch main --single-branch . client &&
+	(
+		cd client &&
+		git remote add upstream .. &&
+		test_might_fail git config unset remote.upstream.fetch &&
+		git config remote.upstream.refmap \
+			"+refs/heads/*:refs/remotes/upstream/*"
+	)
+'
+
+test_expect_success 'a bare fetch needs nothing until a branch is tracked' '
+	(
+		cd client &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		test_must_be_empty actual
+	)
+'
+
+test_expect_success 'an explicit one-time fetch lets a branch be tracked' '
+	(
+		cd client &&
+		git fetch upstream main &&
+		git branch --set-upstream-to=upstream/main &&
+		test_cmp_config upstream branch.main.remote &&
+		test_cmp_config refs/heads/main branch.main.merge
+	)
+'
+
+test_expect_success 'a branch checked out from a one-time fetch is kept updated by later plain fetches' '
+	(
+		cd client &&
+		git fetch upstream side:refs/remotes/upstream/side &&
+		git branch side-topic upstream/side
+	) &&
+	git checkout side &&
+	test_commit side-2 &&
+	git checkout main &&
+	(
+		cd client &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual &&
+		git rev-parse refs/remotes/upstream/side >actual-oid &&
+		git -C .. rev-parse side >expect-oid &&
+		test_cmp expect-oid actual-oid
+	)
+'
+
+test_expect_success 'a second branch tracking the same upstream branch does not fetch it twice' '
+	(
+		cd client &&
+		git branch side-topic-2 upstream/side &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'a branch tracking a different remote is not fetched from upstream' '
+	(
+		cd client &&
+		git remote add other .. &&
+		git fetch other next:refs/remotes/other/next &&
+		git branch next-topic other/next &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'git remote show does not choke on a refmap-only remote' '
+	(
+		cd client &&
+		git remote show upstream
+	)
+'
+
+test_done

Documentation/git-remote.adoc, builtin/remote.c, t/t5505-remote.sh

diff --git a/Documentation/git-remote.adoc b/Documentation/git-remote.adoc
index eaae30aa88..4255f8b3e6 100644
--- a/Documentation/git-remote.adoc
+++ b/Documentation/git-remote.adoc
@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 [synopsis]
 git remote [-v | --verbose]
-git remote add [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=(fetch|push)] <name> <URL>
+git remote add [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=(fetch|push)] [--[no-]limited-fetch] <name> <URL>
 git remote rename [--[no-]progress] <old> <new>
 git remote remove <name>
 git remote set-head <name> (-a | --auto | -d | --delete | <branch>)
@@ -70,6 +70,12 @@ the `refs/remotes/<name>/` namespace, a refspec to track only _<branch>_
 is created.  You can give more than one `-t <branch>` to track
 multiple branches without grabbing all branches.
 +
+With `--limited-fetch` option, instead of a `remote.<name>.fetch` refspec
+that tracks all branches, `remote.<name>.refmap` is set up so that a
+refspec-less `git fetch <name>` only fetches branches our local branches
+are built on. See the `--refmap` entry in linkgit:git-fetch[1] for
+details.
++
 With `-m <master>` option, a symbolic-ref `refs/remotes/<name>/HEAD` is set
 up to point at remote's _<master>_ branch. See also the set-head command.
 +
diff --git a/builtin/remote.c b/builtin/remote.c
index de989ea3ba..f036dd5d6f 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -179,6 +179,7 @@ static int add(int argc, const char **argv, const char *prefix,
 {
 	int fetch = 0, fetch_tags = TAGS_DEFAULT;
 	unsigned mirror = MIRROR_NONE;
+	int limited_fetch = -1; /* unspecified */
 	struct string_list track = STRING_LIST_INIT_NODUP;
 	const char *master = NULL;
 	struct remote *remote;
@@ -198,6 +199,8 @@ static int add(int argc, const char **argv, const char *prefix,
 		OPT_CALLBACK_F(0, "mirror", &mirror, "(push|fetch)",
 			N_("set up remote as a mirror to push to or fetch from"),
 			PARSE_OPT_OPTARG | PARSE_OPT_COMP_ARG, parse_mirror_opt),
+		OPT_BOOL(0, "limited-fetch", &limited_fetch,
+			N_("fetch only the branches we build on, instead of every branch")),
 		OPT_END()
 	};
 
@@ -211,6 +214,10 @@ static int add(int argc, const char **argv, const char *prefix,
 		die(_("specifying a master branch makes no sense with --mirror"));
 	if (mirror && !(mirror & MIRROR_FETCH) && track.nr)
 		die(_("specifying branches to track makes sense only with fetch mirrors"));
+	if (limited_fetch == 1 && track.nr)
+		die(_("--limited-fetch does not make sense with -t/--track"));
+	if (limited_fetch == 1 && mirror)
+		die(_("--limited-fetch does not make sense with --mirror"));
 
 	name = argv[0];
 	url = argv[1];
@@ -230,13 +237,22 @@ static int add(int argc, const char **argv, const char *prefix,
 	repo_config_set(the_repository, buf.buf, url);
 
 	if (!mirror || mirror & MIRROR_FETCH) {
+		int use_limited_fetch = mirror == MIRROR_NONE && track.nr == 0 &&
+			limited_fetch == 1;
+
 		strbuf_reset(&buf);
-		strbuf_addf(&buf, "remote.%s.fetch", name);
-		if (track.nr == 0)
-			string_list_append(&track, "*");
-		for (size_t i = 0; i < track.nr; i++) {
-			add_branch(buf.buf, track.items[i].string,
-				   name, mirror, &buf2);
+		if (use_limited_fetch) {
+			strbuf_addf(&buf, "remote.%s.refmap", name);
+			strbuf_reset(&buf2);
+			strbuf_addf(&buf2, "+refs/heads/*:refs/remotes/%s/*", name);
+			repo_config_set(the_repository, buf.buf, buf2.buf);
+		} else {
+			strbuf_addf(&buf, "remote.%s.fetch", name);
+			if (track.nr == 0)
+				string_list_append(&track, "*");
+			for (size_t i = 0; i < track.nr; i++)
+				add_branch(buf.buf, track.items[i].string,
+					   name, mirror, &buf2);
 		}
 	}
 
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 5fbfcb0848..0168d5abfe 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -137,6 +137,22 @@ test_expect_success 'filters are listed by git remote -v only' '
 	test_grep ! "\[blob:none\]" out
 '
 
+test_expect_success '--limited-fetch works in a full repository too' '
+	test_when_finished "rm -rf full-add" &&
+	git clone --no-local one full-add &&
+	(
+		cd full-add &&
+		git remote add --limited-fetch upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.refmap &&
+		test_must_fail git config get remote.upstream.fetch
+	)
+'
+
+test_expect_success '--limited-fetch conflicts with -t' '
+	test_must_fail git remote add --limited-fetch -t main upstream ../two
+'
+
 test_expect_success 'check remote-tracking' '
 	(
 		cd test &&

Documentation/git-remote.adoc, builtin/remote.c, t/t5505-remote.sh

diff --git a/Documentation/git-remote.adoc b/Documentation/git-remote.adoc
index 4255f8b3e6..80f8a4a183 100644
--- a/Documentation/git-remote.adoc
+++ b/Documentation/git-remote.adoc
@@ -52,6 +52,11 @@ Add a remote named _<name>_ for the repository at
 _<URL>_.  The command `git fetch <name>` can then be used to create and
 update remote-tracking branches `<name>/<branch>`.
 +
+If the repository is already a shallow repository (see linkgit:git-clone[1]
+`--depth`) and neither `-t`, `--mirror` nor `--no-limited-fetch` is given,
+`--limited-fetch` is turned on by default, so that `git fetch <name>` does
+not need to negotiate history for every branch the remote has.
++
 With `-f` option, `git fetch <name>` is run immediately after
 the remote information is set up.
 +
@@ -74,7 +79,8 @@ With `--limited-fetch` option, instead of a `remote.<name>.fetch` refspec
 that tracks all branches, `remote.<name>.refmap` is set up so that a
 refspec-less `git fetch <name>` only fetches branches our local branches
 are built on. See the `--refmap` entry in linkgit:git-fetch[1] for
-details.
+details. `--no-limited-fetch` explicitly disables this, overriding the
+shallow-repository default described above.
 +
 With `-m <master>` option, a symbolic-ref `refs/remotes/<name>/HEAD` is set
 up to point at remote's _<master>_ branch. See also the set-head command.
diff --git a/builtin/remote.c b/builtin/remote.c
index f036dd5d6f..0cf1126976 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -16,6 +16,7 @@
 #include "rebase.h"
 #include "refs.h"
 #include "refspec.h"
+#include "shallow.h"
 #include "odb.h"
 #include "strvec.h"
 #include "commit-reach.h"
@@ -238,7 +239,9 @@ static int add(int argc, const char **argv, const char *prefix,
 
 	if (!mirror || mirror & MIRROR_FETCH) {
 		int use_limited_fetch = mirror == MIRROR_NONE && track.nr == 0 &&
-			limited_fetch == 1;
+			(limited_fetch == 1 ||
+			 (limited_fetch == -1 &&
+			  is_repository_shallow(the_repository)));
 
 		strbuf_reset(&buf);
 		if (use_limited_fetch) {
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 0168d5abfe..f3b5905e9e 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -137,6 +137,66 @@ test_expect_success 'filters are listed by git remote -v only' '
 	test_grep ! "\[blob:none\]" out
 '
 
+test_expect_success 'add remote -t keeps an explicit refspec in a shallow repository' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add -t main upstream ../two &&
+		test_cmp_config "+refs/heads/main:refs/remotes/upstream/main" \
+			remote.upstream.fetch
+	)
+'
+
+test_expect_success 'add remote keeps the wildcard refspec in a full repository' '
+	test_when_finished "rm -rf full-add" &&
+	git clone --no-local one full-add &&
+	(
+		cd full-add &&
+		git remote add upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.fetch
+	)
+'
+
+test_expect_success 'a remote added in a shallow repository defaults to --limited-fetch' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.refmap &&
+		test_must_fail git config get remote.upstream.fetch &&
+		git fetch upstream main &&
+		git branch --set-upstream-to=upstream/main &&
+		test_cmp_config upstream branch.main.remote &&
+		test_cmp_config refs/heads/main branch.main.merge &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success '--no-limited-fetch overrides the shallow-repository default' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add --no-limited-fetch upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.fetch &&
+		test_must_fail git config get remote.upstream.refmap
+	)
+'
+
 test_expect_success '--limited-fetch works in a full repository too' '
 	test_when_finished "rm -rf full-add" &&
 	git clone --no-local one full-add &&

Documentation/config/remote.adoc, Documentation/fetch-options.adoc, builtin/fetch.c, remote.c, remote.h, t/t5510-fetch.sh

diff --git a/Documentation/config/remote.adoc b/Documentation/config/remote.adoc
index 3a20d0f752..103eada406 100644
--- a/Documentation/config/remote.adoc
+++ b/Documentation/config/remote.adoc
@@ -33,6 +33,11 @@ remote.<name>.fetch::
 	The default set of "refspec" for linkgit:git-fetch[1]. See
 	linkgit:git-fetch[1].
 
+remote.<name>.refmap::
+	The default value of the `--refmap` option for linkgit:git-fetch[1].
+	Used to map remote refs being fetched to remote-tracking refs to
+	store. See the `--refmap` entry in linkgit:git-fetch[1].
+
 remote.<name>.push::
 	The default set of "refspec" for linkgit:git-push[1]. See
 	linkgit:git-push[1].
diff --git a/Documentation/fetch-options.adoc b/Documentation/fetch-options.adoc
index 035f780e58..538914bc6e 100644
--- a/Documentation/fetch-options.adoc
+++ b/Documentation/fetch-options.adoc
@@ -244,6 +244,9 @@ endif::git-pull[]
 	refspecs and rely entirely on the refspecs supplied as
 	command-line arguments. See section on "Configured Remote-tracking
 	Branches" for details.
++
+`remote.<name>.refmap` provides the default value for this option, the
+same way `remote.<name>.fetch` provides the default refspecs to fetch.
 
 `-t`::
 `--tags`::
diff --git a/builtin/fetch.c b/builtin/fetch.c
index b2decc6cfd..04d0a78ecf 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -509,6 +509,8 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct ref *rm;
 	struct ref *ref_map = NULL;
 	struct ref **tail = &ref_map;
+	struct refspec *effective_refmap =
+		refmap.nr ? &refmap : remote ? &remote->refmap : NULL;
 
 	/* opportunistically-updated references: */
 	struct ref *orefs = NULL, **oref_tail = &orefs;
@@ -552,14 +554,14 @@ static struct ref *get_ref_map(struct remote *remote,
 		 * by ref_remove_duplicates() in favor of one of these
 		 * opportunistic entries with FETCH_HEAD_IGNORE.
 		 */
-		if (refmap.nr)
-			fetch_refspec = &refmap;
+		if (effective_refmap && effective_refmap->nr)
+			fetch_refspec = effective_refmap;
 		else
 			fetch_refspec = &remote->fetch;
 
 		for (i = 0; i < fetch_refspec->nr; i++)
 			get_fetch_map(ref_map, &fetch_refspec->items[i], &oref_tail, 1);
-	} else if (refmap.nr) {
+	} else if (effective_refmap && effective_refmap->nr) {
 		die("--refmap option is only meaningful with command-line refspec(s)");
 	} else {
 		/* Use the defaults */
diff --git a/remote.c b/remote.c
index fe62068463..017cd9d13e 100644
--- a/remote.c
+++ b/remote.c
@@ -152,6 +152,7 @@ static struct remote *make_remote(struct remote_state *remote_state,
 	ret->name = xstrndup(name, len);
 	refspec_init_push(&ret->push, the_hash_algo);
 	refspec_init_fetch(&ret->fetch, the_hash_algo);
+	refspec_init_fetch(&ret->refmap, the_hash_algo);
 	string_list_init_dup(&ret->server_options);
 	string_list_init_dup(&ret->negotiation_restrict);
 	string_list_init_dup(&ret->negotiation_include);
@@ -176,6 +177,7 @@ static void remote_clear(struct remote *remote)
 
 	refspec_clear(&remote->push);
 	refspec_clear(&remote->fetch);
+	refspec_clear(&remote->refmap);
 
 	free((char *)remote->receivepack);
 	free((char *)remote->uploadpack);
@@ -539,6 +541,12 @@ static int handle_config(const char *key, const char *value,
 			return -1;
 		refspec_append(&remote->fetch, v);
 		free(v);
+	} else if (!strcmp(subkey, "refmap")) {
+		char *v;
+		if (git_config_string(&v, key, value))
+			return -1;
+		refspec_append(&remote->refmap, v);
+		free(v);
 	} else if (!strcmp(subkey, "receivepack")) {
 		char *v;
 		if (git_config_string(&v, key, value))
@@ -988,7 +996,9 @@ void ref_push_report_free(struct ref_push_report *report)
 
 int remote_find_tracking(struct remote *remote, struct refspec_item *refspec)
 {
-	return refspec_find_match(&remote->fetch, refspec);
+	if (remote->fetch.nr)
+		return refspec_find_match(&remote->fetch, refspec);
+	return refspec_find_match(&remote->refmap, refspec);
 }
 
 static struct ref *alloc_ref_with_prefix(const char *prefix, size_t prefixlen,
diff --git a/remote.h b/remote.h
index cca02033b9..ac485a584d 100644
--- a/remote.h
+++ b/remote.h
@@ -90,6 +90,12 @@ struct remote {
 
 	struct refspec fetch;
 
+	/*
+	 * How to map refs fetched without an explicit destination into our
+	 * own namespace, the same as the --refmap command line option.
+	 */
+	struct refspec refmap;
+
 	/*
 	 * The setting for whether to fetch tags (as a separate rule from the
 	 * configured refspecs);
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 300bd5396d..36fa9319e1 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -927,6 +927,23 @@ test_expect_success 'explicit --refmap option overrides remote.*.fetch' '
 	)
 '
 
+test_expect_success 'remote.*.refmap acts like --refmap on the command line' '
+	test_when_finished "git -C three config --unset remote.origin.refmap" &&
+	git branch -f side &&
+	git -C three config remote.origin.refmap \
+		"refs/heads/*:refs/remotes/other/*" &&
+	(
+		cd three &&
+		git update-ref refs/remotes/origin/main base-origin-main &&
+		o=$(git rev-parse --verify refs/remotes/origin/main) &&
+		git fetch origin main &&
+		n=$(git rev-parse --verify refs/remotes/origin/main) &&
+		test "$o" = "$n" &&
+		test_must_fail git rev-parse --verify refs/remotes/origin/side &&
+		git rev-parse --verify refs/remotes/other/main
+	)
+'
+
 test_expect_success 'explicitly empty --refmap option disables remote.*.fetch' '
 	git branch -f side &&
 	(

Documentation/config/remote.adoc, Documentation/fetch-options.adoc, builtin/fetch.c, remote.c, remote.h, t/meson.build, t/t5586-fetch-refmap.sh

diff --git a/Documentation/config/remote.adoc b/Documentation/config/remote.adoc
index 103eada406..7c52e443a5 100644
--- a/Documentation/config/remote.adoc
+++ b/Documentation/config/remote.adoc
@@ -36,7 +36,10 @@ remote.<name>.fetch::
 remote.<name>.refmap::
 	The default value of the `--refmap` option for linkgit:git-fetch[1].
 	Used to map remote refs being fetched to remote-tracking refs to
-	store. See the `--refmap` entry in linkgit:git-fetch[1].
+	store. If `remote.<name>.fetch` is not set either, a refspec-less
+	fetch infers what to fetch from local branches built on this
+	remote, instead of fetching every branch it has. See the
+	`--refmap` entry in linkgit:git-fetch[1].
 
 remote.<name>.push::
 	The default set of "refspec" for linkgit:git-push[1]. See
diff --git a/Documentation/fetch-options.adoc b/Documentation/fetch-options.adoc
index 538914bc6e..315daf97d7 100644
--- a/Documentation/fetch-options.adoc
+++ b/Documentation/fetch-options.adoc
@@ -245,8 +245,10 @@ endif::git-pull[]
 	command-line arguments. See section on "Configured Remote-tracking
 	Branches" for details.
 +
-`remote.<name>.refmap` provides the default value for this option, the
-same way `remote.<name>.fetch` provides the default refspecs to fetch.
+When a refmap is active (from `--refmap` or `remote.<name>.refmap`) but
+there is nothing to fetch, neither on the command line nor from
+`remote.<name>.fetch`, Git infers what to fetch from the local branches
+whose `@{upstream}` is on that remote.
 
 `-t`::
 `--tags`::
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 04d0a78ecf..e928f5d7e0 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -511,6 +511,8 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct ref **tail = &ref_map;
 	struct refspec *effective_refmap =
 		refmap.nr ? &refmap : remote ? &remote->refmap : NULL;
+	struct refspec inferred_rs;
+	int inferred_branches = 0;
 
 	/* opportunistically-updated references: */
 	struct ref *orefs = NULL, **oref_tail = &orefs;
@@ -518,15 +520,32 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct hashmap existing_refs;
 	int existing_refs_populated = 0;
 
+	refspec_init_fetch(&inferred_rs, the_hash_algo);
+
 	filter_prefetch_refspec(rs);
 	if (remote)
 		filter_prefetch_refspec(&remote->fetch);
 
+	if (!rs->nr && remote && !remote->fetch.nr &&
+	    effective_refmap && effective_refmap->nr) {
+		struct string_list tracked = STRING_LIST_INIT_DUP;
+		struct string_list_item *item;
+
+		branches_tracking_remote(remote, &tracked);
+		for_each_string_list_item(item, &tracked)
+			refspec_append(&inferred_rs, item->string);
+		string_list_clear(&tracked, 0);
+
+		rs = &inferred_rs;
+		inferred_branches = 1;
+	}
+
 	if (rs->nr) {
 		struct refspec *fetch_refspec;
 
 		for (i = 0; i < rs->nr; i++) {
-			get_fetch_map(remote_refs, &rs->items[i], &tail, 0);
+			get_fetch_map(remote_refs, &rs->items[i], &tail,
+				      inferred_branches);
 			if (rs->items[i].dst && rs->items[i].dst[0])
 				*autotags = 1;
 		}
@@ -561,6 +580,8 @@ static struct ref *get_ref_map(struct remote *remote,
 
 		for (i = 0; i < fetch_refspec->nr; i++)
 			get_fetch_map(ref_map, &fetch_refspec->items[i], &oref_tail, 1);
+	} else if (inferred_branches) {
+		/* Already fully handled above. */
 	} else if (effective_refmap && effective_refmap->nr) {
 		die("--refmap option is only meaningful with command-line refspec(s)");
 	} else {
@@ -656,6 +677,7 @@ static struct ref *get_ref_map(struct remote *remote,
 	if (existing_refs_populated)
 		hashmap_clear_and_free(&existing_refs, struct refname_hash_entry, ent);
 
+	refspec_clear(&inferred_rs);
 	return ref_map;
 }
 
@@ -1960,15 +1982,30 @@ static int do_fetch(struct transport *transport,
 		refspec_ref_prefixes(rs, &transport_ls_refs_options.ref_prefixes);
 	} else {
 		struct branch *branch = branch_get(NULL);
-
-		if (transport->remote->fetch.nr) {
+		int tracks_this_remote = branch && branch_has_merge_config(branch) &&
+			!strcmp(branch->remote_name, transport->remote->name);
+		struct refspec *effective_refmap = refmap.nr ? &refmap :
+			&transport->remote->refmap;
+		int inferred_branches = !transport->remote->fetch.nr &&
+			effective_refmap->nr;
+
+		if (inferred_branches) {
+			struct string_list tracked = STRING_LIST_INIT_DUP;
+			struct string_list_item *item;
+
+			branches_tracking_remote(transport->remote, &tracked);
+			for_each_string_list_item(item, &tracked)
+				strvec_push(&transport_ls_refs_options.ref_prefixes,
+					    item->string);
+			string_list_clear(&tracked, 0);
+		} else if (transport->remote->fetch.nr) {
 			refspec_ref_prefixes(&transport->remote->fetch,
 					     &transport_ls_refs_options.ref_prefixes);
-			if (follow_remote_head != FOLLOW_REMOTE_NEVER)
-				do_set_head = 1;
 		}
-		if (branch && branch_has_merge_config(branch) &&
-		    !strcmp(branch->remote_name, transport->remote->name)) {
+		if ((transport->remote->fetch.nr || inferred_branches) &&
+		    follow_remote_head != FOLLOW_REMOTE_NEVER)
+			do_set_head = 1;
+		if (tracks_this_remote) {
 			int i;
 			for (i = 0; i < branch->merge_nr; i++) {
 				strvec_push(&transport_ls_refs_options.ref_prefixes,
@@ -2009,6 +2046,7 @@ static int do_fetch(struct transport *transport,
 
 	ref_map = get_ref_map(transport->remote, remote_refs, rs,
 			      tags, &autotags);
+
 	if (!update_head_ok)
 		check_not_current_branch(ref_map);
 
diff --git a/remote.c b/remote.c
index 017cd9d13e..a5deb9b929 100644
--- a/remote.c
+++ b/remote.c
@@ -1884,6 +1884,35 @@ int branch_merge_matches(struct branch *branch,
 	return refname_match(branch->merge[i]->src, refname);
 }
 
+struct branches_tracking_remote_cb_data {
+	struct remote *remote;
+	struct string_list *tracked;
+};
+
+static int add_if_tracking_remote(const struct reference *ref, void *cb_data)
+{
+	struct branches_tracking_remote_cb_data *data = cb_data;
+	struct branch *branch;
+
+	branch = branch_get(ref->name);
+	if (!branch_has_merge_config(branch) ||
+	    strcmp(branch->remote_name, data->remote->name))
+		return 0;
+
+	for (int i = 0; i < branch->merge_nr; i++)
+		string_list_insert(data->tracked, branch->merge[i]->src);
+
+	return 0;
+}
+
+void branches_tracking_remote(struct remote *remote, struct string_list *tracked)
+{
+	struct branches_tracking_remote_cb_data data = { remote, tracked };
+
+	refs_for_each_branch_ref(get_main_ref_store(the_repository),
+				  add_if_tracking_remote, &data);
+}
+
 __attribute__((format (printf,2,3)))
 static char *error_buf(struct strbuf *err, const char *fmt, ...)
 {
diff --git a/remote.h b/remote.h
index ac485a584d..da6c3ef53a 100644
--- a/remote.h
+++ b/remote.h
@@ -359,6 +359,9 @@ int branch_has_merge_config(struct branch *branch);
 
 int branch_merge_matches(struct branch *, int n, const char *);
 
+/* fills tracked with the refname of every local branch's upstream on remote */
+void branches_tracking_remote(struct remote *remote, struct string_list *tracked);
+
 /* list of the remote in a group as configured */
 struct remote_group_data {
 	const char *name;
diff --git a/t/meson.build b/t/meson.build
index f65eb04684..e287a6b947 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -730,6 +730,7 @@ integration_tests = [
   't5582-fetch-negative-refspec.sh',
   't5583-push-branches.sh',
   't5584-http-429-retry.sh',
+  't5586-fetch-refmap.sh',
   't5600-clone-fail-cleanup.sh',
   't5601-clone.sh',
   't5602-clone-remote-exec.sh',
diff --git a/t/t5586-fetch-refmap.sh b/t/t5586-fetch-refmap.sh
new file mode 100755
index 0000000000..b81fc48cbe
--- /dev/null
+++ b/t/t5586-fetch-refmap.sh
@@ -0,0 +1,119 @@
+#!/bin/sh
+
+test_description='"git fetch" with a remote.<name>.refmap but no remote.<name>.fetch
+
+When a remote has a refmap configured but no fetch refspec, a
+refspec-less fetch infers what to fetch from the local branches whose
+@{upstream} is on that remote.
+'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit main-1 &&
+	test_commit main-2 &&
+	git checkout -b side main-1 &&
+	test_commit side-1 &&
+	git checkout -b next main-1 &&
+	test_commit next-1 &&
+	git checkout main
+'
+
+test_expect_success 'clone shallow and single-branch, then add a second remote' '
+	git clone --no-local --depth=1 --branch main --single-branch . client &&
+	(
+		cd client &&
+		git remote add upstream .. &&
+		test_might_fail git config unset remote.upstream.fetch &&
+		git config remote.upstream.refmap \
+			"+refs/heads/*:refs/remotes/upstream/*"
+	)
+'
+
+test_expect_success 'a bare fetch needs nothing until a branch is tracked' '
+	(
+		cd client &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		test_must_be_empty actual
+	)
+'
+
+test_expect_success 'an explicit one-time fetch lets a branch be tracked' '
+	(
+		cd client &&
+		git fetch upstream main &&
+		git branch --set-upstream-to=upstream/main &&
+		test_cmp_config upstream branch.main.remote &&
+		test_cmp_config refs/heads/main branch.main.merge
+	)
+'
+
+test_expect_success 'a branch checked out from a one-time fetch is kept updated by later plain fetches' '
+	(
+		cd client &&
+		git fetch upstream side:refs/remotes/upstream/side &&
+		git branch side-topic upstream/side
+	) &&
+	git checkout side &&
+	test_commit side-2 &&
+	git checkout main &&
+	(
+		cd client &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual &&
+		git rev-parse refs/remotes/upstream/side >actual-oid &&
+		git -C .. rev-parse side >expect-oid &&
+		test_cmp expect-oid actual-oid
+	)
+'
+
+test_expect_success 'a second branch tracking the same upstream branch does not fetch it twice' '
+	(
+		cd client &&
+		git branch side-topic-2 upstream/side &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'a branch tracking a different remote is not fetched from upstream' '
+	(
+		cd client &&
+		git remote add other .. &&
+		git fetch other next:refs/remotes/other/next &&
+		git branch next-topic other/next &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		refs/remotes/upstream/side
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'git remote show does not choke on a refmap-only remote' '
+	(
+		cd client &&
+		git remote show upstream
+	)
+'
+
+test_done

Documentation/git-remote.adoc, builtin/remote.c, t/t5505-remote.sh

diff --git a/Documentation/git-remote.adoc b/Documentation/git-remote.adoc
index eaae30aa88..4255f8b3e6 100644
--- a/Documentation/git-remote.adoc
+++ b/Documentation/git-remote.adoc
@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 [synopsis]
 git remote [-v | --verbose]
-git remote add [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=(fetch|push)] <name> <URL>
+git remote add [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=(fetch|push)] [--[no-]limited-fetch] <name> <URL>
 git remote rename [--[no-]progress] <old> <new>
 git remote remove <name>
 git remote set-head <name> (-a | --auto | -d | --delete | <branch>)
@@ -70,6 +70,12 @@ the `refs/remotes/<name>/` namespace, a refspec to track only _<branch>_
 is created.  You can give more than one `-t <branch>` to track
 multiple branches without grabbing all branches.
 +
+With `--limited-fetch` option, instead of a `remote.<name>.fetch` refspec
+that tracks all branches, `remote.<name>.refmap` is set up so that a
+refspec-less `git fetch <name>` only fetches branches our local branches
+are built on. See the `--refmap` entry in linkgit:git-fetch[1] for
+details.
++
 With `-m <master>` option, a symbolic-ref `refs/remotes/<name>/HEAD` is set
 up to point at remote's _<master>_ branch. See also the set-head command.
 +
diff --git a/builtin/remote.c b/builtin/remote.c
index de989ea3ba..f036dd5d6f 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -179,6 +179,7 @@ static int add(int argc, const char **argv, const char *prefix,
 {
 	int fetch = 0, fetch_tags = TAGS_DEFAULT;
 	unsigned mirror = MIRROR_NONE;
+	int limited_fetch = -1; /* unspecified */
 	struct string_list track = STRING_LIST_INIT_NODUP;
 	const char *master = NULL;
 	struct remote *remote;
@@ -198,6 +199,8 @@ static int add(int argc, const char **argv, const char *prefix,
 		OPT_CALLBACK_F(0, "mirror", &mirror, "(push|fetch)",
 			N_("set up remote as a mirror to push to or fetch from"),
 			PARSE_OPT_OPTARG | PARSE_OPT_COMP_ARG, parse_mirror_opt),
+		OPT_BOOL(0, "limited-fetch", &limited_fetch,
+			N_("fetch only the branches we build on, instead of every branch")),
 		OPT_END()
 	};
 
@@ -211,6 +214,10 @@ static int add(int argc, const char **argv, const char *prefix,
 		die(_("specifying a master branch makes no sense with --mirror"));
 	if (mirror && !(mirror & MIRROR_FETCH) && track.nr)
 		die(_("specifying branches to track makes sense only with fetch mirrors"));
+	if (limited_fetch == 1 && track.nr)
+		die(_("--limited-fetch does not make sense with -t/--track"));
+	if (limited_fetch == 1 && mirror)
+		die(_("--limited-fetch does not make sense with --mirror"));
 
 	name = argv[0];
 	url = argv[1];
@@ -230,13 +237,22 @@ static int add(int argc, const char **argv, const char *prefix,
 	repo_config_set(the_repository, buf.buf, url);
 
 	if (!mirror || mirror & MIRROR_FETCH) {
+		int use_limited_fetch = mirror == MIRROR_NONE && track.nr == 0 &&
+			limited_fetch == 1;
+
 		strbuf_reset(&buf);
-		strbuf_addf(&buf, "remote.%s.fetch", name);
-		if (track.nr == 0)
-			string_list_append(&track, "*");
-		for (size_t i = 0; i < track.nr; i++) {
-			add_branch(buf.buf, track.items[i].string,
-				   name, mirror, &buf2);
+		if (use_limited_fetch) {
+			strbuf_addf(&buf, "remote.%s.refmap", name);
+			strbuf_reset(&buf2);
+			strbuf_addf(&buf2, "+refs/heads/*:refs/remotes/%s/*", name);
+			repo_config_set(the_repository, buf.buf, buf2.buf);
+		} else {
+			strbuf_addf(&buf, "remote.%s.fetch", name);
+			if (track.nr == 0)
+				string_list_append(&track, "*");
+			for (size_t i = 0; i < track.nr; i++)
+				add_branch(buf.buf, track.items[i].string,
+					   name, mirror, &buf2);
 		}
 	}
 
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 5fbfcb0848..0168d5abfe 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -137,6 +137,22 @@ test_expect_success 'filters are listed by git remote -v only' '
 	test_grep ! "\[blob:none\]" out
 '
 
+test_expect_success '--limited-fetch works in a full repository too' '
+	test_when_finished "rm -rf full-add" &&
+	git clone --no-local one full-add &&
+	(
+		cd full-add &&
+		git remote add --limited-fetch upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.refmap &&
+		test_must_fail git config get remote.upstream.fetch
+	)
+'
+
+test_expect_success '--limited-fetch conflicts with -t' '
+	test_must_fail git remote add --limited-fetch -t main upstream ../two
+'
+
 test_expect_success 'check remote-tracking' '
 	(
 		cd test &&

Documentation/git-remote.adoc, builtin/remote.c, t/t5505-remote.sh

diff --git a/Documentation/git-remote.adoc b/Documentation/git-remote.adoc
index 4255f8b3e6..80f8a4a183 100644
--- a/Documentation/git-remote.adoc
+++ b/Documentation/git-remote.adoc
@@ -52,6 +52,11 @@ Add a remote named _<name>_ for the repository at
 _<URL>_.  The command `git fetch <name>` can then be used to create and
 update remote-tracking branches `<name>/<branch>`.
 +
+If the repository is already a shallow repository (see linkgit:git-clone[1]
+`--depth`) and neither `-t`, `--mirror` nor `--no-limited-fetch` is given,
+`--limited-fetch` is turned on by default, so that `git fetch <name>` does
+not need to negotiate history for every branch the remote has.
++
 With `-f` option, `git fetch <name>` is run immediately after
 the remote information is set up.
 +
@@ -74,7 +79,8 @@ With `--limited-fetch` option, instead of a `remote.<name>.fetch` refspec
 that tracks all branches, `remote.<name>.refmap` is set up so that a
 refspec-less `git fetch <name>` only fetches branches our local branches
 are built on. See the `--refmap` entry in linkgit:git-fetch[1] for
-details.
+details. `--no-limited-fetch` explicitly disables this, overriding the
+shallow-repository default described above.
 +
 With `-m <master>` option, a symbolic-ref `refs/remotes/<name>/HEAD` is set
 up to point at remote's _<master>_ branch. See also the set-head command.
diff --git a/builtin/remote.c b/builtin/remote.c
index f036dd5d6f..0cf1126976 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -16,6 +16,7 @@
 #include "rebase.h"
 #include "refs.h"
 #include "refspec.h"
+#include "shallow.h"
 #include "odb.h"
 #include "strvec.h"
 #include "commit-reach.h"
@@ -238,7 +239,9 @@ static int add(int argc, const char **argv, const char *prefix,
 
 	if (!mirror || mirror & MIRROR_FETCH) {
 		int use_limited_fetch = mirror == MIRROR_NONE && track.nr == 0 &&
-			limited_fetch == 1;
+			(limited_fetch == 1 ||
+			 (limited_fetch == -1 &&
+			  is_repository_shallow(the_repository)));
 
 		strbuf_reset(&buf);
 		if (use_limited_fetch) {
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 0168d5abfe..f3b5905e9e 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -137,6 +137,66 @@ test_expect_success 'filters are listed by git remote -v only' '
 	test_grep ! "\[blob:none\]" out
 '
 
+test_expect_success 'add remote -t keeps an explicit refspec in a shallow repository' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add -t main upstream ../two &&
+		test_cmp_config "+refs/heads/main:refs/remotes/upstream/main" \
+			remote.upstream.fetch
+	)
+'
+
+test_expect_success 'add remote keeps the wildcard refspec in a full repository' '
+	test_when_finished "rm -rf full-add" &&
+	git clone --no-local one full-add &&
+	(
+		cd full-add &&
+		git remote add upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.fetch
+	)
+'
+
+test_expect_success 'a remote added in a shallow repository defaults to --limited-fetch' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.refmap &&
+		test_must_fail git config get remote.upstream.fetch &&
+		git fetch upstream main &&
+		git branch --set-upstream-to=upstream/main &&
+		test_cmp_config upstream branch.main.remote &&
+		test_cmp_config refs/heads/main branch.main.merge &&
+		git fetch upstream &&
+		git for-each-ref --format="%(refname)" refs/remotes/upstream >actual &&
+		cat >expect <<-\EOF &&
+		refs/remotes/upstream/HEAD
+		refs/remotes/upstream/main
+		EOF
+		test_cmp expect actual
+	)
+'
+
+test_expect_success '--no-limited-fetch overrides the shallow-repository default' '
+	test_when_finished "rm -rf shallow-add" &&
+	git clone --no-local --depth=1 --branch main --single-branch \
+		one shallow-add &&
+	(
+		cd shallow-add &&
+		git remote add --no-limited-fetch upstream ../two &&
+		test_cmp_config "+refs/heads/*:refs/remotes/upstream/*" \
+			remote.upstream.fetch &&
+		test_must_fail git config get remote.upstream.refmap
+	)
+'
+
 test_expect_success '--limited-fetch works in a full repository too' '
 	test_when_finished "rm -rf full-add" &&
 	git clone --no-local one full-add &&

diff --git c/t/t5586-fetch-refmap.sh w/t/t5586-fetch-refmap.sh
index b81fc48cbe..30a8d79c16 100755
--- c/t/t5586-fetch-refmap.sh
+++ w/t/t5586-fetch-refmap.sh
@@ -22,6 +22,35 @@ test_expect_success 'setup' '
 	git checkout main
 '
 
+test_expect_success 'remote.<name>.refmap without tracking (baseline)' '
+	test_when_finished "rm -fr fetch-refmap-baseline" &&
+	git init fetch-refmap-baseline &&
+	(
+		cd fetch-refmap-baseline &&
+		git remote add origin ../ &&
+
+		# without fetch refspec, but with fetch refmap
+		git config --unset-all remote.origin.fetch &&
+		git config remote.origin.refmap "+refs/heads/*:refs/remotes/origin/*" &&
+
+		# nothing tracked, nothing fetched, no error
+		git fetch origin 2>error &&
+		test_grep ! "fatal: --refmap option is only meaningful" error &&
+		git for-each-ref --format="%(refname)" refs/remotes/ >actual &&
+		test_line_count = 0 actual &&
+
+		# nothing tracked, explicit ref on the command line
+		git fetch origin main &&
+		git for-each-ref --format="%(refname)" refs/remotes/ >actual &&
+		echo refs/remotes/origin/main >expect &&
+		test_cmp expect actual &&
+
+		# what should happen when we have both refmap and refspec?
+		git config remote.origin.fetch "+refs/heads/*:refs/remotes/origin/*" &&
+		git fetch origin
+	)
+'
+
 test_expect_success 'clone shallow and single-branch, then add a second remote' '
 	git clone --no-local --depth=1 --branch main --single-branch . client &&
 	(