remote: add "git remote add --limited-fetch"

A remote added the ordinary way tracks every branch it has, via a
wildcard remote.<name>.fetch refspec. That is wasteful for a remote
whose history is only worth following for the branches actually in
use locally, and it can make "git fetch" negotiate history for
branches nobody asked for.

Give "git remote add" a --limited-fetch option that sets up
remote.<name>.refmap instead of remote.<name>.fetch, so that
"git fetch <name>" only fetches the branches already tracked, as
described in the previous commit. It is rejected together with
-t/--track or --mirror, since those already say explicitly what to
fetch.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: HaraldNordgren

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.
 +

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);
 		}
 	}
 

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 &&