fetch: add --update-shallow to accept refs that update .git/shallow

The same steps are done as in when --update-shallow is not given. The
only difference is we now add all shallow commits in "ours" and
"theirs" to .git/shallow (aka "step 8").

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/fetch-options.txt

@@ -21,6 +21,12 @@
 If the source repository is shallow, fetch as much as possible so that
 the current repository has the same history as the source repository.
 
+--update-shallow::
+	By default when fetching from a shallow repository,
+	`git fetch` refuses refs that require updating
+	.git/shallow. This option updates .git/shallow and accept such
+	refs.
+
 ifndef::git-pull[]
 --dry-run::
 	Show what would be done, without making any changes.

builtin/fetch.c

@@ -36,7 +36,7 @@ static int prune = -1; /* unspecified */
 
 static int all, append, dry_run, force, keep, multiple, update_head_ok, verbosity;
 static int progress = -1, recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
-static int tags = TAGS_DEFAULT, unshallow;
+static int tags = TAGS_DEFAULT, unshallow, update_shallow;
 static const char *depth;
 static const char *upload_pack;
 static struct strbuf default_rla = STRBUF_INIT;
@@ -104,6 +104,8 @@ static struct option builtin_fetch_options[] = {
 	{ OPTION_STRING, 0, "recurse-submodules-default",
 		   &recurse_submodules_default, NULL,
 		   N_("default mode for recursion"), PARSE_OPT_HIDDEN },
+	OPT_BOOL(0, "update-shallow", &update_shallow,
+		 N_("accept refs that update .git/shallow")),
 	OPT_END()
 };
 
@@ -768,6 +770,8 @@ static struct transport *prepare_transport(struct remote *remote)
 		set_option(transport, TRANS_OPT_KEEP, "yes");
 	if (depth)
 		set_option(transport, TRANS_OPT_DEPTH, depth);
+	if (update_shallow)
+		set_option(transport, TRANS_OPT_UPDATE_SHALLOW, "yes");
 	return transport;
 }
 

fetch-pack.c

@@ -993,6 +993,33 @@ static void update_shallow(struct fetch_pack_args *args,
 		sha1_array_append(&ref, sought[i]->old_sha1);
 	si->ref = &ref;
 
+	if (args->update_shallow) {
+		/*
+		 * remote is also shallow, .git/shallow may be updated
+		 * so all refs can be accepted. Make sure we only add
+		 * shallow roots that are actually reachable from new
+		 * refs.
+		 */
+		struct sha1_array extra = SHA1_ARRAY_INIT;
+		unsigned char (*sha1)[20] = si->shallow->sha1;
+		assign_shallow_commits_to_refs(si, NULL, NULL);
+		if (!si->nr_ours && !si->nr_theirs) {
+			sha1_array_clear(&ref);
+			return;
+		}
+		for (i = 0; i < si->nr_ours; i++)
+			sha1_array_append(&extra, sha1[si->ours[i]]);
+		for (i = 0; i < si->nr_theirs; i++)
+			sha1_array_append(&extra, sha1[si->theirs[i]]);
+		setup_alternate_shallow(&shallow_lock,
+					&alternate_shallow_file,
+					&extra);
+		commit_lock_file(&shallow_lock);
+		sha1_array_clear(&extra);
+		sha1_array_clear(&ref);
+		return;
+	}
+
 	/*
 	 * remote is also shallow, check what ref is safe to update
 	 * without updating .git/shallow

fetch-pack.h

@@ -23,6 +23,7 @@ struct fetch_pack_args {
 	unsigned check_self_contained_and_connected:1;
 	unsigned self_contained_and_connected:1;
 	unsigned cloning:1;
+	unsigned update_shallow:1;
 };
 
 /*

t/t5537-fetch-shallow.sh

@@ -141,4 +141,36 @@ EOF
 	)
 '
 
+test_expect_success 'fetch --update-shallow' '
+	(
+	cd shallow &&
+	git checkout master &&
+	commit 7 &&
+	git tag -m foo heavy-tag HEAD^ &&
+	git tag light-tag HEAD^:tracked
+	) &&
+	(
+	cd notshallow &&
+	git fetch --update-shallow ../shallow/.git refs/heads/*:refs/remotes/shallow/* &&
+	git fsck &&
+	git for-each-ref --sort=refname --format="%(refname)" >actual.refs &&
+	cat <<EOF >expect.refs &&
+refs/remotes/shallow/master
+refs/remotes/shallow/no-shallow
+refs/tags/heavy-tag
+refs/tags/light-tag
+EOF
+	test_cmp expect.refs actual.refs &&
+	git log --format=%s shallow/master >actual &&
+	cat <<EOF >expect &&
+7
+6
+5
+4
+3
+EOF
+	test_cmp expect actual
+	)
+'
+
 test_done

transport.c

@@ -477,6 +477,9 @@ static int set_git_option(struct git_transport_options *opts,
 	} else if (!strcmp(name, TRANS_OPT_KEEP)) {
 		opts->keep = !!value;
 		return 0;
+	} else if (!strcmp(name, TRANS_OPT_UPDATE_SHALLOW)) {
+		opts->update_shallow = !!value;
+		return 0;
 	} else if (!strcmp(name, TRANS_OPT_DEPTH)) {
 		if (!value)
 			opts->depth = 0;
@@ -543,6 +546,7 @@ static int fetch_refs_via_pack(struct transport *transport,
 	args.check_self_contained_and_connected =
 		data->options.check_self_contained_and_connected;
 	args.cloning = transport->cloning;
+	args.update_shallow = data->options.update_shallow;
 
 	if (!data->got_remote_heads) {
 		connect_setup(transport, 0, 0);

transport.h

@@ -11,6 +11,7 @@ struct git_transport_options {
 	unsigned followtags : 1;
 	unsigned check_self_contained_and_connected : 1;
 	unsigned self_contained_and_connected : 1;
+	unsigned update_shallow : 1;
 	int depth;
 	const char *uploadpack;
 	const char *receivepack;
@@ -152,6 +153,9 @@ struct transport *transport_get(struct remote *, const char *);
 /* Aggressively fetch annotated tags if possible */
 #define TRANS_OPT_FOLLOWTAGS "followtags"
 
+/* Accept refs that may update .git/shallow without --depth */
+#define TRANS_OPT_UPDATE_SHALLOW "updateshallow"
+
 /**
  * Returns 0 if the option was used, non-zero otherwise. Prints a
  * message to stderr if the option is not used.