Merge branch 'jc/upload-pack-send-symref' into maint

One long-standing flaw in the pack transfer protocol used by "git
clone" was that there was no way to tell the other end which branch
"HEAD" points at, and the receiving end needed to guess.  A new
capability has been defined in the pack protocol to convey this
information so that cloning from a repository with more than one
branches pointing at the same commit where the HEAD is at now
reliably sets the initial branch in the resulting repository.

* jc/upload-pack-send-symref:
  t5570: Update for clone-progress-to-stderr branch
  t5570: Update for symref capability
  clone: test the new HEAD detection logic
  connect: annotate refs with their symref information in get_remote_head()
  connect.c: make parse_feature_value() static
  upload-pack: send non-HEAD symbolic refs
  upload-pack: send symbolic ref information as capability
  upload-pack.c: do not pass confusing cb_data to mark_our_ref()
  t5505: fix "set-head --auto with ambiguous HEAD" test

6 files changed, 124 insertions, 20 deletions

diff --git a/cache.h b/cache.h
index 88d373dfe7..415d883080 100644
--- a/cache.h
+++ b/cache.h
@@ -1107,7 +1107,6 @@ extern struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
 extern int server_supports(const char *feature);
 extern int parse_feature_request(const char *features, const char *feature);
 extern const char *server_feature_value(const char *feature, int *len_ret);
-extern const char *parse_feature_value(const char *feature_list, const char *feature, int *len_ret);
 
 extern struct packed_git *parse_pack_index(unsigned char *sha1, const char *idx_path);
 
diff --git a/connect.c b/connect.c
index a0783d4867..553a80c734 100644
--- a/connect.c
+++ b/connect.c
@@ -6,8 +6,10 @@
 #include "run-command.h"
 #include "remote.h"
 #include "url.h"
+#include "string-list.h"
 
 static char *server_capabilities;
+static const char *parse_feature_value(const char *, const char *, int *);
 
 static int check_ref(const char *name, int len, unsigned int flags)
 {
@@ -59,6 +61,61 @@ static void die_initial_contact(int got_at_least_one_head)
 		    "and the repository exists.");
 }
 
+static void parse_one_symref_info(struct string_list *symref, const char *val, int len)
+{
+	char *sym, *target;
+	struct string_list_item *item;
+
+	if (!len)
+		return; /* just "symref" */
+	/* e.g. "symref=HEAD:refs/heads/master" */
+	sym = xmalloc(len + 1);
+	memcpy(sym, val, len);
+	sym[len] = '\0';
+	target = strchr(sym, ':');
+	if (!target)
+		/* just "symref=something" */
+		goto reject;
+	*(target++) = '\0';
+	if (check_refname_format(sym, REFNAME_ALLOW_ONELEVEL) ||
+	    check_refname_format(target, REFNAME_ALLOW_ONELEVEL))
+		/* "symref=bogus:pair */
+		goto reject;
+	item = string_list_append(symref, sym);
+	item->util = target;
+	return;
+reject:
+	free(sym);
+	return;
+}
+
+static void annotate_refs_with_symref_info(struct ref *ref)
+{
+	struct string_list symref = STRING_LIST_INIT_DUP;
+	const char *feature_list = server_capabilities;
+
+	while (feature_list) {
+		int len;
+		const char *val;
+
+		val = parse_feature_value(feature_list, "symref", &len);
+		if (!val)
+			break;
+		parse_one_symref_info(&symref, val, len);
+		feature_list = val + 1;
+	}
+	sort_string_list(&symref);
+
+	for (; ref; ref = ref->next) {
+		struct string_list_item *item;
+		item = string_list_lookup(&symref, ref->name);
+		if (!item)
+			continue;
+		ref->symref = xstrdup((char *)item->util);
+	}
+	string_list_clear(&symref, 0);
+}
+
 /*
  * Read all the refs from the other end
  */
@@ -66,6 +123,7 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
 			      struct ref **list, unsigned int flags,
 			      struct extra_have_objects *extra_have)
 {
+	struct ref **orig_list = list;
 	int got_at_least_one_head = 0;
 
 	*list = NULL;
@@ -113,10 +171,13 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
 		list = &ref->next;
 		got_at_least_one_head = 1;
 	}
+
+	annotate_refs_with_symref_info(*orig_list);
+
 	return list;
 }
 
-const char *parse_feature_value(const char *feature_list, const char *feature, int *lenp)
+static const char *parse_feature_value(const char *feature_list, const char *feature, int *lenp)
 {
 	int len;
 
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 8f6e3922dc..ac79dd915d 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -160,9 +160,7 @@ cat >test/expect <<EOF
 * remote two
   Fetch URL: ../two
   Push  URL: ../three
-  HEAD branch (remote HEAD is ambiguous, may be one of the following):
-    another
-    master
+  HEAD branch: master
   Local refs configured for 'git push':
     ahead  forces to master  (fast-forwardable)
     master pushes to another (up to date)
@@ -262,16 +260,12 @@ test_expect_success 'set-head --auto' '
 	)
 '
 
-cat >test/expect <<\EOF
-error: Multiple remote HEAD branches. Please choose one explicitly with:
-  git remote set-head two another
-  git remote set-head two master
-EOF
-
-test_expect_success 'set-head --auto fails w/multiple HEADs' '
+test_expect_success 'set-head --auto has no problem w/multiple HEADs' '
 	(
 		cd test &&
-		test_must_fail git remote set-head --auto two >output 2>&1 &&
+		git fetch two "refs/heads/*:refs/remotes/two/*" &&
+		git remote set-head --auto two >output 2>&1 &&
+		echo "two/HEAD set to master" >expect &&
 		test_i18ncmp expect output
 	)
 '
diff --git a/t/t5570-git-daemon.sh b/t/t5570-git-daemon.sh
index 1309702ba4..e06146835c 100755
--- a/t/t5570-git-daemon.sh
+++ b/t/t5570-git-daemon.sh
@@ -37,7 +37,7 @@ test_expect_success 'fetch changes via git protocol' '
 	test_cmp file clone/file
 '
 
-test_expect_failure 'remote detects correct HEAD' '
+test_expect_success 'remote detects correct HEAD' '
 	git push public master:other &&
 	(cd clone &&
 	 git remote set-head -d origin &&
diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index b3b11e61c0..f8e5a9a4ae 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -285,4 +285,15 @@ test_expect_success NOT_MINGW,NOT_CYGWIN 'clone local path foo:bar' '
 	git clone "./foo:bar" foobar
 '
 
+test_expect_success 'clone from a repository with two identical branches' '
+
+	(
+		cd src &&
+		git checkout -b another master
+	) &&
+	git clone src target-11 &&
+	test "z$( cd target-11 && git symbolic-ref HEAD )" = zrefs/heads/another
+
+'
+
 test_done
diff --git a/upload-pack.c b/upload-pack.c
index 8327dc0b7c..fd96f3be11 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -688,6 +688,16 @@ static int mark_our_ref(const char *refname, const unsigned char *sha1, int flag
 	return 0;
 }
 
+static void format_symref_info(struct strbuf *buf, struct string_list *symref)
+{
+	struct string_list_item *item;
+
+	if (!symref->nr)
+		return;
+	for_each_string_list_item(item, symref)
+		strbuf_addf(buf, " symref=%s:%s", item->string, (char *)item->util);
+}
+
 static int send_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
 {
 	static const char *capabilities = "multi_ack thin-pack side-band"
@@ -696,35 +706,64 @@ static int send_ref(const char *refname, const unsigned char *sha1, int flag, vo
 	const char *refname_nons = strip_namespace(refname);
 	unsigned char peeled[20];
 
-	if (mark_our_ref(refname, sha1, flag, cb_data))
+	if (mark_our_ref(refname, sha1, flag, NULL))
 		return 0;
 
-	if (capabilities)
-		packet_write(1, "%s %s%c%s%s%s agent=%s\n",
+	if (capabilities) {
+		struct strbuf symref_info = STRBUF_INIT;
+
+		format_symref_info(&symref_info, cb_data);
+		packet_write(1, "%s %s%c%s%s%s%s agent=%s\n",
 			     sha1_to_hex(sha1), refname_nons,
 			     0, capabilities,
 			     allow_tip_sha1_in_want ? " allow-tip-sha1-in-want" : "",
 			     stateless_rpc ? " no-done" : "",
+			     symref_info.buf,
 			     git_user_agent_sanitized());
-	else
+		strbuf_release(&symref_info);
+	} else {
 		packet_write(1, "%s %s\n", sha1_to_hex(sha1), refname_nons);
+	}
 	capabilities = NULL;
 	if (!peel_ref(refname, peeled))
 		packet_write(1, "%s %s^{}\n", sha1_to_hex(peeled), refname_nons);
 	return 0;
 }
 
+static int find_symref(const char *refname, const unsigned char *sha1, int flag,
+		       void *cb_data)
+{
+	const char *symref_target;
+	struct string_list_item *item;
+	unsigned char unused[20];
+
+	if ((flag & REF_ISSYMREF) == 0)
+		return 0;
+	symref_target = resolve_ref_unsafe(refname, unused, 0, &flag);
+	if (!symref_target || (flag & REF_ISSYMREF) == 0)
+		die("'%s' is a symref but it is not?", refname);
+	item = string_list_append(cb_data, refname);
+	item->util = xstrdup(symref_target);
+	return 0;
+}
+
 static void upload_pack(void)
 {
+	struct string_list symref = STRING_LIST_INIT_DUP;
+
+	head_ref_namespaced(find_symref, &symref);
+	for_each_namespaced_ref(find_symref, &symref);
+
 	if (advertise_refs || !stateless_rpc) {
 		reset_timeout();
-		head_ref_namespaced(send_ref, NULL);
-		for_each_namespaced_ref(send_ref, NULL);
+		head_ref_namespaced(send_ref, &symref);
+		for_each_namespaced_ref(send_ref, &symref);
 		packet_flush(1);
 	} else {
 		head_ref_namespaced(mark_our_ref, NULL);
 		for_each_namespaced_ref(mark_our_ref, NULL);
 	}
+	string_list_clear(&symref, 1);
 	if (advertise_refs)
 		return;