clone: set refs/remotes/origin/HEAD when branch is specified

When a branch is specified to check out in clone, update the remote
tracking `HEAD` to point to it.  This mimics git's behavior, when
`git clone -b <name>` is used.

Author: ethomson

src/clone.c

@@ -162,16 +162,45 @@ static int update_head_to_default(git_repository *repo)
 	return error;
 }
 
+static int update_remote_head_byname(
+	git_repository *repo,
+	const char *remote_name,
+	const char *tracking_branch_name,
+	const char *reflog_message)
+{
+	git_buf tracking_head_name = GIT_BUF_INIT;
+	git_reference *remote_head = NULL;
+	int error;
+
+	if ((error = git_buf_printf(&tracking_head_name,
+		"%s%s/%s",
+		GIT_REFS_REMOTES_DIR,
+		remote_name,
+		GIT_HEAD_FILE)) < 0)
+		goto cleanup;
+
+	error = git_reference_symbolic_create(
+		&remote_head,
+		repo,
+		git_buf_cstr(&tracking_head_name),
+		tracking_branch_name,
+		true,
+		reflog_message);
+
+cleanup:
+	git_reference_free(remote_head);
+	git_buf_dispose(&tracking_head_name);
+	return error;
+}
+
 static int update_remote_head(
 	git_repository *repo,
 	git_remote *remote,
 	git_buf *target,
 	const char *reflog_message)
 {
 	git_refspec *refspec;
-	git_reference *remote_head = NULL;
-	git_buf remote_head_name = GIT_BUF_INIT;
-	git_buf remote_branch_name = GIT_BUF_INIT;
+	git_buf tracking_branch_name = GIT_BUF_INIT;
 	int error;
 
 	/* Determine the remote tracking ref name from the local branch */
@@ -184,30 +213,19 @@ static int update_remote_head(
 	}
 
 	if ((error = git_refspec_transform(
-		&remote_branch_name,
+		&tracking_branch_name,
 		refspec,
 		git_buf_cstr(target))) < 0)
 		goto cleanup;
 
-	if ((error = git_buf_printf(&remote_head_name,
-		"%s%s/%s",
-		GIT_REFS_REMOTES_DIR,
-		git_remote_name(remote),
-		GIT_HEAD_FILE)) < 0)
-		goto cleanup;
-
-	error = git_reference_symbolic_create(
-		&remote_head,
+	error = update_remote_head_byname(
 		repo,
-		git_buf_cstr(&remote_head_name),
-		git_buf_cstr(&remote_branch_name),
-		true,
+		git_remote_name(remote),
+		git_buf_cstr(&tracking_branch_name),
 		reflog_message);
 
 cleanup:
-	git_reference_free(remote_head);
-	git_buf_dispose(&remote_branch_name);
-	git_buf_dispose(&remote_head_name);
+	git_buf_dispose(&tracking_branch_name);
 	return error;
 }
 
@@ -277,8 +295,11 @@ static int update_head_to_branch(
 	if ((retcode = git_reference_lookup(&remote_ref, repo, git_buf_cstr(&remote_branch_name))) < 0)
 		goto cleanup;
 
-	retcode = update_head_to_new_branch(repo, git_reference_target(remote_ref), branch,
-			reflog_message);
+	if ((retcode = update_head_to_new_branch(repo, git_reference_target(remote_ref), branch,
+			reflog_message)) < 0)
+		goto cleanup;
+
+	retcode = update_remote_head_byname(repo, remote_name, remote_branch_name.ptr, reflog_message);
 
 cleanup:
 	git_reference_free(remote_ref);

tests/clone/nonetwork.c

@@ -158,6 +158,8 @@ void test_clone_nonetwork__can_prevent_the_checkout_of_a_standard_repo(void)
 
 void test_clone_nonetwork__can_checkout_given_branch(void)
 {
+	git_reference *remote_head;
+
 	g_options.checkout_branch = "test";
 	cl_git_pass(git_clone(&g_repo, cl_git_fixture_url("testrepo.git"), "./foo", &g_options));
 
@@ -167,6 +169,12 @@ void test_clone_nonetwork__can_checkout_given_branch(void)
 	cl_assert_equal_s(git_reference_name(g_ref), "refs/heads/test");
 
 	cl_assert(git_path_exists("foo/readme.txt"));
+
+	cl_git_pass(git_reference_lookup(&remote_head, g_repo, "refs/remotes/origin/HEAD"));
+	cl_assert_equal_i(GIT_REFERENCE_SYMBOLIC, git_reference_type(remote_head));
+	cl_assert_equal_s("refs/remotes/origin/test", git_reference_symbolic_target(remote_head));
+
+	git_reference_free(remote_head);
 }
 
 static int clone_cancel_fetch_transfer_progress_cb(