don't fail renaming a file in a torrent just because it doesn't exist (and the destination directory doesn't exist)

include/libtorrent/file.hpp

@@ -131,6 +131,7 @@ namespace libtorrent
 	TORRENT_EXTRA_EXPORT void remove_all(std::string const& f
 		, error_code& ec);
 	TORRENT_EXTRA_EXPORT void remove(std::string const& f, error_code& ec);
+	TORRENT_EXTRA_EXPORT bool exists(std::string const& f, error_code& ec);
 	TORRENT_EXTRA_EXPORT bool exists(std::string const& f);
 	TORRENT_EXTRA_EXPORT boost::int64_t file_size(std::string const& f);
 	TORRENT_EXTRA_EXPORT bool is_directory(std::string const& f

include/libtorrent/torrent.hpp

@@ -993,7 +993,7 @@ namespace libtorrent
 		// renames the file with the given index to the new name
 		// the name may include a directory path
 		// returns false on failure
-		bool rename_file(int index, std::string const& name);
+		void rename_file(int index, std::string const& name);
 
 		// unless this returns true, new connections must wait
 		// with their initialization.

src/file.cpp

@@ -865,15 +865,20 @@ namespace libtorrent
 		return s.file_size;
 	}
 
-	bool exists(std::string const& f)
+	bool exists(std::string const& f, error_code& ec)
 	{
-		error_code ec;
 		file_status s;
 		stat_file(f, &s, ec);
 		if (ec) return false;
 		return true;
 	}
 
+	bool exists(std::string const& f)
+	{
+		error_code ec;
+		return exists(f, ec);
+	}
+
 	void remove(std::string const& inf, error_code& ec)
 	{
 		ec.clear();

src/storage.cpp

@@ -479,12 +479,33 @@ namespace libtorrent
 		return false;
 	}
 
-	void default_storage::rename_file(int index, std::string const& new_filename, storage_error& ec)
+	void default_storage::rename_file(int index, std::string const& new_filename
+		, storage_error& ec)
 	{
 		if (index < 0 || index >= files().num_files()) return;
 		std::string old_name = files().file_path(index, m_save_path);
 		m_pool.release(this, index);
 
+		// if the old file doesn't exist, just succeed and change the filename
+		// that will be created. This shortcut is important because the
+		// destination directory may not exist yet, which would cause a failure
+		// even though we're not moving a file (yet). It's better for it to
+		// fail later when we try to write to the file the first time, because
+		// the user then will have had a chance to make the destination directory
+		// valid.
+		if (!exists(old_name, ec.ec))
+		{
+			if (ec.ec == boost::system::errc::no_such_file_or_directory)
+			{
+				ec.ec.clear();
+				return;
+			}
+
+			ec.file = index;
+			ec.operation = storage_error::rename;
+			return;
+		}
+
 #if TORRENT_DEBUG_FILE_LEAKS
 		print_open_files("release files", m_files.name().c_str());
 #endif

src/torrent.cpp

@@ -8203,7 +8203,7 @@ namespace libtorrent
 		return m_save_path;
 	}
 
-	bool torrent::rename_file(int index, std::string const& name)
+	void torrent::rename_file(int index, std::string const& name)
 	{
 		INVARIANT_CHECK;
 
@@ -8211,12 +8211,19 @@ namespace libtorrent
 		TORRENT_ASSERT(index < m_torrent_file->num_files());
 
 		// stoage may be NULL during shutdown
-		if (!m_storage.get()) return false;
+		if (!m_storage.get())
+		{
+			if (alerts().should_post<file_rename_failed_alert>())
+				alerts().post_alert(file_rename_failed_alert(get_handle()
+					, index, error_code(errors::session_is_closing
+						, get_libtorrent_category())));
+			return;
+		}
 
 		inc_refcount("rename_file");
 		m_ses.disk_thread().async_rename_file(m_storage.get(), index, name
 			, boost::bind(&torrent::on_file_renamed, shared_from_this(), _1));
-		return true;
+		return;
 	}
 
 	void torrent::move_storage(std::string const& save_path, int flags)