Allow to change save path without moving any files

include/libtorrent/storage_defs.hpp

@@ -1,5 +1,6 @@
 /*
 
+Copyright (c) 2023, Vladimir Golovnev
 Copyright (c) 2006-2007, 2009, 2013-2014, 2016-2020, 2022, Arvid Norberg
 Copyright (c) 2016, 2021, Alden Torres
 All rights reserved.
@@ -110,7 +111,15 @@ namespace libtorrent {
 
 		// if any file exist in the target, take those files instead
 		// of the ones we may have in the source.
-		dont_replace
+		dont_replace,
+
+        // don't move any source files, just forget about them
+        // and begin checking files at new save path
+        reset_save_path,
+
+        // don't move any source files, just change save path
+        // and continue working without any checks
+        reset_save_path_unchecked
 	};
 
 #if TORRENT_ABI_VERSION == 1

src/storage_utils.cpp

@@ -1,5 +1,6 @@
 /*
 
+Copyright (c) 2023, Vladimir Golovnev
 Copyright (c) 2016-2022, Arvid Norberg
 Copyright (c) 2017-2018, Alden Torres
 Copyright (c) 2017-2018, Steven Siloti
@@ -199,6 +200,12 @@ namespace libtorrent { namespace aux {
 			}
 		}
 
+        if (flags == move_flags_t::reset_save_path)
+			return { status_t::need_full_check, new_save_path };
+
+        if (flags == move_flags_t::reset_save_path_unchecked)
+            return { status_t::no_error, new_save_path };
+
 		// indices of all files we ended up copying. These need to be deleted
 		// later
 		aux::vector<bool, file_index_t> copied_files(std::size_t(f.num_files()), false);