Structures can be saved in arbitrary directories

The bug

Apparently caused by the fix of MC-123064 structure names containing dots can now be used to select the current or parent directory.

How to reproduce

1. /setblock ~ ~ ~ structure_block[mode=save]{mode:"SAVE",name:"../test"}
   

2. Open the structure block GUI and click "SAVE"
   → The structure was not saved in the structures folder but instead in the parent directory

Possible solutions

The easiest solution might be using a replacement character which is not allowed as part of a resource location. It would probably be a good idea to provide this as a method of the resource location class returning it as a sanitized path.

If you are searching for other solutions you might want to look at the ones in MC-131152, which are however mainly designed for that specific bug.