For the default compliance mode, (GMStudio compatibility), working_directory, program_directory, and temp_directory need to include the final slash at the end of the string they return. Nocturne on the GMC said that program_directory and temp_directory do not include that slash due to a bug in GMStudio, and that it should include the final slash like working directory does.
Long story short:
In GM 8.1 and below compliance mode - there should be no slash at the end for these 3 constants.
In GMStudio 1.x and above compliance mode - there should be a slash at the end for these 3 constants.
temp_directory also seems to not be fully implemented, because whenever I use it, even though LGM gives it syntax highlighting as if it were implemented, it throws and error saying the value of the constant is undefined.
There's also a new directory constant in GMStudio called "game_save_id" - this still needs to be implemented into ENIGMA - it's GMStudio's sandbox directory. game_save_id includes the final slash and in GM 8.1 and below compliance this constant shouldn't be declared. Only declare/implement it in GMStudio 1.x and above compliance.
This is actually not that big of a deal, just go ahead and add
/anyway. Ideally you should be using
/because those will work on Linux and Mac as well as Windows.
For example, I ran this just fine in command prompt:
C:\>cd C:///Users///Owner////Desktop C:\Users\Owner\Desktop> C:\>cd C:\\\Users////Owner\\/Desktop C:\Users\Owner\Desktop>
Just go ahead and add one anyway because even if it is there it won't break.