I vaguely remember zsh in Manjaro (by default) having a tab completion that automatically added the slashes.
Never set it up myself though.

But I really hate having to worry about quoting my file variables in scripts.
So much, that after a certain complexity, I just give up the script and make the thing in C++.

Oh, and if I make a script that doesn't handle file names properly (because it's not required in that specific use case), I make sure to delete it after use, to prevent mistaken use later, which would otherwise cause more headache than just having to rewrite a script.