Arch Linux

Description:

As suggested in #57640 (but not implemented by da45692), the 'directory' should end in // which makes swap file names more unique (like undodir). Without it, there are issues like https://github.com/vim/vim/issues/2685.

:help 'directory' has this to say
- For Unix and Win32, if a directory ends in two path separators "//"
or "\\", the swap file name will be built from the complete path to
the file with all path separators substituted to percent '%' signs.
This will ensure file name uniqueness in the preserve directory.

I also dislike putting swap files in ~/.vim/swap because it clutters the ~/.vim directory. A potential problem arising from this would be that users inadvertently tracking the swap directory with version control, which has similar (or worse) security implications to CVE-2017-1000382 if they publicly host their vim config. I recommend something like ~/.cache/vim-swap.

Vim also has a builtin mkdir() function, which is probably better than using an external tool.

Additional info:
* package version: 8.0.1542-2