The Emacs component that's responsible for expanding
~ in file names is
expand-file-name. Unfortunately, it's written in C, and deep inside its bowels is code that assumes that what comes after
~ is a user name. Fortunately, Emacs has a generic way of adding a wrapper around functions, so you can do what you want if you don't mind repeating some of the logic in the built-in function.
Here's some completely untested code that should get you going. Look up “Advising Emacs Lisp Functions” in the Emacs Lisp manual for more information; the basic idea is that
defadvice adds some code to run before the actual code of
expand-file-name. Please signal the mistakes I've inevitably made in comments (whether you know how to fix them or not).
(ad-define-subr-args 'expand-file-name '(name &optional default-directory))
'("foo" . "/home/Documents/foo"))
(defadvice expand-file-name (before expand-file-name-custom-tilde
"User-defined expansions for ~NAME in file names."
(if (string-match "\\`\\(\\(.*/\\)?~\\([^:/]+\\)\\)/" name)
(let ((replacement (assoc (match-string 2 name) expand-file-name )))
(setq name (replace-match replacement t t name 1)))))))
I'll leave parsing the shortcuts in
.zshrc to fill
expand-file-name-custom-tilde-alist (or whatever technique you choose to keep the aliases in synch) as an exercise.