Why did I get an error message: wrong-type-argument stringp user-init-file

Question

I have (set-register ?E '(file . user-init-file)), so that I can easily jump to my config file. Previously I used a string to specify the path to my init file, but I figured I'd tidy it up a bit.

However, it doesn't work, and emacs complains about (wrong-type-argument stringp user-init-file), giving the following stack trace with debug-on-error enabled.

Debugger entered--Lisp error: (wrong-type-argument stringp user-init-file)
  expand-file-name(user-init-file)
  find-file-noselect(user-init-file nil nil nil)
  find-file(user-init-file)
  ad-Orig-jump-to-register(69 nil)
  jump-to-register(69 nil)
  call-interactively(jump-to-register nil nil)

For reference, this happens if I load emacs with -Q, and then eval the set-register... and then attempt to jump to the register.

What's going on here? Things like (find-file user-init-file) don't throw this error.

Answer 1

In your code user-init-file is not evaluated (it is quoted), so expand-file-name gets a symbol (and not a string), and complains about that.

Try this:

(set-register ?E (cons 'file user-init-file))

PS: You can also use the backquote:

(set-register ?E `(file . ,user-init-file))

PPS: A side note: as far as I can tell this case is hard to debug by running emacs with -Q: user-init-file evaluates to nil under emacs -Q, so

(set-register ?E `(file . ,user-init-file))
(jump-to-register ?E)

fails for a different reason.