Binding a key sequence to a key sequence instead of a command

Question

In my .emacs, I tried to use

(global-set-key (kbd "M-r") (kbd "C-x r j")

so I can use M-r to jump to a register. However, doing this and using the command gives

After 0 kbd macro iterations: Args out of range: [], 0

as an error in the minibuffer. Looking up the shortcut with C-h k shows that the keyboard shortcut is bound to jump-to-register. Then, using

(global-set-key (kbd "M-r") 'jump-to-register)

gets the desired behavior, and my shortcut works.

My question is: why doesn't my first attempt work, esp. if it just really seems to be calling the same function?

Answer 1

I can reproduce this in Emacs 25.2.2. The problem is that when jump-to-register attempts to read the character that identifies the register, Emacs still thinks it's running a macro, but it has no more characters available. Your approach would work with a function that doesn't attempt to read extra input.

At the Lisp level, jump-to-register calls read-key which calls read-key-sequence-vector. In this scenario, read-key-sequence-vector returns an empty vector. read-key does not expect this and throws the error you saw. This looks like a bug in read-key-sequence-vector since it isn't documented as ever reading an empty vector and I don't see why it would.