How to tell if a key binding will overwrite another

Question

I configure numerous additional key bindings, and sometimes I unintentionally overwrite others. Is there a way to determine if a key binding is taken before binding a key, and if so throw an error?

Answer 1

See function lookup-key. It will tell you whether a given key is defined in a given map, including in the global map, or even (with non-nil arg ACCEPT-DEFAULTS) whether it has a fallback (default) binding in the current context.

For example, if you want to see whether C-M-kp-+ is defined in the current mode's map:

(lookup-key (current-local-map) (kbd "<C-M-S-kp-add>"))

And if you want to see whether it has a global binding:

(lookup-key (current-global-map) (kbd "<C-M-S-kp-add>"))

And if you want to see if has a default behavior in the context of the current mode, even though it is not specifically defined:

(lookup-key (current-local-map) (kbd "<C-M-S-kp-add>") t)

See also: Key Lookup.