Re: Round-tripping key definitions

[Stefan Monnier <monnier@iro.umontreal.ca>]

> -(define-key global-map "\t" 'indent-for-tab-command)
> +(define-key global-map [TAB] 'indent-for-tab-command)
> +(define-key global-map [?\C-i] nil)
> +(define-key global-map [tab] nil)
> +(define-key function-key-map [?\C-i] [TAB])
> +(define-key function-key-map [tab] [TAB])

Sadly, I think this will introduce a fair bit of trouble because code
which currently does

    (define-key map "\t" ...)

expects this binding to apply to both `tab` and tty's TAB key.

We could try and fix it by having `tab` first fallback to `?\t` and only
then to `TAB`, but that currently can't be done with `function-key-map`
because `function-key-map` is not applied to its output.

We could do it via ad-hoc code (like we currently have for the
`drag-mouse-1` fallback to `mouse-1`) or we could introduce a new keymap
like `function-key-map` but that's applied repeatedly until it doesn't
apply any more (or until a binding is found).

Or maybe we could do

    (define-key function-key-map [tab] #'some-new-tab-remap)

and then make sure `some-new-tab-remap` can get enough info to figure
out whether this `tab` should be remapped to `TAB` or to `?\C-i`.

I remember wanting such a repeatedly applied keymap a few times in the
past, and similarly getting enough info for a function to be able to
decide whether to do would be useful in other cases as well.


        Stefan