Re: master 12409c9: New transient mode 'repeat-mode' to allow shorter key sequences (bug#46515)

[Juri Linkov]

>> +(defvar next-error-repeat-map
>> +  (let ((map (make-sparse-keymap)))
>> +    (define-key map    "n" 'next-error)
>> +    (define-key map "\M-n" 'next-error)
>> +    (define-key map    "p" 'previous-error)
>> +    (define-key map "\M-p" 'previous-error)
>> +    map)
>> +  "Keymap to repeat next-error key sequences.  Used in `repeat-mode'.")
>> +(put 'next-error 'repeat-map 'next-error-repeat-map)
>> +(put 'previous-error 'repeat-map 'next-error-repeat-map)
>
> Could we avoid this duplication between the map and the
> `repeat-map` property?
>
>> +            (set-transient-map map)))))))
>
> For example passing a second argument t to `set-transient-map` makes
> `set-transient-map` look to see if the key just typed was found in the
> map and if so keep the transient alive, which seems to [after an
> admittedly cursory check of the code] play the same role as what your
> `repeat-map` property does, but without the duplication.

The current design relies on post-command-hook that runs after every command.
Using the second argument KEEP-PRED of set-transient-map will add duplication:
the same map will be set by both post-command-hook and KEEP-PRED.

So currently there is no duplication.  But is it possible to avoid duplication
when using KEEP-PRED too?  Could post-command-hook detect that KEEP-PRED
is in use for the next command, and not to call set-transient-map again?