Re: M-g in dired

[Juri Linkov <juri@jurta.org>]

>     However, if this is not what the docstring meant, and leaving the logic
>     of the current return value is desirable, then maybe `lookup-key' needs
>     an additional argument defining another logic of its return value.
>
> Why?
>
>     Otherwise, almost all code in `lookup-key' should be duplicated in
>     `shadow_lookup'.
>
> Why?

To fix the bug, I think changes should be made in `shadow_lookup'.
Let's see how it currently works for the case when dired-mode-map
defines the "M-g" key, and the global-map defines "M-gn":

`shadow_lookup' iterates over two maps (dired and global) and calls
`Flookup_key' on them.  When `Flookup_key' returns 1 for the key
"M-gn" on the dired map, the loop in `shadow_lookup' skips it
and advances to the next iteration on the global map where it finds
the command `next-error' bound to "M-gn", and returns it.

This causes the current code to assume that "M-gn" in the global map
is not shadowed by "M-g" in the dired map.  It fails due to the value 1
returned by `Flookup_key', which is unsuitable to decide whether "M-g"
is bound in the dired map or not, and thus whether it shadows "M-gn"
in the global map or not.

To fix this, I intended to use the same code as `Flookup_key' uses
to process key sequences, but additionally to check whether a shorter
prefix key is bound or not.  This can be achieved either by adding
a new argument to `Flookup_key' to check if a key is bound and to
return the corresponding return value (and not to change its current
default semantics of the return value), or to duplicate most code of
`Flookup_key' in `shadow_lookup' to do this.

-- 
Juri Linkov
http://www.jurta.org/emacs/