reopen 60815
thanks

>> Then I guess this report can be closed, done.
>
> I think so. Your patch would allow me to just change the value of
> dired-isearch-filenames-toggle-key, instead of monkey-patching the
> whole function in my .emacs.
>
> But it seems that some key-bindings are much harder to change than
> another. "M-s", is such an example, because many modes decide to
> override it in their keymaps. Just an idea: Wouldn't it be nice, if
> there were an configuration that defines what is the key sequence for
> "the M-s search" (M-s by default), and if major modes want to override
> the "M-s search commands", they would respect what the configuration
> says.

Indeed, there is already such variable: `search-map'.  So you can do:

  (define-key global-map [f6] search-map)

> For example, If I rebind "M-s" to say "M-6", then the
> dired-isearch-filenames-setup function would define the "M-6ff"
> binding, instead of "M-sff". I am not sure if this is a good idea, but
> this seems like a good approach to me.
>
> So basically, I propose, instead of the
> "dired-isearch-filenames-toggle-key" configuration ("M-sfff by
> default), to have, say "global-search-key-sequence" ("M-s" by
> default), which all major modes can use when building their local
> keymaps. This way, I would not need to fix this binding in every major
> mode which overrides it, wrongly believing that M-s is my "search
> prefix".

The problem is that isearch doesn't use the global "M-s" keymap,
but hard-codes "M-s" used in isearch-map.  The patch below adds
a new variable for the isearch's keymap "M-s" that you can
customize with e.g.:

  (define-key isearch-mode-map [f6] isearch-mode-search-map)

Needless to say this patch is for master.