Re: master 927b885 1/3: Disable filtering of commands in M-x completion

[Juri Linkov <juri@linkov.net>]

> I think we should take one of the below actions:
>
> a) Add a key to show the unfiltered list of matches in `M-x'.
>    (We could use any key, but how about just using `M-x M-x' to show the
>    unfiltered list?  It would affect recursive minibuffers, but we could
>    just require a third `M-x' for that.)
>
> b) Add a new command, e.g. on `C-x x x', that always acts like the old
>    `M-x'.
>
> c) Both.

Also maybe a key to toggle filtering in the already active completion
(and a key to toggle sorting).

> I have never understood why Emacs suggests commands for execution in a
> context where they will obviously fail.  I think this is a glaring
> deficiency in our default UI -- you are proposed useless commands (that
> won't work there, will screw up your buffer, etc.).  No longer doing
> that is in my view a big step forward for Emacs usability.

I have no problem with unrelated commands displayed by M-x,
but for the new option I'd like also to suggest to filter out
commands having "r" in their interactive specs - they signal
an error when the region is not active, so no need to show them.
Also filter out commands with "*" in read-only buffers.

> From the discussions we've had so far, it is my understanding that some
> like to use it for searching for and discovering commands.  That is fine
> and valid, and reason for having an option to opt-out of this behavior.
> (I also think we should add a `describe-command' to try to better cover
> this use-case.)

`describe-command' is a very good idea for searching and discovering commands.

> Footnotes:
> [1] Some modes are prudent in saying:
>
>        (unless (derived-p 'foo-mode) (user-error "Nope"))
>
>      I think up until now this has often been the right and safe thing
>      to do, but it has unfortunately been severely underused.  Yet it
>      still has the deficiency that the command will show up in 'M-x`,
>      and it provides no fire-escape.

Isearch mode uses such idiom that when an internal command is called
when Isearch is not active, then it's activated before the command
is executed, with such a guard clause:

  (unless isearch-mode (isearch-mode t))