Re: Current mode command discovery

[Robert Pluim]

>>>>> On Tue, 16 Feb 2021 21:24:12 +0200, Eli Zaretskii <eliz@gnu.org> said:

    >> From: Lars Ingebrigtsen <larsi@gnus.org>
    >> Cc: contovob@tcd.ie,  emacs-devel@gnu.org
    >> Date: Tue, 16 Feb 2021 19:57:02 +0100
    >> 
    >> Eli Zaretskii <eliz@gnu.org> writes:
    >> 
    >> > In "Incompatible Editing Changes in Emacs 28.1"?
    >> 
    >> No, in "Editing Changes in Emacs 28.1"...  But that section is perhaps a
    >> better one?  Feel free to move it (and expand upon it) if you wish.

    Eli> I'd prefer to make the feature opt-in, see my other message.  Then
    Eli> NEWS entry won't need to be moved.

That entry says:

    ** New user option 'read-extended-command-predicate'.
    This option controls how 'M-x TAB' performs completions.  The default
    predicate excludes modes for which the command is not applicable.

Iʼm failing to parse that second sentence. After spelunking, I think
you mean something like:

"The default predicate includes commands applicable to the modes
(major and minor) active in the current buffer".

The spelunking I had to do:

C-h v read-extended-command-predicate, I get:

    read-extended-command-predicate is a variable defined in `simple.el'.
    Its value is `completion-default-include-p'

With no description of what completion-default-include-p does, so then
I have to do

C-h f completion-default-include-p

to get to:

    completion-default-include-p is a compiled Lisp function in
    `simple.el'.

    (completion-default-include-p SYMBOL BUFFER)

    Say whether SYMBOL should be offered as a completion.
    If there's a `completion-predicate' for SYMBOL, the result from
    calling that predicate is called.  If there isn't one, this
    predicate is true if the command SYMBOL is applicable to the
    major mode in BUFFER, or any of the active minor modes in
    BUFFER.

OK, thatʼs clear, but we check 'completion-predicate' as well? Thatʼs
not in NEWS.

Robert