bug#60101: 29.0.60; help-quick should use C-/ for undo

bug#60101: 29.0.60; help-quick should use C-/ for undo

[Philip Kaludercic]

The new help-quick command makes use of `where-is-internal' to find the
binding for a command ti displays.  This works fine if a command has
only one binding, but in the case of `undo', C-_ is the first one it
suggests, since

    (mapcar #'key-description (where-is-internal 'undo))
    ;; => ("C-_" "<undo>" "C-/" "<menu-bar> <edit> <undo>")

    (key-description (where-is-internal 'undo nil t))
    ;; => "C-_"

It appears this issue can be resolved by setting

    (setq where-is-preferred-modifier 'C)

    (mapcar #'key-description (where-is-internal 'undo))
    ;; => ("C-_" "<undo>" "C-/" "<menu-bar> <edit> <undo>")

    (key-description (where-is-internal 'undo nil t))
    ;; => "C-/"

But to be honest, I don't understand why, nor do I think the solution is
particularly robust.

I think some general mechanism to associate preferred binding with keys
would be nice to have.  What I wonder is if this is general enough of a
use-case to be added to where-is-internal, or should this be fixed
inside of help-quick?

The other issue is how does one determine what binding is preferable.  I
had previously generalised that C-/ is obviously preferable, but that
differs from layout to layout and depending on what keys Emacs can even
detect (I believe C-x u is often the only key that can be used in TUI
mode).

In GNU Emacs 29.0.60 (build 5, x86_64-pc-linux-gnu, GTK+ Version
 3.24.35, cairo version 1.16.0) of 2022-12-14 built on quetzal
Repository revision: 622838b957e240d700585050e9ddbd036e690513
Repository branch: emacs-29
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bug#60101: 29.0.60; help-quick should use C-/ for undo

[Juri Linkov]

> I think some general mechanism to associate preferred binding with keys
> would be nice to have.  What I wonder is if this is general enough of a
> use-case to be added to where-is-internal, or should this be fixed
> inside of help-quick?

In lisp/bindings.el its preferred binding is defined by this line:

  (put 'undo :advertised-binding [?\C-x ?u])

bug#60101: 29.0.60; help-quick should use C-/ for undo

[Philip Kaludercic]

Juri Linkov <juri@linkov.net> writes:

>> I think some general mechanism to associate preferred binding with keys
>> would be nice to have.  What I wonder is if this is general enough of a
>> use-case to be added to where-is-internal, or should this be fixed
>> inside of help-quick?
>
> In lisp/bindings.el its preferred binding is defined by this line:
>
>   (put 'undo :advertised-binding [?\C-x ?u])

That is good, but it only solves the problem by providing the means.
The other issue is figuring out how the advertised binding can
automatically be set to whatever is preferred on the current system.  Is
there a way to find out what keyboard layout is being used, or at least
what modifiers have to be pressed for a key to be input?

bug#60101: 29.0.60; help-quick should use C-/ for undo

[Juri Linkov]

> The new help-quick command makes use of `where-is-internal' to find the
> binding for a command ti displays.  This works fine if a command has
> only one binding, but in the case of `undo', C-_ is the first one it
> suggests

I tried to reproduce this problem, and typed 'C-h C-h' that showed:

  Other Help Commands

     C-e 	Extending Emacs with external packages
     p 	Search for Emacs packages (see also M-x list-packages)
     P 	Describe a specific Emacs package

     t 	Start the Emacs tutorial
     M-x help-quick-or-quit 	Display the quick help buffer.
     e 	Show recent messages (from echo area)
     l 	Show last 300 input keystrokes (lossage)
     . 	Show local help at point

I wonder if typing the suggested 'M-x help-quick-or-quit'
is really a quick way to get help?

Then I typed 'M-x help-quick-or-quit RET' but it doesn't exist
with "[No match]".

Then after 'C-h C-h' I tried to type 'q' (that means 'quick')
but it closed the Help window.

Finally, I opened the source code and found the command
'M-x cheat-sheet RET' that displayed the Help buffer.

But there is 'undo' displayed as bound to 'C-x u', not to other keys.

bug#60101: 29.0.60; help-quick should use C-/ for undo

[Juri Linkov]

>> In lisp/bindings.el its preferred binding is defined by this line:
>>
>>   (put 'undo :advertised-binding [?\C-x ?u])
>
> That is good, but it only solves the problem by providing the means.
> The other issue is figuring out how the advertised binding can
> automatically be set to whatever is preferred on the current system.  Is
> there a way to find out what keyboard layout is being used, or at least
> what modifiers have to be pressed for a key to be input?

If a key would be unbound on a tty, this could help to exclude it
from the preferred keybindings.  For example, if C-/ was unbound
depending on a tty type, then this would fall back to 'C-x u':

  (put 'undo :advertised-binding '([?\C-/] [?\C-x ?u]))

But otherwise, could you formulate a clear criteria for excluding
some keys from the set of preferred keys?  Do you know how to
query the current keyboard layout, or to find the preferred modifiers?

bug#60101: 29.0.60; help-quick should use C-/ for undo

[Philip Kaludercic]

Juri Linkov <juri@linkov.net> writes:

>> The new help-quick command makes use of `where-is-internal' to find the
>> binding for a command ti displays.  This works fine if a command has
>> only one binding, but in the case of `undo', C-_ is the first one it
>> suggests
>
> I tried to reproduce this problem, and typed 'C-h C-h' that showed:
>
>   Other Help Commands
>
>      C-e 	Extending Emacs with external packages
>      p 	Search for Emacs packages (see also M-x list-packages)
>      P 	Describe a specific Emacs package
>
>      t 	Start the Emacs tutorial
>      M-x help-quick-or-quit 	Display the quick help buffer.
>      e 	Show recent messages (from echo area)
>      l 	Show last 300 input keystrokes (lossage)
>      . 	Show local help at point
>
> I wonder if typing the suggested 'M-x help-quick-or-quit'
> is really a quick way to get help?

The intended way to display the buffer is C-h q.

> Then I typed 'M-x help-quick-or-quit RET' but it doesn't exist
> with "[No match]".
>
> Then after 'C-h C-h' I tried to type 'q' (that means 'quick')
> but it closed the Help window.
>
> Finally, I opened the source code and found the command
> 'M-x cheat-sheet RET' that displayed the Help buffer.
>
> But there is 'undo' displayed as bound to 'C-x u', not to other keys.

Hmm, interestingly this is also the case for me using emacs -Q, but I
don't recally customising anything to change this...

bug#60101: 29.0.60; help-quick should use C-/ for undo

[Philip Kaludercic]

Juri Linkov <juri@linkov.net> writes:

>>> In lisp/bindings.el its preferred binding is defined by this line:
>>>
>>>   (put 'undo :advertised-binding [?\C-x ?u])
>>
>> That is good, but it only solves the problem by providing the means.
>> The other issue is figuring out how the advertised binding can
>> automatically be set to whatever is preferred on the current system.  Is
>> there a way to find out what keyboard layout is being used, or at least
>> what modifiers have to be pressed for a key to be input?
>
> If a key would be unbound on a tty, this could help to exclude it
> from the preferred keybindings.  For example, if C-/ was unbound
> depending on a tty type, then this would fall back to 'C-x u':
>
>   (put 'undo :advertised-binding '([?\C-/] [?\C-x ?u]))
>
> But otherwise, could you formulate a clear criteria for excluding
> some keys from the set of preferred keys?  Do you know how to
> query the current keyboard layout, or to find the preferred modifiers?

No, I don't know.  What I had in mind was a sort of ordering to find the
key with the fewest modifiers, depending on the keyboard layout.