bug#70622: [PATCH] New window parameter 'cursor-type'

[Eli Zaretskii]

> Date: Sun, 28 Apr 2024 08:27:53 +0200
> From:  Eshel Yaron via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> This patch makes it possible to set the cursor type in a specific window,
> without affecting other windows that may be showing the same buffer.

Thanks, I have a few comments and questions below.

> --- a/doc/lispref/windows.texi
> +++ b/doc/lispref/windows.texi
> @@ -6691,6 +6691,15 @@ Window Parameters
>  window and should be used, with due care, exclusively by those
>  applications.  It might be replaced by an improved solution in future
>  versions of Emacs.
> +
> +@item cursor-type
> +@vindex cursor-type@r{, a window parameter}
> +If this parameter is set to a cons cell, its @sc{car} specifies the
> +shape of the cursor in this window, using the same format as the
> +buffer-local variable @code{cursor-type}.  @xref{Cursor Parameters}.
> +Use this window parameter instead of the @code{cursor-type} variable or
> +frame parameter when a buffer is displayed in multiple windows and you
> +want to change the cursor for one window without affecting the others.
>  @end table

This doesn't say what happens when the buffer-local variable and the
window parameter don't agree.

Also, the "Cursor Parameters" node should mention this window-specific
parameter, with a cross-reference.

> +*** New window parameter 'cursor-type'.
> +If this parameter is set to a cons cell, its 'car' specifies the shape
> +of the window's cursor, using the same format as the buffer-local
> +variable 'cursor-type'.

Why only cons cells are supported?

> +  win_cursor = window_parameter (w, Qcursor_type);
> +  if (CONSP (win_cursor))
>      {
> -      cursor_type = FRAME_DESIRED_CURSOR (f);
> -      *width = FRAME_CURSOR_WIDTH (f);
> +      cursor_type = get_specified_cursor_type (XCAR (win_cursor), width);
>      }

Same question here.

And I have a question: is this supposed to work for non-selected
windows as well?  The documentation you added says nothing about that,
but I wonder what was the intent?  The reason I ask is that we have two
buffer-local variables, not one, for both selected and non-selected
windows, whereas your patch provides just one window parameter.  How
will it interact with the buffer-local variables in both cases?

Also, what about the cursor in mini-windows?

In addition, what is supposed to happen when this new window-parameter
is changed? is the cursor supposed to be redrawn in the new shape
immediately, i.e. do you expect redisplay to happen right away to
update the relevant window?  If so, I'm not sure the patch ensures
such an update.  In particular, non-selected windows are not
guaranteed to be updated by redisplay cycles, unless redisplay is
told, either directly or indirectly, about the need to do so.  To test
this, bind to a simple key, like F8, a command that changes the
window-parameter, and see if the change takes effect as soon as you
expect.