Re: Standard check before creating large num of frames

[Eli Zaretskii <eliz@gnu.org>]

> From: Tino Calancha <tino.calancha@gmail.com>
> Date: Thu, 15 Sep 2016 15:26:43 +0900 (JST)
> Cc: tino.calancha@gmail.com
> 
> several functions might create new frames.  In particular when
> `pop-up-frames' is non-nil, `display-buffer' creates a new frame.
> Creating a lot of new frames might be expensive.
> 
> Some functions may ask for user confirmation before creating an
> many frames.
> For instance, see `ibuffer-do-view-1': this function ask for confirmation
> before creating > 3 frames.
> IMO, it's good if each function creating a large number of frames
> do a similar check.
> We might add a new option, for instance 'max-number-of-frames'
> or 'frame-max-number':
> 
> (defcustom max-number-of-frames 3
>    "Maximum number of frames to create before asking user confirmation."
>      :version "25.2"
>      :type 'integer
>      :group 'convenience)

FWIW, I don't like nagging users like that.  It could be an optional
feature, off by default, I guess.  Did you really hear from someone
complaining about too many frames open without their consent?

A couple of minor comments:

> (defun frame-create-many-frames-p (nframes &optional prompt)
>    "Return non-nil if it's OK to create NFRAMES.
> If NFRAMES + current number of frames is > `max-number-of-frames',
> ask for user confirmation.
> An optional arg is the prompt to ask the user."
>    (let* ((tot (+ nframes (length (frame-list))))
>           (str (or prompt (format "Really create %s frames? " nframes)))
>           (res (or (<= tot max-number-of-frames)
>                    (y-or-n-p str))))
>      res))

First, the message text is confusing: when the user asked for creating
a single additional frame, we are asking them

  Really create 4 frames?

The user didn't ask for 4 frames, she only asked for one.  A better
text would be

  You already have 3 frames; really create another one?

In addition, I think you should also allow the user to tell Emacs
never ask this question again in the current session, not just yes/no
for this one frame.