Re: emacs-25 3722a69: Fix bugs in window resizing code

[martin rudalics]

>>      (shrink-window, enlarge-window): Fix bug#22723 where windows
>>      with preserved size would not get resized.  Also now signal an
>>      error when the window cannot be shrunk or enlarged as requested.
>
> [snip]
>
>> +      (error "Cannot shrink selected window")))))
>
> I was surprised to see my code failing because of this change. Throwing
> an error on a case where previously nothing was done amounts to an API
> change. My code was fixed by wrapping the call to enlarge-window with
> ignore-errors, but I'm worried about all the code out there.

Sorry, but this fix was motivated by the following explanation in the
Emacs manual:

      The command `C-x ^' (`enlarge-window') makes the selected window one
   line taller, taking space from a vertically adjacent window without
   changing the height of the frame.  With a positive numeric argument,
   this command increases the window height by that many lines; with a
   negative argument, it reduces the height by that many lines.  If there
   are no vertically adjacent windows (i.e., the window is at the full
   frame height), that signals an error.  The command also signals an
   error if you attempt to reduce the height of any window below a certain
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   minimum number of lines, specified by the variable `window-min-height'
   (the default is 4).

      Similarly, `C-x }' (`enlarge-window-horizontally') makes the
   selected window wider, and `C-x {' (`shrink-window-horizontally') makes
   it narrower.  These commands signal an error if you attempt to reduce
                                                       ^^^^^^^^^^^^^^^^^
   the width of any window below a certain minimum number of columns,
   ^^^^^^^^^^^^^^^^^^^^^^^
   specified by the variable `window-min-width' (the default is 10).

We can easily change that to not signal an error but then behaviors like
the one reported by Eli will get passed by unnoticed.  Emacsen < 23
silently could delete windows when you made them too small with these
commands.  This was deprecated but IIRC no one ever expressed a
preference as to how these functions _should_ behave when there is not
enough space.  Suggestions welcome.

Personally, I'd never use ‘enlarge-window’ and ‘shrink-window’ in Lisp
code.  IMO these are for interactive use only (supported by the fact
that neither of these functions is documented in the Elisp manual).

martin