display-buffer change

display-buffer change

[David Kågedal]

I have seen a change in Emacs 22.1 from Emacs 21 that broke my use of
dedicated windows.

The problem is that (display-buffer buf) will change the contents of
the current window, if the other window in the frame has a dedicated
buffer.  In Emacs 21, a new window would be opened instead.

To see the difference, do the following:

Split an emacs frame in two windows showing buffers A and B:

   +-------------+
   |             |
   |      A      |
   |             |
   +-------------+
   |             |
   |      B      |
   |             |
   +-------------+

While in the lower window, run

    (set-window-dedicated-p (selected-window) t)

Now, in the upper window, run

    (display-buffer "C")

In Emacs 21, this will be the result:

   +-------------+
   |      A      |
   +-------------+
   |      C      |
   +-------------+
   |             |
   |      B      |
   |             |
   +-------------+

In Emacs 22, this will be the result:

   +-------------+
   |             |
   |      C      |
   |             |
   +-------------+
   |             |
   |      B      |
   |             |
   +-------------+

I use a dedicated small window at the bottom of my frame that always
contains the *compilation* buffer, and the new behaviour in Emacs 22
seriously lower the usability of a lots of command, such as viewing
diffs or showing source from gdb etc.

I didn't find anything in NEWS that indicated that this was somehow
intentional.

-- 
David Kågedal

Re: display-buffer change

[martin rudalics]

 > I have seen a change in Emacs 22.1 from Emacs 21 that broke my use of
 > dedicated windows.
 >
 > The problem is that (display-buffer buf) will change the contents of
 > the current window, if the other window in the frame has a dedicated
 > buffer.  In Emacs 21, a new window would be opened instead.

[...]

 > I use a dedicated small window at the bottom of my frame that always
 > contains the *compilation* buffer, and the new behaviour in Emacs 22
 > seriously lower the usability of a lots of command, such as viewing
 > diffs or showing source from gdb etc.
 >
 > I didn't find anything in NEWS that indicated that this was somehow
 > intentional.
 >

Please ignore if this has been already resolved.  You should be able to
handle this by customizing `split-height-threshold' to a reasonable
value (say 10).  Confer the doc-string of `display-buffer':

   If a full-width window on a splittable frame is available to display
   the buffer, it may be split, subject to the value of the variable
   `split-height-threshold'.

I didn't trace what caused the behavior to change from Emacs 21 to Emacs
22.  The Emacs 22 behavior is consistent with respect to the doc-strings
of `split-height-threshold' and `display-buffer' though.

Re: display-buffer change

[martin rudalics]

 > I have seen a change in Emacs 22.1 from Emacs 21 that broke my use of
 > dedicated windows.
 >
 > The problem is that (display-buffer buf) will change the contents of
 > the current window, if the other window in the frame has a dedicated
 > buffer.  In Emacs 21, a new window would be opened instead.

[...]

 > I use a dedicated small window at the bottom of my frame that always
 > contains the *compilation* buffer, and the new behaviour in Emacs 22
 > seriously lower the usability of a lots of command, such as viewing
 > diffs or showing source from gdb etc.
 >
 > I didn't find anything in NEWS that indicated that this was somehow
 > intentional.
 >

Could you please tell us whether you were able to resolve this problem.

In an earlier mail I tried to explain the new behavior as follows:

 > You should be able to handle this by customizing
 > `split-height-threshold' to a reasonable value (say 10).  Confer the
 > doc-string of `display-buffer':
 >
 >   If a full-width window on a splittable frame is available to display
 >   the buffer, it may be split, subject to the value of the variable
 >   `split-height-threshold'.
 >
 > I didn't trace what caused the behavior to change from Emacs 21 to Emacs
 > 22.  The Emacs 22 behavior is consistent with respect to the doc-strings
 > of `split-height-threshold' and `display-buffer' though.

Please tell me whether that explanation is satisfactory.

Thanks in advance.