Fix `window-configuration-change-hook' and `window-size-change-functions'

(1) Run `window-configuration-change-hook' if and only if at least
one window was deleted or created or shows another buffer since
last redisplay.

(2) Run `window-size-change-functions' if and only if at least
one window changed its size since last redisplay (in a few cases
`window-size-change-functions' will also run when no window
changed its size).

(3) Provide two functions `window-pixel-height-before-size-change'
and `window-pixel-width-before-size-change' that allow to easily
detect which window changed size.

* src/frame.h (struct frame): New boolean member
window_configuration_changed.
(FRAME_WINDOW_SIZES_CHANGED): Remove macro.
(FRAME_WINDOW_CONFIGURATION_CHANGED): New macro.
* src/frame.c (adjust_frame_size): Don't run
`window-configuration-change-hook'.
* src/window.h (struct window): New fields
pixel_width_before_size_change and pixel_height_before_size_change.
(WINDOW_INTERNAL_P): New macro.
* src/window.c (Fwindow_pixel_width_before_size_change)
(Fwindow_pixel_height_before_size_change): New functions.
(Fdelete_other_windows_internal, Fwindow_resize_apply)
(resize_frame_windows, Fsplit_window_internal)
(Fdelete_window_internal, grow_mini_window)
(shrink_mini_window, Fresize_mini_window_internal): Don't call
FRAME_WINDOW_SIZES_CHANGED.
(window_size_changed, window_set_before_size_change_sizes)
(run_window_size_change_functions): New functions.
(make_window): Initialize pixel_width_before_size_change and
pixel_height_before_size_change.
(Fdelete_window_internal): Don't call
run_window_configuration_change_hook.
(struct saved_window): Add pixel_height_before_size_change and
pixel_width_before_size_change.
(Fset_window_configuration): Try to identify window configuration
changes correctly so run_window_configuration_change_hook and
run_window_size_change_functions run only if configuration and size
really changed.
(save_window_save): Set the pixel_height_before_size_change and
pixel_width_before_size_change fields.
(Vwindow_size_change_functions): Move here definiton from xdisp.c.
* src/xdisp.c (prepare_menu_bars, redisplay_internal): Call
run_window_size_change_functions.
(Vwindow_size_change_functions): Move definition to window.c.
* src/xfns.c (x_set_menu_bar_lines): Don't call
run_window_configuration_change_hook.
* doc/lispref/windows.texi (Window Sizes): Document new
functions `window-pixel-height-before-size-change' and
`window-pixel-width-before-size-change'.
(Window Configurations): Mention that this may trigger
execution of `window-size-change-functions' although no window
changed size.
(Window Hooks): Update descriptions of `window-size-change-functions'
and `window-configuration-change-hook'.

1 files changed, 42 insertions, 25 deletions

diff --git a/doc/lispref/windows.texi b/doc/lispref/windows.texi
index f61f08a7f24..f215eb727a5 100644
--- a/doc/lispref/windows.texi
+++ b/doc/lispref/windows.texi
@@ -545,6 +545,12 @@ its pixel height is the pixel height of the screen areas spanned by its
 children.
 @end defun
 
+@defun window-pixel-height-before-size-change &optional Lisp_Object &optional window
+This function returns the height of window @var{window} in pixels at the
+time @code{window-size-change-functions} was run for the last time on
+@var{window}'s frame (@pxref{Window Hooks}).
+@end defun
+
 @cindex window pixel width
 @cindex pixel width of a window
 @cindex total pixel width of a window
@@ -559,6 +565,12 @@ If @var{window} is an internal window, its pixel width is the width of
 the screen areas spanned by its children.
 @end defun
 
+@defun window-pixel-width-before-size-change &optional Lisp_Object &optional window
+This function returns the width of window @var{window} in pixels at the
+time @code{window-size-change-functions} was run for the last time on
+@var{window}'s frame (@pxref{Window Hooks}).
+@end defun
+
 @cindex full-width window
 @cindex full-height window
   The following functions can be used to determine whether a given
@@ -4087,11 +4099,11 @@ was created for.
 The argument @var{configuration} must be a value that was previously
 returned by @code{current-window-configuration}.  The configuration is
 restored in the frame from which @var{configuration} was made, whether
-that frame is selected or not.  This always counts as a window size
-change and triggers execution of the @code{window-size-change-functions}
-(@pxref{Window Hooks}), because @code{set-window-configuration} doesn't
-know how to tell whether the new configuration actually differs from the
-old one.
+that frame is selected or not.  In some rare cases this may trigger
+execution of the @code{window-size-change-functions} (@pxref{Window
+Hooks}) even if the size of windows did not change at all.  The
+@code{window-configuration-change-hook} functions will be called if and
+only if at least one window was added to or deleted from the frame.
 
 If the frame from which @var{configuration} was saved is dead, all this
 function does is restore the three variables @code{window-min-height},
@@ -4378,33 +4390,38 @@ work.
 @end defvar
 
 @defvar window-size-change-functions
-This variable holds a list of functions to be called if the size of
-any window changes for any reason.  The functions are called at the
-beginning of a redisplay cycle, and just once for each frame on which
-size changes have occurred.
-
-Each function receives the frame as its sole argument.  There is no
-direct way to find out which windows on that frame have changed size, or
-precisely how.  However, if a size-change function records, at each
-call, the existing windows and their sizes, it can also compare the
-present sizes and the previous sizes.
-
-Creating or deleting windows counts as a size change, and therefore
-causes these functions to be called.  Changing the frame size also
-counts, because it changes the sizes of the existing windows.
+This variable holds a list of functions to be called if the size of any
+window changes for any reason.  The functions are called once per
+redisplay, and once for each frame on which size changes have occurred.
+
+Each function receives the frame as its sole argument.  To find out
+whether a specific window has changed size, compare the return values of
+@code{window-pixel-width-before-size-change} and
+@code{window-pixel-width} respectively
+@code{window-pixel-height-before-size-change} and
+@code{window-pixel-height} for that window (@pxref{Window Sizes}).
+
+These function are usually only called when at least one window was
+added or has changed size since the last time this hook was run for the
+associated frame.  In some rare cases this hook also runs when a window
+that was added intermittently has been deleted afterwards.  In these
+cases none of the windows on the frame will appear to have changed its
+size.
 
 You may use @code{save-selected-window} in these functions
 (@pxref{Selecting Windows}).  However, do not use
 @code{save-window-excursion} (@pxref{Window Configurations}); exiting
-that macro counts as a size change, which would cause these functions
-to be called over and over.
+that macro counts as a size change, which would cause these functions to
+be called again.
 @end defvar
 
 @defvar window-configuration-change-hook
-A normal hook that is run every time you change the window configuration
-of an existing frame.  This includes splitting or deleting windows,
-changing the sizes of windows, or displaying a different buffer in a
-window.
+A normal hook that is run every time the window configuration of a frame
+changes.  Window configuration changes include splitting and deleting
+windows and the display of a different buffer in a window.  Resizing the
+frame or individual windows do not count as configuration changes.  Use
+@code{window-size-change-functions}, see above, when you want to track
+size changes that are not caused by the deletion or creation of windows.
 
 The buffer-local part of this hook is run once for each window on the
 affected frame, with the relevant window selected and its buffer