(Fdisplay_buffer): Move call to

Vsplit_window_preferred_function out of conditions that check
if window is eligible for vertical splitting.
When Vsplit_window_preferred_function is non-nil, call it and use
its non-nil return value as window.  Otherwise, continue doing
vertical splitting using Fsplit_window with arg horflag=nil.
(syms_of_window) <Vsplit_window_preferred_function>: Change the
default value from `split-window' to nil.

1 files changed, 27 insertions, 18 deletions

diff --git a/src/window.c b/src/window.c
index 8cf2a45e6f2..3b93a6fdc9f 100644
--- a/src/window.c
+++ b/src/window.c
@@ -3848,16 +3848,22 @@ displayed.  */)
       else
         window = Fget_largest_window (frames, Qt);
 
-      /* If the largest window is tall enough, full-width, and either eligible
-         for splitting or the only window, split it.  */
-      if (!NILP (window)
-          && ! FRAME_NO_SPLIT_P (XFRAME (XWINDOW (window)->frame))
-          && WINDOW_FULL_WIDTH_P (XWINDOW (window))
-               && (window_height (window) >= split_height_threshold
-                   || (NILP (XWINDOW (window)->parent)))
-          && (window_height (window)
-              >= (2 * window_min_size_2 (XWINDOW (window), 0))))
-        window = call1 (Vsplit_window_preferred_function, window);
+      if (!NILP (Vsplit_window_preferred_function))
+        tem = call1 (Vsplit_window_preferred_function, window);
+
+      if (!NILP (tem))
+        window = tem;
+      else
+        /* If the largest window is tall enough, full-width, and either eligible
+           for splitting or the only window, split it.  */
+        if (!NILP (window)
+            && ! FRAME_NO_SPLIT_P (XFRAME (XWINDOW (window)->frame))
+            && WINDOW_FULL_WIDTH_P (XWINDOW (window))
+            && (window_height (window) >= split_height_threshold
+                || (NILP (XWINDOW (window)->parent)))
+            && (window_height (window)
+                >= (2 * window_min_size_2 (XWINDOW (window), 0))))
+          window = Fsplit_window (window, Qnil, Qnil);
       else
         {
           Lisp_Object upper, other;
@@ -3867,12 +3873,12 @@ displayed.  */)
              splitting and selected or the only window, split it.  */
           if (!NILP (window)
               && ! FRAME_NO_SPLIT_P (XFRAME (XWINDOW (window)->frame))
-                   && ((EQ (window, selected_window)
-                        && window_height (window) >= split_height_threshold)
-                       || (NILP (XWINDOW (window)->parent)))
-                   && (window_height (window)
-                       >= (2 * window_min_size_2 (XWINDOW (window), 0))))
-            window = call1 (Vsplit_window_preferred_function, window);
+              && ((EQ (window, selected_window)
+                   && window_height (window) >= split_height_threshold)
+                  || (NILP (XWINDOW (window)->parent)))
+              && (window_height (window)
+                  >= (2 * window_min_size_2 (XWINDOW (window), 0))))
+            window = Fsplit_window (window, Qnil, Qnil);
           else
             window = Fget_lru_window (frames, Qnil);
           /* If Fget_lru_window returned nil, try other approaches.  */
@@ -7596,9 +7602,12 @@ If there is only one window, it is split regardless of this value.  */);
                doc: /* Function to use to split a window.
 This is used by `display-buffer' to allow the user to choose whether
 to split windows horizontally or vertically or some mix of the two.
+When this variable is nil, `display-buffer' splits windows vertically.
+Otherwise, `display-buffer' calls this function to split a window.
 It is called with a window as single argument and should split it in two
-and return the new window.  */);
-  Vsplit_window_preferred_function = intern ("split-window");
+and return the new window, or return an appropriate existing window
+if splitting is not eligible.  */);
+  Vsplit_window_preferred_function = Qnil;
 
   DEFVAR_INT ("window-min-height", &window_min_height,
               doc: /* *Delete any window less than this tall (including its mode line).