Handle buffer-local 'window-size-change-functions' specially (Bug#32637)

* src/window.c (run_window_size_change_functions): Run a
buffer-local value once per each frame and only if at least
one window showing the buffer on that frame has changed its
size.  (Bug#32637)
* doc/lispref/windows.texi (Window Hooks): Describe new
behavior of buffer-local 'window-size-change-functions'.

1 files changed, 43 insertions, 5 deletions

diff --git a/src/window.c b/src/window.c
index 04de9656809..b81469b9d69 100644
--- a/src/window.c
+++ b/src/window.c
@@ -3442,7 +3442,11 @@ run_window_size_change_functions (Lisp_Object frame)
 {
   struct frame *f = XFRAME (frame);
   struct window *r = XWINDOW (FRAME_ROOT_WINDOW (f));
-  Lisp_Object functions = Vwindow_size_change_functions;
+
+  if (NILP (Vrun_hooks)
+      || !(f->can_x_set_window_size)
+      || !(f->after_make_frame))
+    return;
 
   if (FRAME_WINDOW_CONFIGURATION_CHANGED (f)
       /* Here we implicitly exclude the possibility that the height of
@@ -3450,11 +3454,44 @@ run_window_size_change_functions (Lisp_Object frame)
          of FRAME's root window alone.  */
       || window_size_changed (r))
     {
-      while (CONSP (functions))
+      Lisp_Object globals = Fdefault_value (Qwindow_size_change_functions);
+      Lisp_Object windows = Fwindow_list (frame, Qlambda, Qnil);
+      /* The buffers for which the local hook was already run.  */
+      Lisp_Object buffers = Qnil;
+
+      for (; CONSP (windows); windows = XCDR (windows))
+        {
+          Lisp_Object window = XCAR (windows);
+          Lisp_Object buffer = Fwindow_buffer (window);
+
+          /* Run a buffer-local value only once for that buffer and
+             only if at least one window showing that buffer on FRAME
+             actually changed its size.  Note that the function is run
+             with FRAME as its argument and as such oblivious to the
+             window checked below.  */
+          if (window_size_changed (XWINDOW (window))
+              && !Fmemq (buffer, buffers)
+              && Flocal_variable_p (Qwindow_size_change_functions, buffer))
+            {
+              Lisp_Object locals
+                = Fbuffer_local_value (Qwindow_size_change_functions, buffer);
+
+              while (CONSP (locals))
+                {
+                  if (!EQ (XCAR (locals), Qt))
+                    safe_call1 (XCAR (locals), frame);
+                  locals = XCDR (locals);
+                }
+
+              buffers = Fcons (buffer, buffers);
+            }
+        }
+
+      while (CONSP (globals))
         {
-          if (!EQ (XCAR (functions), Qt))
-            safe_call1 (XCAR (functions), frame);
-          functions = XCDR (functions);
+          if (!EQ (XCAR (globals), Qt))
+            safe_call1 (XCAR (globals), frame);
+          globals = XCDR (globals);
         }
 
       window_set_before_size_change_sizes (r);
@@ -7556,6 +7593,7 @@ syms_of_window (void)
   Fput (Qscroll_down, Qscroll_command, Qt);
 
   DEFSYM (Qwindow_configuration_change_hook, "window-configuration-change-hook");
+  DEFSYM (Qwindow_size_change_functions, "window-size-change-functions");
   DEFSYM (Qwindowp, "windowp");
   DEFSYM (Qwindow_configuration_p, "window-configuration-p");
   DEFSYM (Qwindow_live_p, "window-live-p");