Try to save selections from being disowned during frame deletion

* lisp/cus-start.el (standard): Add
`x-auto-preserve-selections'.
* src/xselect.c (x_clear_frame_selections): Collect deleted
selections into a variable and preserve them.
* src/xterm.c (x_preserve_selections): New function.
(syms_of_xterm): New variable `x-auto-preserve-selections'.
* src/xterm.h: Update prototypes.

etc/NEWS

@@ -2448,6 +2448,15 @@ be kept aligned with the buffer contents when the user switches
 This minor mode makes Emacs deactivate the mark in all buffers when
 the primary selection is obtained by another program.
 
+---
+** On X, Emacs will try to preserve selection ownership when a frame is deleted.
+This means that if you make Emacs the owner of a selection, such as by
+selecting some text into the clipboard or primary selection, and then
+delete the current frame, you will still be able to insert the
+contents of that selection into other programs as long as another
+frame is open on the same display.  This behavior can be disabled by
+setting the variable 'x-auto-preserve-selections' to nil.
+
 +++
 ** New predicate 'char-uppercase-p'.
 This returns non-nil if its argument its an uppercase character.

lisp/cus-start.el

@@ -834,6 +834,7 @@ since it could result in memory overflow and make Emacs crash."
              (x-scroll-event-delta-factor mouse float "29.1")
              (x-gtk-use-native-input keyboard boolean "29.1")
              (x-dnd-disable-motif-drag dnd boolean "29.1")
+             (x-auto-preserve-selections x boolean "29.1")
 	     ;; xselect.c
 	     (x-select-enable-clipboard-manager killing boolean "24.1")
 	     ;; xsettings.c
@@ -874,6 +875,8 @@ since it could result in memory overflow and make Emacs crash."
                            (equal "x-scroll-event-delta-factor"
                                   (symbol-name symbol))
                            (equal "x-dnd-disable-motif-drag"
+                                  (symbol-name symbol))
+                           (equal "x-auto-preserve-selections"
                                   (symbol-name symbol)))
 		       (featurep 'x))
 		      ((string-match "\\`x-" (symbol-name symbol))

src/xselect.c

@@ -1091,20 +1091,23 @@ x_handle_selection_event (struct selection_input_event *event)
 void
 x_clear_frame_selections (struct frame *f)
 {
-  Lisp_Object frame;
-  Lisp_Object rest;
+  Lisp_Object frame, rest, lost;
   struct x_display_info *dpyinfo = FRAME_DISPLAY_INFO (f);
   struct terminal *t = dpyinfo->terminal;
 
   XSETFRAME (frame, f);
+  lost = Qnil;
 
   /* Delete elements from the beginning of Vselection_alist.  */
   while (CONSP (t->Vselection_alist)
 	 && EQ (frame, XCAR (XCDR (XCDR (XCDR (XCAR (t->Vselection_alist)))))))
     {
-      /* Run the `x-lost-selection-functions' abnormal hook.  */
-      CALLN (Frun_hook_with_args, Qx_lost_selection_functions,
-	     Fcar (Fcar (t->Vselection_alist)));
+      if (!x_auto_preserve_selections)
+	/* Run the `x-lost-selection-functions' abnormal hook.  */
+	CALLN (Frun_hook_with_args, Qx_lost_selection_functions,
+	       Fcar (Fcar (t->Vselection_alist)));
+      else
+	lost = Fcons (Fcar (t->Vselection_alist), lost);
 
       tset_selection_alist (t, XCDR (t->Vselection_alist));
     }
@@ -1114,11 +1117,18 @@ x_clear_frame_selections (struct frame *f)
     if (CONSP (XCDR (rest))
 	&& EQ (frame, XCAR (XCDR (XCDR (XCDR (XCAR (XCDR (rest))))))))
       {
-	CALLN (Frun_hook_with_args, Qx_lost_selection_functions,
-	       XCAR (XCAR (XCDR (rest))));
+	if (!x_auto_preserve_selections)
+	  CALLN (Frun_hook_with_args, Qx_lost_selection_functions,
+		 XCAR (XCAR (XCDR (rest))));
+	else
+	  lost = Fcons (XCAR (XCDR (rest)), lost);
+
 	XSETCDR (rest, XCDR (XCDR (rest)));
 	break;
       }
+
+  if (x_auto_preserve_selections)
+    x_preserve_selections (dpyinfo, lost);
 }
 
 /* True if any properties for DISPLAY and WINDOW

src/xterm.c

@@ -27951,6 +27951,62 @@ x_uncatch_errors_for_lisp (struct x_display_info *dpyinfo)
     x_stop_ignoring_errors (dpyinfo);
 }
 
+/* Preserve the selections in LOST in another frame on DPYINFO.  LOST
+   is a list of local selections that were lost, due to their frame
+   being deleted.  */
+
+void
+x_preserve_selections (struct x_display_info *dpyinfo, Lisp_Object lost)
+{
+  Lisp_Object tail, frame, new_owner, tem;
+  Time timestamp;
+  Window owner;
+
+  new_owner = Qnil;
+
+  FOR_EACH_FRAME (tail, frame)
+    {
+      if (FRAME_X_P (XFRAME (frame))
+	  && FRAME_DISPLAY_INFO (XFRAME (frame)) == dpyinfo)
+	{
+	  new_owner = frame;
+	  break;
+	}
+    }
+
+  tail = lost;
+
+  FOR_EACH_TAIL_SAFE (tail)
+    {
+      tem = XCAR (tail);
+
+      /* The selection is really lost (since we cannot find a new
+	 owner), so run the appropriate hooks.  */
+      if (NILP (new_owner))
+	CALLN (Frun_hook_with_args, Qx_lost_selection_functions,
+	       XCAR (tem));
+      else
+	{
+	  CONS_TO_INTEGER (XCAR (XCDR (XCDR (tem))), Time, timestamp);
+
+	  /* This shouldn't be able to signal any errors, despite the
+	     call to `x_check_errors' inside.  */
+	  x_own_selection (XCAR (tem), XCAR (XCDR (tem)),
+			   new_owner, XCAR (XCDR (XCDR (XCDR (XCDR (tem))))),
+			   timestamp);
+
+	  /* Now check if we still don't own that selection, which can
+	     happen if another program set itself as the owner.  */
+	  owner = XGetSelectionOwner (dpyinfo->display,
+				      symbol_to_x_atom (dpyinfo, XCAR (tem)));
+
+	  if (owner != FRAME_X_WINDOW (XFRAME (new_owner)))
+	    CALLN (Frun_hook_with_args, Qx_lost_selection_functions,
+		   XCAR (tem));
+	}
+    }
+}
+
 void
 syms_of_xterm (void)
 {
@@ -28265,4 +28321,11 @@ reply from the X server, and signal any errors that occurred while
 executing the protocol request.  Otherwise, errors will be silently
 ignored without waiting, which is generally faster.  */);
   x_fast_protocol_requests = false;
+
+  DEFVAR_BOOL ("x-auto-preserve-selections", x_auto_preserve_selections,
+    doc: /* Whether or not to transfer selection ownership when deleting a frame.
+When non-nil, deleting a frame that is currently the owner of a
+selection will cause its ownership to be transferred to another frame
+on the same display.  */);
+  x_auto_preserve_selections = true;
 }

src/xterm.h

@@ -1643,6 +1643,7 @@ extern void xic_set_statusarea (struct frame *);
 extern void xic_set_xfontset (struct frame *, const char *);
 extern bool x_defined_color (struct frame *, const char *, Emacs_Color *,
                              bool, bool);
+extern void x_preserve_selections (struct x_display_info *, Lisp_Object);
 #ifdef HAVE_X_I18N
 extern void free_frame_xic (struct frame *);
 # if defined HAVE_X_WINDOWS && defined USE_X_TOOLKIT