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.

3 files changed, 81 insertions, 7 deletions

diff --git a/src/xselect.c b/src/xselect.c
index 25a75aec917..baab2c5c18f 100644
--- a/src/xselect.c
+++ b/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
diff --git a/src/xterm.c b/src/xterm.c
index 2b83efb2288..f86e4708ec5 100644
--- a/src/xterm.c
+++ b/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;
 }
diff --git a/src/xterm.h b/src/xterm.h
index a1ddf13463c..9b91ee45569 100644
--- a/src/xterm.h
+++ b/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