Handle and document that `delete-frame' may call functions in `delete-frame-functions' twice.

* src/frame.c (syms_of_frame): Add warning to `delete-frame-functions' description.

* lisp/frame.el (terminal-handle-delete-frame): Check that the frame is alive.
* lisp/server.el (server-handle-delete-frame): Ditto.  Remove bogus comment.

git-archimport-id: lorentey@elte.hu--2004/emacs--multi-tty--0--patch-375

1 files changed, 8 insertions, 1 deletions

diff --git a/src/frame.c b/src/frame.c
index f32ad7a9363..8ebcbc90b15 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -4326,7 +4326,14 @@ when the mouse is over clickable text.  */);
   DEFVAR_LISP ("delete-frame-functions", &Vdelete_frame_functions,
                doc: /* Functions to be run before deleting a frame.
 The functions are run with one arg, the frame to be deleted.
-See `delete-frame'.  */);
+See `delete-frame'.
+
+Note that functions in this list may be called twice on the same
+frame.  In the second invocation, the frame is already deleted, and
+the function should do nothing.  (You can use `frame-live-p' to check
+for this.)  This wrinkle happens when an earlier function in
+`delete-frame-functions' (indirectly) calls delete-frame
+recursively.  */);
   Vdelete_frame_functions = Qnil;
 
   DEFVAR_KBOARD ("default-minibuffer-frame", Vdefault_minibuffer_frame,