New focus management interface

focus-in-hook and focus-out-hook don't accurately reflect actual
user-visible focus states.  Add a new focus interface and mark the old
one obsolete.

* doc/lispref/frames.texi (Input Focus): Document new focus
functions.  Remove references to the now-obsolete focus hooks.

* lisp/frame.el (frame-focus-state): New function.
(after-focus-change-function): New variable.
(focus-in-hook, focus-out-hook): Move to lisp from C;
mark obsolete.

* lisp/term/xterm.el (xterm-translate-focus-in)
(xterm-translate-focus-out): Track tty focus in `tty-focus-state'
terminal parameter; call `after-focus-change-function'.
(xterm--suspend-tty-function): New function.

* src/frame.c (Fhandle_switch_frame): Update docstring; don't call
focus hooks.
(focus-in-hook, focus-out-hook): Remove: moved to lisp.
(syms_of_frame): Remove unread_switch_frame; add
Vunread_switch_frame.

* src/keyboard.c:
(Finternal_handle_focus_in): New function.
(make_lispy_event): Always report focus events to lisp; don't
translate them to switch events sometimes.  Lisp can take care of
creating synthetic switch-frame events via
`internal-handle-focus-in'.

* src/w32term.c (x_focus_changed): Remove switch-avoidance logic:
just directly report focus changes to lisp.

* src/xterm.c (x_focus_changed): Remove switch-avoidance logic:
just directly report focus changes to lisp.

1 files changed, 9 insertions, 2 deletions

diff --git a/lisp/term/xterm.el b/lisp/term/xterm.el
index b3b7a216352..ce4e18efff8 100644
--- a/lisp/term/xterm.el
+++ b/lisp/term/xterm.el
@@ -115,13 +115,20 @@ Return the pasted text as a string."
 ;; notifications) instead of read-event (which can't).
 
 (defun xterm-translate-focus-in (_prompt)
-  (handle-focus-in)
+  (setf (terminal-parameter nil 'tty-focus-state) 'focused)
+  (funcall after-focus-change-function)
   [])
 
 (defun xterm-translate-focus-out (_prompt)
-  (handle-focus-out)
+  (setf (terminal-parameter nil 'tty-focus-state) 'defocused)
+  (funcall after-focus-change-function)
   [])
 
+(defun xterm--suspend-tty-function (_tty)
+  ;; We can't know what happens to the tty after we're suspended
+  (setf (terminal-parameter nil 'tty-focus-state) nil)
+  (funcall after-focus-change-function))
+
 ;; Similarly, we want to transparently slurp the entirety of a
 ;; bracketed paste and encapsulate it into a single event.  We used to
 ;; just slurp up the bracketed paste content in the event handler, but