Face-changing text properties and help-echo now work with xterm-mouse.

* src/dispnew.c (update_mouse_position): New function for mouse
movement logic in 'handle_one_term_event' that can be shared across
different mouse backends.
(display--update-for-mouse-movement): New lisp function, call it.
* lisp/xt-mouse.el (xterm-mouse--handle-mouse-movement): New function
that calls 'display--update-for-mouse-movement'.
(xterm-mouse-translate-1): Call it.
* src/term.c (handle_one_term_event): Inline logic from
'term_mouse_movement' and call 'update_mouse_position'.
(term_mouse_movement): Delete.

lisp/xt-mouse.el

@@ -77,6 +77,7 @@ https://invisible-island.net/xterm/ctlseqs/ctlseqs.html)."
               (copy-sequence event))
 	vec)
        (is-move
+        (xterm-mouse--handle-mouse-movement)
         (if track-mouse vec
           ;; Mouse movement events are currently supposed to be
           ;; suppressed.  Return no event.
@@ -106,8 +107,14 @@ https://invisible-island.net/xterm/ctlseqs/ctlseqs.html)."
 	      (if (null track-mouse)
 		  (vector drag)
 		(push drag unread-command-events)
+                (xterm-mouse--handle-mouse-movement)
 		(vector (list 'mouse-movement ev-data))))))))))))
 
+(defun xterm-mouse--handle-mouse-movement ()
+  "Handle mouse motion that was just generated for XTerm mouse."
+  (display--update-for-mouse-movement (terminal-parameter nil 'xterm-mouse-x)
+                                      (terminal-parameter nil 'xterm-mouse-y)))
+
 ;; These two variables have been converted to terminal parameters.
 ;;
 ;;(defvar xterm-mouse-x 0

src/dispextern.h

@@ -3606,6 +3606,7 @@ extern Lisp_Object marginal_area_string (struct window *, enum window_part,
 extern void redraw_frame (struct frame *);
 extern bool update_frame (struct frame *, bool, bool);
 extern void update_frame_with_menu (struct frame *, int, int);
+extern int update_mouse_position (struct frame *, int, int);
 extern void bitch_at_user (void);
 extern void adjust_frame_glyphs (struct frame *);
 void free_glyphs (struct frame *);

src/dispnew.c

@@ -3323,6 +3323,53 @@ update_frame_with_menu (struct frame *f, int row, int col)
   display_completed = !paused_p;
 }
 
+/* Update the mouse position for a frame F.  This handles both
+   updating the display for mouse-face propreties and updating the
+   help echo text.
+
+   Returns the number of events generated.  */
+int
+update_mouse_position (struct frame *f, int x, int y)
+{
+  previous_help_echo_string = help_echo_string;
+  help_echo_string = Qnil;
+
+  note_mouse_highlight (f, x, y);
+
+  /* If the contents of the global variable help_echo_string
+     has changed, generate a HELP_EVENT.  */
+  if (!NILP (help_echo_string)
+      || !NILP (previous_help_echo_string))
+    {
+      Lisp_Object frame;
+      XSETFRAME (frame, f);
+
+      gen_help_event (help_echo_string, frame, help_echo_window,
+                      help_echo_object, help_echo_pos);
+      return 1;
+    }
+
+  return 0;
+}
+
+DEFUN ("display--update-for-mouse-movement", Fdisplay__update_for_mouse_movement,
+       Sdisplay__update_for_mouse_movement, 2, 2, 0,
+       doc: /* Handle mouse movement detected by Lisp code.
+
+This function should be called when Lisp code detects the mouse has
+moved, even if `track-mouse' is nil.  This handles updates that do not
+rely on input events such as updating display for mouse-face
+properties or updating the help echo text.  */)
+  (Lisp_Object mouse_x, Lisp_Object mouse_y)
+{
+  CHECK_FIXNUM (mouse_x);
+  CHECK_FIXNUM (mouse_y);
+
+  update_mouse_position (SELECTED_FRAME (), XFIXNUM (mouse_x),
+                         XFIXNUM (mouse_y));
+  return Qnil;
+}
+
 
 /************************************************************************
 			 Window-based updates
@@ -6494,6 +6541,7 @@ syms_of_display (void)
 {
   defsubr (&Sredraw_frame);
   defsubr (&Sredraw_display);
+  defsubr (&Sdisplay__update_for_mouse_movement);
   defsubr (&Sframe_or_buffer_changed_p);
   defsubr (&Sopen_termscript);
   defsubr (&Sding);

src/term.c

@@ -2430,22 +2430,6 @@ tty_draw_row_with_mouse_face (struct window *w, struct glyph_row *row,
   cursor_to (f, save_y, save_x);
 }
 
-static bool
-term_mouse_movement (struct frame *frame, Gpm_Event *event)
-{
-  /* Has the mouse moved off the glyph it was on at the last sighting?  */
-  if (event->x != last_mouse_x || event->y != last_mouse_y)
-    {
-      frame->mouse_moved = 1;
-      note_mouse_highlight (frame, event->x, event->y);
-      /* Remember which glyph we're now on.  */
-      last_mouse_x = event->x;
-      last_mouse_y = event->y;
-      return 1;
-    }
-  return 0;
-}
-
 /* Return the current time, as a Time value.  Wrap around on overflow.  */
 static Time
 current_Time (void)
@@ -2562,30 +2546,22 @@ handle_one_term_event (struct tty_display_info *tty, Gpm_Event *event)
 
   if (event->type & (GPM_MOVE | GPM_DRAG))
     {
-      previous_help_echo_string = help_echo_string;
-      help_echo_string = Qnil;
-
       Gpm_DrawPointer (event->x, event->y, fileno (tty->output));
 
-      if (!term_mouse_movement (f, event))
-        help_echo_string = previous_help_echo_string;
+      /* Has the mouse moved off the glyph it was on at the last
+         sighting?  */
+      if (event->x != last_mouse_x || event->y != last_mouse_y)
+        {
+          /* FIXME: These three lines can not be moved into
+             update_mouse_position unless xterm-mouse gets updated to
+             generate mouse events via C code.  See
+             https://lists.gnu.org/archive/html/emacs-devel/2020-11/msg00163.html */
+          last_mouse_x = event->x;
+          last_mouse_y = event->y;
+          f->mouse_moved = 1;
 
-      /* If the contents of the global variable help_echo_string
-         has changed, generate a HELP_EVENT.  */
-      if (!NILP (help_echo_string)
-	  || !NILP (previous_help_echo_string))
-	{
-	  Lisp_Object frame;
-
-	  if (f)
-	    XSETFRAME (frame, f);
-	  else
-	    frame = Qnil;
-
-	  gen_help_event (help_echo_string, frame, help_echo_window,
-		          help_echo_object, help_echo_pos);
-	  count++;
-	}
+          count += update_mouse_position (f, event->x, event->y);
+        }
     }
   else
     {