implemented window-start

rust_src/src/lib.rs

@@ -222,6 +222,7 @@ pub extern "C" fn rust_init_syms() {
         defsubr(&*windows::Sselected_window);
         defsubr(&*windows::Swindow_buffer);
         defsubr(&*windows::Swindow_valid_p);
+        defsubr(&*windows::Swindow_start);
         defsubr(&*process::Sget_process);
         defsubr(&*process::Sprocessp);
         defsubr(&*lists::Satom);

rust_src/src/windows.rs

@@ -25,6 +25,11 @@ impl LispWindowRef {
     pub fn contents(self) -> LispObject {
         LispObject::from_raw(self.contents)
     }
+
+    #[inline]
+    pub fn start_marker(self) -> LispObject {
+        LispObject::from_raw(self.start)
+    }
 }
 
 /// Return t if OBJECT is a window and nil otherwise.
@@ -98,3 +103,16 @@ pub fn window_valid_p(object: LispObject) -> LispObject {
         |win| win.contents().is_not_nil(),
     ))
 }
+
+/// Return position at which display currently starts in WINDOW.
+/// WINDOW must be a live window and defaults to the selected one.
+/// This is updated by redisplay or by calling `set-window-start'.
+#[lisp_fn(min = "0")]
+pub fn window_start(window: LispObject) -> LispObject {
+    let win = if window.is_nil() {
+        selected_window()
+    } else {
+        window
+    };
+    marker_position(win.as_live_window_or_error().start_marker())
+}

src/window.c

@@ -1506,15 +1506,6 @@ WINDOW must be a live window and defaults to the selected one.  */)
   return Fmarker_position (decode_live_window (window)->old_pointm);
 }
 
-DEFUN ("window-start", Fwindow_start, Swindow_start, 0, 1, 0,
-       doc: /* Return position at which display currently starts in WINDOW.
-WINDOW must be a live window and defaults to the selected one.
-This is updated by redisplay or by calling `set-window-start'.  */)
-  (Lisp_Object window)
-{
-  return Fmarker_position (decode_live_window (window)->start);
-}
-
 /* This is text temporarily removed from the doc string below.
 
 This function returns nil if the position is not currently known.
@@ -7720,7 +7711,6 @@ displayed after a scrolling operation to be somewhat inaccurate.  */);
   defsubr (&Scoordinates_in_window_p);
   defsubr (&Swindow_at);
   defsubr (&Swindow_old_point);
-  defsubr (&Swindow_start);
   defsubr (&Swindow_end);
   defsubr (&Sset_window_point);
   defsubr (&Sset_window_start);