gh-151675: Add tkinter Text.sync() and Text.pendingsync() (GH-151677)

Wrap the Tk text widget "sync" and "pendingsync" subcommands, which
control and report the synchronization of the displayed view with the
underlying text when line heights have not yet been computed.

Author: serhiy-storchaka

Doc/library/tkinter.rst

@@ -5608,6 +5608,29 @@ Widget classes
 
       .. versionadded:: 3.3
 
+   .. method:: sync(command=None)
+
+      Control the synchronization of the displayed view with the underlying
+      text, which may lag behind when line heights have not yet been computed
+      (for example, for lines that have never been displayed).
+      If *command* is omitted, bring the line metrics up to date immediately by
+      forcing computation of any outdated line heights, and return once they
+      are current.
+      Otherwise schedule *command* to be called, with no arguments, exactly
+      once as soon as all line heights are up to date; if there are no pending
+      calculations, it is called immediately.
+
+      .. versionadded:: next
+
+   .. method:: pendingsync()
+
+      Return ``True`` if the line height calculations are not up to date, and
+      ``False`` otherwise.
+      The ``<<WidgetViewSync>>`` virtual event fires whenever this state
+      changes, with the *detail* field set to the new value.
+
+      .. versionadded:: next
+
    .. method:: yview_pickplace(*what)
 
       Adjust the view so that the location given by *what* is visible.

Doc/whatsnew/3.16.rst

@@ -152,6 +152,11 @@ tkinter
   is possible.
   (Contributed by Serhiy Storchaka in :gh:`151674`.)
 
+* Added new :class:`!tkinter.Text` methods :meth:`~tkinter.Text.sync` and
+  :meth:`~tkinter.Text.pendingsync` which control and report the
+  synchronization of the displayed view with the underlying text.
+  (Contributed by Serhiy Storchaka in :gh:`151675`.)
+
 xml
 ---
 

Lib/test/test_tkinter/test_text.py

@@ -26,6 +26,18 @@ def test_debug(self):
             text.debug(olddebug)
             self.assertEqual(text.debug(), olddebug)
 
+    def test_sync(self):
+        text = self.text
+        # sync() returns None and brings line metrics up to date.
+        self.assertIsNone(text.sync())
+        self.assertIs(text.pendingsync(), False)
+
+        # sync(command) schedules a one-shot callback.
+        events = []
+        text.sync(command=lambda: events.append('synced'))
+        text.update()
+        self.assertEqual(events, ['synced'])
+
     def test_index(self):
         text = self.text
         text.insert('1.0', 'Lorem ipsum\ndolor sit amet')

Lib/tkinter/__init__.py

@@ -4110,6 +4110,44 @@ def peer_names(self): # new in Tk 8.5
         the widget itself)."""
         return self.tk.splitlist(self.tk.call(self._w, 'peer', 'names'))
 
+    def pendingsync(self): # new in Tk 8.5
+        """Return whether the line heights calculations are not up-to-date.
+
+        Return True if the line heights calculations are not up-to-date,
+        and False otherwise.
+        """
+        return self.tk.getboolean(self.tk.call(self._w, 'pendingsync'))
+
+    def sync(self, command=None): # new in Tk 8.5
+        """Control the synchronization of the view of the text widget.
+
+        If command is not specified, immediately bring the line metrics
+        up-to-date by forcing computation of any outdated line heights.
+        The command returns immediately if there is no such outdated line.
+
+        If command is specified, schedule it to be executed (by the event
+        loop) exactly once as soon as all line heights are up-to-date.
+        If there are no pending line metrics calculations, command is
+        executed immediately.
+        """
+        if command is None:
+            self.tk.call(self._w, 'sync')
+        else:
+            def callit():
+                try:
+                    command()
+                finally:
+                    try:
+                        self.deletecommand(name)
+                    except TclError:
+                        pass
+            try:
+                callit.__name__ = command.__name__
+            except AttributeError:
+                callit.__name__ = type(command).__name__
+            name = self._register(callit)
+            self.tk.call(self._w, 'sync', '-command', name)
+
     def replace(self, index1, index2, chars, *args): # new in Tk 8.5
         """Replaces the range of characters between index1 and index2 with
         the given characters and tags specified by args.

Misc/NEWS.d/next/Library/2026-06-19-12-00-01.gh-issue-151675.acLD7L.rst

@@ -0,0 +1,3 @@
+Add the :meth:`~tkinter.Text.sync` and :meth:`~tkinter.Text.pendingsync`
+methods of :class:`!tkinter.Text`, wrapping the Tk ``sync`` and
+``pendingsync`` subcommands.