gh-112938: IDLE - Fix uninteruptable hang when Shell gets rapid continuous output. (#124310)

https://github.com/python/cpython/issues/88496 replaced text.update with text.update_idletasks in colorizer.py and outwin.py to fix test failures on macOS.  While theoretically correct, the result was Shell freezing when receiving continuous short strings to print.  Test: `while 1: 1`.

The guess is that there is no idle time in which to do the screen update.  Reverting the change in one of the files,
outwin, fixes the issue.  Colorizer runs ever 1/20 second and seems to work fine.

When running test-outwin on macOS, alias 'update'
to 'update_idletasks on the text used for testing.

Lib/idlelib/idle_test/test_outwin.py

@@ -1,6 +1,7 @@
 "Test outwin, coverage 76%."
 
 from idlelib import outwin
+import sys
 import unittest
 from test.support import requires
 from tkinter import Tk, Text
@@ -18,6 +19,10 @@ class OutputWindowTest(unittest.TestCase):
         root.withdraw()
         w = cls.window = outwin.OutputWindow(None, None, None, root)
         cls.text = w.text = Text(root)
+        if sys.platform == 'darwin':  # Issue 112938
+            cls.text.update = cls.text.update_idletasks
+            # Without this, test write, writelines, and goto... fail.
+            # The reasons and why macOS-specific are unclear.
 
     @classmethod
     def tearDownClass(cls):

Lib/idlelib/outwin.py

@@ -112,7 +112,7 @@ class OutputWindow(EditorWindow):
         assert isinstance(s, str)
         self.text.insert(mark, s, tags)
         self.text.see(mark)
-        self.text.update_idletasks()
+        self.text.update()
         return len(s)
 
     def writelines(self, lines):

Misc/NEWS.d/next/IDLE/2024-09-21-23-12-18.gh-issue-112938.OeiDru.rst

@@ -0,0 +1 @@
+Fix uninteruptable hang when Shell gets rapid continuous output.