gh-85604: Check IDLE theme colors at startup

An invalid color in a user highlight theme crashed the Settings dialog. Now it is ignored with a warning and the default color is used instead.
serhiy-storchaka · Sep 16, 2026 · Sep 16, 2026 · Sep 16, 2026 · fd6f990b0ddf153494ca47c106e905b619960346
commit fd6f990b0ddf153494ca47c106e905b619960346
diff --git a/Lib/idlelib/idle_test/test_pyshell.py b/Lib/idlelib/idle_test/test_pyshell.py
@@ -4,8 +4,10 @@
 from idlelib import pyshell
 import os
 import unittest
-from test.support import requires
+from unittest import mock
+from test.support import requires, captured_stderr
 from tkinter import Tk
+from idlelib import config
 
 
 class FunctionTest(unittest.TestCase):
@@ -38,6 +40,47 @@ def test_fix_user_path(self):
         eq(pyshell.fix_user_path([idlelib_dir]), [])
 
 
+class CheckThemeColorsTest(unittest.TestCase):
+
+    @classmethod
+    def setUpClass(cls):
+        requires('gui')
+        cls.root = Tk()
+        cls.root.withdraw()
+
+    @classmethod
+    def tearDownClass(cls):
+        cls.root.update_idletasks()
+        cls.root.destroy()
+        del cls.root
+
+    def test_check_theme_colors(self):
+        # gh-85604: invalid colors are reported and removed.
+        cfg = config.IdleUserConfParser('')
+        cfg.SetOption('Good', 'keyword-foreground', '#ff7700')
+        cfg.SetOption('Bad', 'keyword-foreground', 'bpo-00224')
+        cfg.SetOption('Bad', 'keyword-background', 'white')
+        cfg.SetOption('Bad', 'comment-background', '#12345')
+        with (mock.patch.dict(pyshell.idleConf.userCfg, {'highlight': cfg}),
+              captured_stderr() as stderr):
+            pyshell.check_theme_colors(self.root)
+        msg = stderr.getvalue()
+        self.assertIn("invalid color 'bpo-00224' for 'keyword-foreground' "
+                      "in theme 'Bad'", msg)
+        self.assertIn("invalid color '#12345'", msg)
+        self.assertNotIn('Good', msg)
+        self.assertNotIn('white', msg)
+        self.assertFalse(cfg.has_option('Bad', 'keyword-foreground'))
+        self.assertFalse(cfg.has_option('Bad', 'comment-background'))
+        self.assertTrue(cfg.has_option('Bad', 'keyword-background'))
+        self.assertTrue(cfg.has_option('Good', 'keyword-foreground'))
+        # Nothing left to report.
+        with (mock.patch.dict(pyshell.idleConf.userCfg, {'highlight': cfg}),
+              captured_stderr() as stderr):
+            pyshell.check_theme_colors(self.root)
+        self.assertEqual(stderr.getvalue(), '')
+
+
 class PyShellFileListTest(unittest.TestCase):
 
     @classmethod

@@ -408,6 +408,26 @@ def restart_line(width, filename):  # See bpo-38141.
         return tag[:-2]  # Remove ' ='.
 
 
+def check_theme_colors(root):
+    """Warn about invalid colors in user themes and remove them.
+
+    The default colors are then used instead (gh-85604).  The user
+    files are not changed until the settings are saved.
+    """
+    cfg = idleConf.userCfg['highlight']
+    for theme in cfg.sections():
+        for element in cfg.options(theme):
+            color = cfg.Get(theme, element)
+            try:
+                root.winfo_rgb(color)
+            except TclError as err:
+                print(f'Warning: ignoring invalid color {color!r} '
+                      f'for {element!r} in theme {theme!r}: {err}. '
+                      f'Please reconfigure it in the IDLE Settings dialog.',
+                      file=sys.stderr)
+                cfg.RemoveOption(theme, element)
+
+
 def fix_user_path(path):
     """Return path without the idlelib directory (gh-134300).
 
@@ -1617,6 +1637,7 @@ def main():
     if config_error:
         messagebox.showwarning('IDLE Configuration Warning', config_error,
                                parent=root)
+    check_theme_colors(root)
 
     # set application icon
     icondir = os.path.join(os.path.dirname(__file__), 'Icons')

diff --git a/Misc/NEWS.d/next/IDLE/2026-09-16-12-00-00.gh-issue-85604.badclr.rst b/Misc/NEWS.d/next/IDLE/2026-09-16-12-00-00.gh-issue-85604.badclr.rst
@@ -0,0 +1,3 @@
+Invalid colors in user highlight themes no longer crash the IDLE Settings
+dialog. They are now reported at IDLE startup and replaced with the default
+colors.