gh-82183: Do not restart the busy IDLE shell when running without restart

"Run... Customized" with "Restart shell" unchecked restarted the shell
anyway when it was busy executing code, killing any pending input.  It now
reports that the shell is executing and does not run.

Author: serhiy-storchaka

Lib/idlelib/idle_test/test_runscript.py

@@ -2,6 +2,7 @@
 
 from idlelib import runscript
 import unittest
+from unittest import mock
 from test.support import requires
 from tkinter import Tk
 from idlelib.editor import EditorWindow
@@ -28,6 +29,26 @@ def test_init(self):
         sb = runscript.ScriptBinding(ew)
         ew._close()
 
+    def test_run_module_event_shell_busy_no_restart(self):
+        # gh-82183: running without restarting the busy shell aborts.
+        ew = EditorWindow(root=self.root)
+        sb = runscript.ScriptBinding(ew)
+        sb.getfilename = mock.Mock(return_value='test.py')
+        sb.checksyntax = mock.Mock(return_value='code')
+        sb.tabnanny = mock.Mock(return_value=True)
+        sb.shell = shell = mock.Mock()
+        shell.executing = True
+        interp = shell.interp
+        with mock.patch.object(runscript, 'CustomRun') as customrun:
+            # Restart shell unchecked.
+            customrun.return_value.result = (['arg'], False)
+            result = sb.run_module_event(None, customize=True)
+        self.assertEqual(result, 'break')
+        interp.display_executing_dialog.assert_called_once()
+        interp.restart_subprocess.assert_not_called()
+        interp.runcode.assert_not_called()
+        ew._close()
+
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)

Lib/idlelib/runscript.py

@@ -139,6 +139,10 @@ def run_module_event(self, event, *, customize=False):
                 return 'break'
         self.cli_args, restart = run_args if customize else ([], True)
         interp = self.shell.interp
+        if self.shell.executing and not restart:
+            # Cannot run without restarting the busy shell (gh-82183).
+            interp.display_executing_dialog()
+            return 'break'
         if pyshell.use_subprocess and restart:
             interp.restart_subprocess(
                     with_cwd=False, filename=filename)

Misc/NEWS.d/next/IDLE/2026-07-01-19-00-00.gh-issue-82183.rNsTrt.rst

@@ -0,0 +1,3 @@
+When the shell is busy running code, using "Run... Customized" with "Restart
+shell" unchecked now reports that the shell is executing instead of
+restarting it anyway.