gh-68453: Fix IDLE -s together with -c, -r or - (GH-157592)

The startup file runs in the subprocess asynchronously, so the command
or script was queued while it was still executing: an "Already
executing" dialog was shown, sys.argv was not set, and the subprocess
was restarted, discarding the startup file. Wait for the startup file
to finish first.
(cherry picked from commit 9cc3547)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: 2 people

Lib/idlelib/pyshell.py

@@ -1668,6 +1668,10 @@ def main():
         if filename and os.path.isfile(filename):
             shell.interp.execfile(filename)
     if cmd or script:
+        # Let the startup file finish first: the command or script
+        # is to run after it, in its namespace (gh-68453).
+        while shell.executing:
+            root.update()
         shell.interp.runcommand("""if 1:
             import sys as _sys
             _sys.argv = {!r}

Misc/NEWS.d/next/IDLE/2026-09-15-21-20-04.gh-issue-68453.hlxbog.rst

@@ -0,0 +1,3 @@
+Fix running IDLE with the -s option together with -c, -r or -: the command
+or script now runs after the startup file, without an error dialog and
+without restarting the shell.