Fix mismatched traceback in pythonrc.py injection

[CNSeniorious000]

Since vscode-python injects PYTHONSTARTUP into pythonrc.py to show the "Ctrl click to launch VS Code Native REPL" message, traceback always shows lines inside pythonrc.py in the interactive console.

Example:

That's because python sets __main__ to the pythonrc.py module, which has a __loader__ attribute. The __loader__ object is then exposed in the global namespace of the interactive console. However, linecache uses __loader__ to get the source code, causing the mismatch.

After this PR, the traceback points to the right source now:

In the _pyrepl.__main__ module, there was some comment mentioning this behavior and they set __loader__ = None to avoid this. See python/cpython#129098 for more information

[Copilot]

Pull request overview

This PR fixes a traceback mismatch issue in the Python interactive console caused by VS Code's pythonrc.py injection. When PYTHONSTARTUP points to pythonrc.py, Python exposes the module's __loader__ in the global namespace, which causes linecache to incorrectly display tracebacks pointing to pythonrc.py instead of the actual source files.

Key Changes:

• Sets __spec__ and __loader__ to None in pythonrc.py to prevent linecache from caching this file
• Adds an explanatory comment documenting why these attributes are set to None

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The comment has a grammatical error. It should say "incorrectly reporting tracebacks" instead of "incorrectly report tracebacks".

Suggested change

	# Avoid caching this file by linecache and incorrectly report tracebacks.
	# Avoid caching this file by linecache and incorrectly reporting tracebacks.

[Copilot]

The new behavior of setting __spec__ and __loader__ to None should have test coverage to ensure that these attributes are properly set and that they prevent linecache from incorrectly caching this file. Consider adding a test that verifies these attributes are None after module import.

[eleanorjboyd]

Hi @CNSeniorious000! Sorry for the delay on getting around to this, two items:

1. can you create an issue and tag it in this PR, that way we can better track the fix through our release process
2. the failing smoke tests should no longer appear after this new run as that was a flaky test we skipped for now