Using pyfakefs breaks vscode's debugger

[Aran-Fey]

Using pyfakefs leads to a variety of issues with vscode's debugger, like breakpoints not working and duplicate file tabs being opened. I made a bug report here, but the folks at debugpy have decided it's not their responsibility to fix it. Can you guys take care of it?

[Aran-Fey]

This may only be an issue if PatchMode.AUTO is used, now that I think about it.

[mrbean-bremen]

Yeah, PatchMode.AUTO may have unwanted side effects and probably won't play nice with a debugger, as that relies on loading code on a low level.
If this indeed only happens if patching open_code, there is probably not much we can do with reasonable effort. I don't think I want to go down that rabbit hole...

[mrbean-bremen]

@Aran-Fey - can you confirm that this only happens with PatchMode.AUTO?

[Aran-Fey]

Actually, nope. A duplicate tab is opened regardless of the PatchMode, and the breakpoints continue to sometimes be ignored without any apparent reason.

[mrbean-bremen]

Ok, thanks. I'm not using VSCode (I use PyCharm), so it may take a while to understand this. Do you have a way to reproduce this with some minimal example?

[Aran-Fey]

This seems to do it:

import typing

def test_demo(fs):
    typing.get_type_hints(int)

1. Set a breakpoint at typing.get_type_hints(int) -> breakpoint is hit, duplicate file tab is opened
2. Set a breakpoint inside of get_type_hints -> breakpoint is ignored
3. Remove fs fixture: Both issues go away

[mrbean-bremen]

Thanks, I will give it a try!

[mrbean-bremen]

You are working with the current pyfakefs version (5.7.1), right?

[mrbean-bremen]

Ah, and which Python version are you using?

[Aran-Fey]

Correction: Only the duplicate tab issue goes away. Having some trouble reproducing the breakpoint issue. If I replace typing with a custom-made python module, the breakpoint is hit as expected. Maybe breakpoints don't work in the stdlib or something, or maybe it's just the bug being janky again. Really not sure.

I'm using pyfakefs 5.7.1 and cpython 3.10.13.

[mrbean-bremen]

So far, I have not been able to get sensible behavior even in tests without pyfakefs - I guess I have to better understand the workflow in VSCode first... Will have another go over the weekend.

[mrbean-bremen]

Ok, I persuaded VSCode to work for me, and I can reproduce the duplicate tab behavior now (not the ignored breakpoint so far). At the moment, I have no idea where to even look, so no promises...

[mrbean-bremen]

@Aran-Fey - can you please check the behavior with the main branch?

[Aran-Fey]

The issue with the read-only tabs is fixed. Not sure about the other one, but this is definitely much better than before.

[mrbean-bremen]

I have not been able to reproduce the breakpoint issue, so if you encounter it again and know how to reproduce it, let me know. Otherwise I will probably make a new release with the fix soon, if nothing else comes up.