Fix Enum Cyclic Ref

[feerrenrut]

Link to issue number:

Blocking PR #12500

Summary of the issue:

When creating DescriptionFor enum values, a "ValueError" can be raised.
There is a bug in the Python standard library for enum, causing a cyclic reference.
The exception is referenced by the frame.
The frame is referenced by the traceback.
The traceback is referenced by the exception.
This is detected by NVDA as an unreachable object, logging an error.

Description of how this pull request fixes the issue:

This patches the enum.Enum.__new__ method to no longer reference the exception from the frame.

Testing strategy:

Merged with #12500, ran with sample, ensured no unreachable object log error.
Unit testing this would be difficult, we'd have to install the NVDA garbageHandler, this would cause side affects for all tests.
These errors are reported to the log of system tests already.
In future we plan for system tests to fail if there are ANY errors in the log, however right now there are several
expected errors in the log on appveyor.
These first need to be resolved.
Additionally, we are in the process of resolving a tricky intermittent failure for system tests.
Once the intermittent failure is resolved we can look to make the tests more strict.

Known issues with pull request:

None

Change log entries:

None

Code Review Checklist:

• Pull Request description is up to date.
• Unit tests.
• System (end to end) tests.
• Manual testing.
• User Documentation.
• Change log entry.
• Context sensitive help for GUI changes.
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers

[feerrenrut]

A diff of the python standard library implementation vs the replacement implementation:
stdLibVsNew.txt

[michaelDCurran]

Would it not be better for maintainability that replacement__new__ is simply:

if value not in cls.__members__.values():
    raise ValueError(f"{value} is not a supported value of {cls}")
return old__new__(value)

Though obviously what you wrote will be useful for a pr against cPython.
But other than the other corrections I and @lukaszgo1 have mentioned, I'd be happy to approve with the code you have here.

[feerrenrut]

Would it not be better for maintainability that replacement__new__ is simply

I'm trying to maintain compatibility with the built-in enum behavior. There are a number of other values that it accepts for various reasons. Using the suggestion would mean that only values for the enum are accepted.