fix: editing of FlagField via EnumFlagField form field

[crgwbr]

When attempting to edit an EnumFlagField through a model form (e.g. in django admin), the form would always be invalid on submit with an invalid_choice error. This was due to the form attempting to set the model field to a list of enum members (rather than bitwise-OR'ing the flags together).

This change handles this case by overriding FlagField._coerce_to_value_type and performing the appropriate bitwise OR there.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.

Project coverage is 99.87%. Comparing base (4a1688d) to head (549a1f1).

Files with missing lines	Patch %	Lines
src/django_enum/forms.py	96.15%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main      #97      +/-   ##
===========================================
- Coverage   100.00%   99.87%   -0.13%     
===========================================
  Files            9        9              
  Lines          806      831      +25     
  Branches       117      123       +6     
===========================================
+ Hits           806      830      +24     
- Partials         0        1       +1     

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[bckohan]

bug confirmed #102

[bckohan]

Thank you for the report and contribution @crgwbr!

I'm going to move your _coerce_to_value_type implementation over to the form class. This is because we delegate all EnumField construction logic to the Enum's constructor. Custom construction logic may be implemented in Enum._missing_ - it could be the case that an enum decides to do something different with a sequence of values and users would not expect setting the model field to behave differently. The bug really resides in the django_enum.forms.EnumFlagField class.

[crgwbr]

Thanks for improving and merging this, @bckohan! Would you possibly be able to cut a patch release with this fix soon? Hoping to remove from my project the temporary monkey patch I used to workaround the bug.

[bckohan]

Yes, I'm hoping to get one out this weekend - a few other fixes are in progress wrt how the forms work by default.