Add option to provide a callable for PolymorphicProxySerializer.serializers

[glennmatthews]

Adding a minor feature that we found useful in our own use of PolymorphicProxySerializer - the ability to initialize it with a callable (such as a lambda) that returns a list/dict of serializers when evaluated, rather than needing to provide the list of serializers up front at declaration time.

In our case this was useful because we have a polymorphic schema method field that can return a serializer corresponding to any subclass of a given abstract base model, not all of which may already be defined/imported at the time the field is declared. Being able to provide a callback that can be deferred until the time the schema is actually generated made our implementation easier.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (eeb8a11) 98.61% compared to head (2828132) 98.63%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #953      +/-   ##
==========================================
+ Coverage   98.61%   98.63%   +0.01%     
==========================================
  Files          68       68              
  Lines        8074     8110      +36     
==========================================
+ Hits         7962     7999      +37     
+ Misses        112      111       -1     

Impacted Files	Coverage Δ
drf_spectacular/contrib/django_filters.py	90.44% <100.00%> (+0.73%)	⬆️
drf_spectacular/utils.py	99.57% <100.00%> (+0.01%)	⬆️
tests/contrib/test_django_filters.py	100.00% <100.00%> (ø)
tests/test_polymorphic.py	100.00% <100.00%> (ø)

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[tfranzel]

@glennmatthews, awesome stuff! That make it even more meta 😆, I like it!

Just one thought, do you think providing arguments is superfluous? (e.g. self a.k.a. instance of PolymorphicProxySerializer).

Not sure if this adds something, you have seen this pattern recurring. What do you think? Just a question, not a change request.

[tfranzel]

Whatever, let's just merge it. We have a method to tack on optional kwargs to this callback. Still interested in your opinion though.

drf-spectacular/drf_spectacular/plumbing.py

Line 1338 in e98b0c6

def filter_supported_arguments(func, **kwargs):

[glennmatthews]

Thus far I haven't seen any need to pass args into the callable, but I like the way you're thinking. :-) Thanks for the approval and merge!