overrides on django filters only work the first request

[wgiddens]

Describe the bug
When using extend_schema_field to override the description on a django_filter filter, the overridden description only works for the first request.

To Reproduce
Create a custom filter and override description.

For example:

@extend_schema_field({"description": "overridden description"})
class CustomBooleanFilter(BooleanFilter):
    pass

View the schema multiple times. It will show overridden description only on the 1st request.

Expected behavior
It should always use the overridden schema.

I think this is because the description gets popped from the schema object in resolve_filter_field. Unless there is a use case I'm not thinking of, that should probably be a schema.get().

It looks like enum and readOnly get popped as well. They probably have the same issue.

[tfranzel]

Hi @wgiddens good catch, but this all happens for a reason.

• description is popped because it gets reinserted one level up. the schema itself is nested in the parameter object. the description is on the top level
• enum is written back into the schema 2 lines down. so basically irrelevant for your argument.
• readOnly gets popped because its makes little sense for parameters. this is a remnant of model synthesis.

Sure, this could all be written differently but we usually start from a scratch schema that gets refined along the way. I think the actual issue is that we break isolation by not making a copy here. All other branches start from a fresh (and isolated) schema object.

drf-spectacular/drf_spectacular/contrib/django_filters.py

Line 99 in eeb8a11

schema = annotation

Note however that by decorating a raw schema, you essentially throw away the inferred type information. Raw schema means: "Get out of the way, I know what I am doing." In that case we just do some trimming, nothing more.

[wgiddens]

That makes sense. Copying the annotation here fixes it. I opened a PR here: #951

[tfranzel]

added a test case that checks for the modification. thanks @wgiddens for the PR