docs: JSON input to JSONField is not parsed correctly

[beruic]

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

1. Create a JSONField on a serializer
2. Submit {"a": "test"} to the field through docs
3. Breakpoint at the return of JSONField.to_internal_value()

Expected behavior

The returned data is a dictionary with a single key a that has a value which is string test.

Actual behavior

The returned data is the string {"a": "test"}

[beruic]

This verified on release version 3.7.7.

[beruic]

I have narrowed this down to the point where I am confident to conclude that the issue is that the data-type attribute is set to string on the input element of the JSONField. Setting data-type to object produce the desired behaviour. Now I just need to figure out how to do just that.

[carltongibson]

Hey @beruic. Thanks for the report.

Sounds like this will be coming out of coreschema. I'm just in the process of pulling that into DRF for v3.8 now. (#5855)

There issue will be here:

https://github.com/core-api/python-coreschema/blob/494435d8fbaff12285094e99c54c38f5a1434afb/coreschema/encodings/html.py#L54-L74

I'll see if I can close this whilst I'm porting this to DRF.

[beruic]

You are right that this is related to coreschema, but the fix lies in rest_framework.schemas.inspectors.field_to_schema(). I have solved this just now in DRF. Expect a pull request soon.

I cannot however fix it for DictField, which has the same problem with input, because coreschema.schema.Object does not have an items argument for child schema like coreschema.schema.Array does. I think that a coreschema.schema.Dictionary is needed because, while coreschema.schema.Object has a properties argument, it seems to validate per key. I was considering making a feature request for coreschema, but if I understand you correctly, that is not going to be necessary, but we have to fix it in DRF.
Thoughts?

[beruic]

Just a quick update: It seems that DictField does return coreschema.Object in rest_framework.schemas.inspectors.field_to_schema(), so I may have gotten something wrong. I will see if I can get time investigating this more, but it is likely that I do not get around it again before I actually need DictField for something.

[beruic]

I just realized that I hadn't gotten anything wrong. DictField handling has been added since version 3.7.7 authored by @jlaine and committed by @carltongibson. There is no tests for this code either, and it is already in the master, so I cannot see why this PR should not be able to make it into 3.8 as well.

[beruic]

I do however see a potential bug in that the code for handling DictField does not handle the child schema.