Disabled TagField messes data up

[alice-telescoop]

If the tags are set to for instance "tag1", "tag2" and a form TagField is set as disabled, the data that is sent to clean does not go through the widget's format_value method so it is '[<Tag: "tag1">, <Tag: "tag2">]' which is then parsed and saves the wrong data.

A quick fix I did in my project is to add

if self.disabled:
    return value

at the beginning of the clean form field method. In my project I inherited the widget to do that. In the module it may be better to fix the issue upstream, but here is the bug

[SparshGarg999]

I was able to reproduce this issue locally. When TagField has disabled=True, Django bypasses POST/GET data and passes the field's initial value directly into clean(self, value).

When used with a ModelForm (or initialized with a QuerySet / list of Tag model instances), super().clean(value) converts the list of Tag objects to str(value), resulting in '[<Tag: tag1>, <Tag: tag2>]', which parse_tags() parses into corrupted tags like '[<Tag: tag1>' and '<Tag: tag2>]'.

When self.disabled is True, clean(self, value) should check if value is not a string (or if value is already an iterable of Tag instances or empty) and return it directly (or parse strings if initial was provided as a string).

I'll submit a PR with the fix and unit test coverage for disabled TagField in ModelForms and standalone forms.