Fix Notification Source edit form base class and Provider widget (#332)

[jvanderaa]

Closes #332.

Problem

NotificationSourceForm subclassed django.forms.ModelForm rather than NautobotModelForm, so none of the Nautobot form mixins applied. Two user-visible consequences:

• Custom fields were silently omitted. NotificationSource is an OrganizationalModel, which includes CustomFieldModel — so custom fields can be defined on it — but CustomFieldModelFormMixin only arrives via NautobotModelForm. The edit form rendered a single field regardless of any custom fields configured.
• Providers had no search. The auto-generated ModelMultipleChoiceField rendered every Provider as an <option> on each edit page load, instead of the API-backed selector used elsewhere in the app.

The viewset half of #332 was already resolved by #344; this is the remaining form half that @gsnider2195 called out in the issue ("wrong base class", "wrong widget for providers field").

Change

class NotificationSourceForm(NautobotModelForm):
    providers = DynamicModelMultipleChoiceField(queryset=Provider.objects.all(), required=False)

This matches CircuitImpactForm, CircuitMaintenanceForm, and NoteForm in the same module; both imports were already present.

required=False is required, not incidental — an explicitly declared form field bypasses fields_for_model, so the model's blank=True does not propagate and Providers would otherwise become mandatory.

Why fields stays an explicit list

Switching to NautobotModelForm activates the nb-use-fields-all pylint check, which asks for fields = "__all__". Following that here would be a bug, so the rule is suppressed with the rationale recorded inline.

name and attach_all_providers are owned by PLUGINS_CONFIG: import_notification_sources() runs on every post_migrate, re-applies attach_all_providers from config, and deletes any Notification Source whose name is absent from the config. Exposing name in the UI would let a rename silently delete the object on the next migrate. This matches the documented behavior in docs/user/app_getting_started.md — "you can only view and edit providers". providers is the only safely user-editable field.

Testing

Adds nautobot_circuit_maintenance/tests/test_forms.py, written test-first — both tests were confirmed failing against the old form before the fix ('cf_…' not found in {'providers': ModelMultipleChoiceField} and ModelMultipleChoiceField is not an instance of DynamicModelMultipleChoiceField).

It extends FormTestCases.BaseFormTestCase, which also contributes a query_params validation guard for any DynamicModelChoice field added later.

• invoke unittest --label nautobot_circuit_maintenance.tests.test_forms → 3 tests OK (1 inherited test skips: providers declares no query_params).
• Full suite → 296/297. The one failure is test_basics.TestVersion ('3.0.1a0' != '3.1.2a0'), which reproduces identically on a pristine develop checkout — a stale app version in the local container image, unrelated to this change.
• invoke pylint → 10.00/10; ruff check / ruff format --check clean.

Follow-up (not in this PR)

NotificationSourceFilterSetForm (same module, wired as filterset_form_class on the same viewset) is still on BootstrapMixin, forms.ModelForm and should be a NautobotFilterForm. It also exposes only q, while NotificationSourceFilterSet supports filtering on name, providers, attach_all_providers, tags, and created — so the list view cannot filter by Provider today. That is a behavior change rather than a bug fix, so it is left out of this PR; happy to open a separate issue. It is also the last class keeping the file-level nb-incorrect-base-class suppression alive.

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
nautobot_circuit_maintenance
forms.py
Project Total

This report was generated by python-coverage-comment-action

[glennmatthews]

Fix looks valid as far as it goes but I think we may need to go further.

[glennmatthews]

How does this work for the create case that is also provided by NotificationSourceUIViewSet? Do we need to disable the create action/view entirely?