Just released WTForms 3.1.0 break FAB widgets (including just released 4.3.8)

[potiuk]

The WTForms 3.1.0 introduced a change that breaks implementation of Flask App Builder choices fields based on QuerySelectField.

The problem is that the new choices widget returns now possible "render_kwargs" parameter in "iter_choices" :

See the release notes for 3.1.0

• https://wtforms.readthedocs.io/en/3.1.x/changes/#version-3-1-0

The issue in WTForms is: pallets-eco/wtforms#692
The PR in WTForms is: https://github.com/wtforms/wtforms/pull/739/files

the change is that "choices" widget expects now 4 values to unpack in SelectFieldBase.iter_choices (value, label, selected, render_kw) where previously there were three (value, label, selected). Unfortunately Flask App builder overrides implementation of the iter_choices in QuerySelectField

Flask-AppBuilder/flask_appbuilder/fields.py

Line 131 in 38180b0

def iter_choices(self):

- the iter_choices method still returns 3 values which means that when core WTF iterates over the field to display their value here: https://github.com/wtforms/wtforms/pull/739/files#diff-70bc7290d3bd4ce3f5436885709a6b8af1086763e4699598e578ee809027eadbR365 it fails with

>           for val, label, selected, render_kw in field.iter_choices():
E           ValueError: not enough values to unpack (expected 4, got 3)

Environment

Flask-Appbuilder version: Tested with 4.3.6, 4.3.7, 4.3.8 (but previous versions are also affected)
WTForms 3.1.0

pip freeze output:

pip freeze | grep -E "(Flask-App|WTForms)"

Flask-AppBuilder==4.3.8
WTForms==3.1.0

Describe the expected results

When instantiating any choice widgets in WTForms 3.1.0 and installing QuerySelectMultipleField

>           for val, label, selected, render_kw in field.iter_choices():
E           ValueError: not enough values to unpack (expected 4, got 3)

What should happen - it should not raise the exception.

I am not sure how to easily - minimally - reproduce it but the root cause of the problem is quite clear - It has been detected by the canary build in Apache Airflow (when WTForms got automatically upgraded to 3.1.0 which is compatible with FAB). FAB has WTForms<4, so anyone installing new FAB with latest compatible WTFOrms will have this problem.

You can see example failure here: https://github.com/apache/airflow/actions/runs/6516454013/job/17700187383#step:6:12162

However simply using and displaying QuerySelectMultipleField should trigger it.