Fix loading providers hooks fields w/o FAB provider installed

[jscheffl]

closes: #55841
related: #57555 #49446

Sorry that I was not actively enough paying attention that the contributed mocking of provider forms w/o Fab was not working. I thought it was fixed by #49446 and did not test explicitly myself. Raising awareness in the bug #55841 now made me a follow-up fix.

This PR reverts mostly the changes made by #49446 as the original code was "almost" working, just did not consider that mocking the WTForms and FAB classes only works if the modules are really installed. The mock is now extended to mock the modules to tell the system they are available before mocking. If installed just mocks will be applied to load fields, if WTForms, FAB and flask_babel are not installed the system is patched to assume they are existing.

How to test the fix:
Best Option: Patch the single file into an installation and check if it is working
Alternative:

• Start based on this branch via breeze start-airflow --python 3.12 --load-example-dags --backend postgres --executor LocalExecutor --answer y and then log on to the UI. To to admin -> connections and see all is working. No surprise FAB is installed per default. Then log out and stop API server in the tmux panel. Then remove the FAB provider and tooling via uv pip uninstall WTForms apache-airflow-providers-fab flask_appbuilder flask_babel in the panel where API server is stopped. Restart API Server and logon the UI again. Double check that on Admin->Providers the FAB provider is non existing. Then check Admin->Connections and Add a connection if fields are populated, e.g. from Airbyte

[potiuk]

Looks good :) . I thought we can do it indeed.

[potiuk]

I tested it locally:

Before the fix (main):

1. run breeze start-airflow --load-example-dags --load-default connections --db-reset
2. Ctrl-C api-server
3. unistall fab provider uv pip uninstall ./providers/fab
4. uninstall wtforms and flask_babel uv pip uninstall wtforms flask_babel flask_appbuilder

root@7a9fe2c838c8:/opt/airflow# uv pip uninstall ./providers/fab/
Using Python 3.10.19 environment at: /usr/python
Uninstalled 1 package in 39ms
 - apache-airflow-providers-fab==3.0.1 (from file:///opt/airflow/providers/fab)
root@7a9fe2c838c8:/opt/airflow# uv pip uninstall wtforms flask_babel flask_appbuilder
Using Python 3.10.19 environment at: /usr/python
Uninstalled 3 packages in 116ms
 - flask-appbuilder==5.0.1
 - flask-babel==4.0.0
 - wtforms==3.2.1

5. restart api-server (airflow api-server)
6. try to edit an aws connection and see custom fields

Result:

a lot of errors in log:

flow.providers_manager] loc=providers_manager.py:949
2025-11-02T23:55:11.515303Z [info     ] The hook_class 'airflow.providers.opsgenie.hooks.opsgenie.OpsgenieAlertHook' is not fully initialized (UI widgets will be missing), because the 'flask_appbuilder' package is not installed, however it is not required for Airflow components to work [airflow.providers_manager] loc=providers_manager.py:949
2025-11-02T23:55:11.551442Z [info     ] The hook_class 'airflow.providers.oracle.hooks.oracle.OracleHook' is not fully initialized (UI widgets will be missing), because the 'flask_appbuilder' package is not installed, however it is not required for Airflow components to work [airflow.providers_manager] loc=providers_manager.py:949

After the fix

1. Checkout 57717 (gh co 57717)
2. Repeat points 1-6 above

Result:

No errors in log.

(Polish UI ... sorry :) )

[jscheffl]

(Polish UI ... sorry :) )

Polish UI... cool!

[pierrejeambrun]

@jscheffl Probably need a backport

[jscheffl]

@jscheffl Probably need a backport

Not probably, but seriously. Thanks for the hint, was almost lost in work stack and forgotten. PR linked...