Mark Snowflake connection form Proxy Port field optional

[nikhilcss97]

Summary

Fixes a silent Save failure on the Snowflake connection form in the Airflow
web UI when the Proxy Port field is left blank.

SnowflakeHook.get_connection_form_widgets currently declares the field as:

"proxy_port": IntegerField(lazy_gettext("Proxy Port")),

IntegerField without Optional() fails WTForms validation on empty input
because an empty string cannot be coerced to int. FAB then silently
re-renders the form without persisting any changes, so the Save button
appears to do nothing when the optional proxy fields are not filled in.

Meanwhile the runtime (SnowflakeHook._get_conn_params) already treats
proxy_port as optional and only applies it when truthy, and every non-UI
path (CLI, env-vars, REST API, secrets backends) accepts an absent
proxy_port. The UI was the only code path enforcing it, and unintentionally.

Fix

Add validators=[Optional()] to the proxy_port widget so WTForms
short-circuits validation for empty input. Also attach BS3TextFieldWidget()
to match the style of the other proxy widgets.

from wtforms.validators import Optional

"proxy_port": IntegerField(
    lazy_gettext("Proxy Port"),
    widget=BS3TextFieldWidget(),
    validators=[Optional()],
),

Tests

Added test_get_connection_form_widgets_proxy_port_is_optional in
providers/snowflake/tests/unit/snowflake/hooks/test_snowflake.py covering:

• Optional() is present in the proxy_port field validators
• a bound form validates with proxy_port="" and coerces to None
• a bound form validates with proxy_port="8080" and coerces to 8080
• a bound form does not validate with a non-integer value, so integer
  type-checking is preserved

Reproduction (pre-fix)

1. Install Airflow 2.11.x with apache-airflow-providers-snowflake>=6.9.0.
2. In the UI: Admin → Connections → Add a new record, choose
   Snowflake, fill in the required fields, leave the four Proxy fields
   blank.
3. Click Save. The form re-renders with no flash message; the
   connection is not created.
4. Re-enter any integer (e.g. 0) in Proxy Port and click Save. The
   connection is created.

Post-fix: step 3 succeeds, and step 4 is no longer necessary.

Scope and safety

• Behavior-only change to the FAB/WTForms widget layer. Runtime hook
  behavior is unchanged because _get_conn_params already guards on
  if proxy_port:.
• No accepted input is narrowed: non-UI paths already accepted empty
  proxy_port; this aligns the UI with them.
• Integer type-checking for non-empty input is preserved via the negative
  test case.

Related

• Proxy support feature: Add proxy support for Snowflake Connections #59078
• Proxy implementation: reformat add proxy support commit #60432
• conn-fields migrated to YAML in 6.10.0: Add missing conn-fields for providers migrated to yaml #62116
• Proxy fields docs update: Update snowflake hook docs to reflect snowflake hook proxy fields support #63486

closes: #65443

---

Was generative AI tooling used to co-author this PR?

• Yes (Claude Sonnet)

Generated-by: Claude Sonnet following the guidelines

---

• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst, in airflow-core/newsfragments. You can add this file in a follow-up commit after the PR is created so you know the PR number.

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

---

• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst, in airflow-core/newsfragments. You can add this file in a follow-up commit after the PR is created so you know the PR number.

[boring-cyborg]

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[potiuk]

Pending CI passes.