michael-s-molina opened a new pull request, #37252:
URL: https://github.com/apache/superset/pull/37252
### SUMMARY
Fixes a bug where the MCP service would corrupt Flask-AppBuilder's shared
`appbuilder` singleton, causing `BuildError: Could not build url for endpoint
'None.login'` errors when accessing Superset.
**Root Cause:**
PR #37190 (`fix(mcp): push Flask app context in mcp_auth_hook for tool
execution`) added `from superset.mcp_service.flask_singleton import
get_flask_app` to `auth.py`. During main app initialization, when MCP tools are
decorated with `@tool` (which uses `mcp_auth_hook`), this import triggers
`flask_singleton.py` to be loaded. The `flask_singleton.py` module then calls
`create_app()` creating a second Flask app that re-initializes the shared
`appbuilder` singleton.
When `appbuilder.init_app()` is called a second time:
1. Flask-AppBuilder's `add_view_no_menu()` detects the view class is already
registered
2. It returns a **new instance** without calling `create_blueprint()` (which
sets the `endpoint` attribute)
3. The view's `endpoint` remains `None`
4. When the main app tries to build URLs (e.g., `get_url_for_login`), it
fails with `BuildError`
**The Fix:**
Modified `superset/mcp_service/flask_singleton.py` to check if
`appbuilder.app` is already initialized. If so, it reuses the existing Flask
app instead of creating a new one via `create_app()`. This prevents corruption
of the shared appbuilder singleton.
```python
# Before: Always created a new app
_temp_app = create_app()
# After: Reuse existing app if appbuilder is already initialized
if appbuilder.app is not None:
app = appbuilder.app
else:
_temp_app = create_app()
# ... initialization code
```
### TESTING INSTRUCTIONS
1. Enable MCP service in your Superset configuration
2. Start Superset in debug mode: `superset run -p 8088 --reload --debugger`
3. Navigate to `http://localhost:8088/superset/welcome/`
4. Verify the login page loads without errors
5. Verify you can log in successfully
### ADDITIONAL INFORMATION
<!--- Check any relevant boxes with "x" -->
<!--- HINT: Include "Fixes #nnn" if you are fixing an existing issue -->
- [ ] Has associated issue:
- [ ] Required feature flags:
- [ ] Changes UI
- [ ] Includes DB Migration (follow approval process in
[SIP-59](https://github.com/apache/superset/issues/13351))
- [ ] Migration is atomic, supports rollback & is backwards-compatible
- [ ] Confirm DB migration upgrade and downgrade tested
- [ ] Runtime estimates and downtime expectations provided
- [ ] Introduces new feature or API
- [ ] Removes existing feature or API
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