[WFS] Wrong geometry type for layer / missing Mixed Geometry WFS Support

[pathmapper]

What is the bug or the crash?

Wrong geometry type for layer from WFS:

The following request returns a collection: 10 features in total - 3 polygons and 7 points:

https://xplanung.freiburg.de/xplansyn-wfs/services/xplansynwfs?SERVICE=WFS&REQUEST=GetFeature&VERSION=2.0.0&TYPENAMES=xplan:BP_AnpflanzungBindungErhaltung&COUNT=15000&SRSNAME=EPSG:25832

But a polygon layer is added to the Layers widget:

https://user-images.githubusercontent.com/20856381/178444248-988b710a-b8f6-4250-ac30-c1ec8aef481e.mp4

Steps to reproduce the issue

1. Add the following WFS connection to QGIS browser: https://xplanung.freiburg.de/xplansyn-wfs/services/xplansynwfs
2. Add the feature type: xplan:BP_AnpflanzungBindungErhaltung
3. See error: A polygon layer is added, only 3 polygons are visible, feature count and attribute table shows 10 features.

Versions

QGIS version	3.27.0-Master	QGIS code revision	876188b627
Qt version	5.12.8
Python version	3.8.10
GDAL/OGR version	3.0.4
PROJ version	6.3.1
EPSG Registry database version	v9.8.6 (2020-01-22)
Compiled against GEOS	3.8.0-CAPI-1.13.1	Running against GEOS	3.8.0-CAPI-1.13.1
SQLite version	3.31.1
PostgreSQL client version	12.11 (Ubuntu 12.11-0ubuntu0.20.04.1)
SpatiaLite version	4.3.0a
QWT version	6.1.4
QScintilla2 version	2.11.2
OS version	Ubuntu 20.04.4 LTS

Active Python plugins sagaprovider | 2.12.99 grassprovider | 2.12.99 MetaSearch | 0.3.6 processing | 2.12.99 db_manager | 0.1.20

Supported QGIS version

• [X] I'm running a supported QGIS version according to the roadmap.

New profile

• [X] I tried with a new QGIS profile

Additional context

Same result if layer is added via Data Source Manager.

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If the response GML (xplansynwfs.zip) is added via drag and drop to QGIS, two layers with correct geometry type and feature count are added:

[pathmapper]

In case the above example doesn't work anymore:

Another publicly available WFS which is serving mixed geometry types for a feature type resulting in incorrect layer geometry type when loading into QGIS via WFS connection:

WFS endpoint: http://xplanung.lkee.de/xplansyn-wfs/services/xplansynwfs

Feature type: xplan:BP_AnpflanzungBindungErhaltung

[pathmapper]

Ideally QGIS would require you to manually select which geometry type(s) you want to load from a mixed geometry WFS source into the project like it is already the case for other sources which support mixed geometry types (https://github.com/qgis/QGIS/pull/49334#issuecomment-1182580051).

Another option would be to automatically load the features with different geometry types in multiple layers according to the geometry type.

I think the difficulty with WFS sources compared to other sources might be that it could be the case that you don't know which geometry types you'll get from a WFS for a certain feature type until the full response document is received - this doesn't play well with e.g. WFS paging.