Trouble Adding Rings to Polygons in Vector Layers: Works Inconsistently

[Ipickedausername]

What is the bug or the crash?

Hello,

I am working with a SpatiaLite layer in CRS 2154 (the same as the project's CRS) with a Multi-polygon geometry type.
When I attempt to add a ring inside a polygon, it works inconsistently.

Most of the time, if the process fails, creating another ring with fewer vertices and/or a smaller ring, will resolve the issue about 90% of the time.

I have tested this on other SpatiaLite layers with Polygon geometry, on Shapefile layers, and in different projects, but the issue persists.

Steps to reproduce the issue

The issue is easy to reproduce; we simply need to add a ring with many vertices.
However, it seems very difficult to identify a pattern (number of vertices, shape of the ring, size of the ring).

Here are two pictures to show that the ring creation is possible within the same polygon, despite the error message.

And, here is a test project where I can reproduce this issue.
Test_project.zip

Versions

<style type="text/css"> p, li { white-space: pre-wrap; } </style>

Version de QGIS	3.38.3-Grenoble	Révision du code	37f9e6e
Version de Qt	5.15.13
Version de Python	3.12.6
Version de GDAL/OGR	3.9.2
Version de Proj	9.4.0
Version de la base de données du registre EPSG	v11.004 (2024-02-24)
Version de GEOS	3.12.2-CAPI-1.18.2
Version de SQLite	3.45.1
Version de PDAL	2.6.3
Version du client PostgreSQL	16.2
Version de SpatiaLite	5.1.0
Version de QWT	6.2.0
Version de QScintilla2	2.14.1
Version de l'OS	Windows 10 Version 2009
Extensions Python actives
GroupStats	2.2.7
mapswipetool_plugin	1.3
networks	2.7.19
OpenTopography-DEM-Downloader	2.0
qfieldsync	v4.9.1
quick_map_services	0.19.34
db_manager	0.1.20
grassprovider	2.12.99
processing	2.12.99

Version de QGIS 3.38.3-Grenoble Révision du code [37f9e6e](https://github.com/qgis/QGIS/commit/37f9e6efee) Version de Qt 5.15.13 Version de Python 3.12.6 Version de GDAL/OGR 3.9.2 Version de Proj 9.4.0 Version de la base de données du registre EPSG v11.004 (2024-02-24) Version de GEOS 3.12.2-CAPI-1.18.2 Version de SQLite 3.45.1 Version de PDAL 2.6.3 Version du client PostgreSQL 16.2 Version de SpatiaLite 5.1.0 Version de QWT 6.2.0 Version de QScintilla2 2.14.1 Version de l'OS Windows 10 Version 2009

Extensions Python actives
GroupStats
2.2.7
mapswipetool_plugin
1.3
networks
2.7.19
OpenTopography-DEM-Downloader
2.0
qfieldsync
v4.9.1
quick_map_services
0.19.34
db_manager
0.1.20
grassprovider
2.12.99
processing
2.12.99

Supported QGIS version

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

New profile

• I tried with a new QGIS profile

Additional context

No response

[agiudiceandrea]

@Ipickedausername, thanks for reporting.

Are you sure the layer has the right CRS assigned? It looks like the features are located in the middle of the Atlantic Ocean and have a maximum dimension of few millimetres.

Does the issue also occur if you select the polygon feature before trying to add a ring in it?

The provided folder contains 4 layers and a project file and the provided project contains 3 layers. May you please describe which layer should be edited and how exactly in order to replicate the issue?

[Ipickedausername]

Hello,

Yes, I simply created a project and specified the CRS before doing the tests. I didn't add a base map, so I didn't notice it was in the middle of the ocean.

I adjusted the location of the polygons, somewhere in France, where Lambert93 apply. I was able to reproduce this issue.

However, I wasn't able to reproduce the issue when the polygon is selected !
Same error if 2 polygons are selected and the ring is contained in one of them.

So, it seems that, if the polygon isn't selected, QGIS cannot always detect where the ring is located?

The layer I used to do these tests is called Layer1.

[agiudiceandrea]

It looks like the issue didn't occur using QGIS <= 3.26 while it does occur using QGIS >= 3.28. The regression may be related to #50447.
I'll propose a fix.