Bug report #20661
QgsPoint.clone() not fully reliable? It's original QgsFeature may get corrupted?
|Category:||Python bindings / sipify|
|Affected QGIS version:||3.5(master)||Regression?:||Yes|
|Operating System:||Windows 7 64 bits||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:||up/downstream|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||28481|
We have stumbled upon an strange problem and reproducible problem. We attach a plugin to reproduce it.The problem arises in this circumstances:
- We have a layer. We iterate over all its features, then over all their geometries, then all of their nodes (QgsPoints). To reproduce the problem, we use a layer with only a single polygon.
- For each node, we create a new QgsFeature (in memory), and we assign it a new geometry initialized with a clone of the node (QgsPoint)
- The original layer is not modified in any way, nor its features.
- We then repeat the above steps. We may repeat it successfully but only for a limited and variable number of iterations.
- Eventually, the process will break with an unexpected exception.
- More precisely, the exception raises because eventually we get a PolygonGeometry QgsGeometry (as expected), but its actual geometry (geom.constGet()) is reported as a QgsPoint. Debugging, it looks as "<QgsPoint: MultiPolygon (...)>", as shown in the attached screenshots.
How to reproduce it
We have prepared a plugin to easily reproduce the issue. We have attached as 'issuePlugin.zip' to this bug report.
You only need to install it in QGis. Then, a toolbar with a spider will appear (see above screenshots). You only need to click this icon. A dialog will open, showing how the test iterates until the unexpected exception is raised.
We have tested it in Qgis 3.5 MASTER and 3.4.1.
#2 Updated by Martin Dobias 11 months ago
I can replicate on linux too.
Simplified code to reproduce the issue:
import sip for i in range(50): geom = QgsGeometry.fromWkt("MULTIPOLYGON(((1 1, 1 2, 2 2, 2 1, 1 1)))") geomV2 = geom.constGet() if isinstance(geomV2, QgsPoint): print("WHAT??????!!!!! " + hex(sip.unwrapinstance(geomV2))) pt = QgsGeometry.fromWkt("POINT( 3 4 )") pt_g = pt.constGet() pt_clone = pt_g.clone() pt_x = QgsGeometry(pt_clone) print("new pt " + hex(sip.unwrapinstance(pt_clone))) print("-----")