[QGIS-Developer] QGIS3 Plugin debugging help

[Chris Crook]

Hi All

I am looking for suggestions on how to debug a plugin that is crashing QGIS3

I am trying to port the contour plugin to QGIS3.  The port is largely done but there is one outstanding issue that causes QGIS to die.

The plugin uses the python matplotlib library to do the contouring.  It has two modes of operating.  If the source data is gridded it will use the plt.contour function, and this is working as it should.  If the data is not gridded it uses the plt.tricontour function, which builds a triangulation and then uses that to do the contouring.   When the plugin calls this function it crashes QGIS.  I've extracted the data used in the function call from QGIS and run the tricontour function from a simple python program and it runs without error.  So something in the QGIS plugin environment is causing this to fail.

Can you suggest approaches to debugging this, or getting more information about where it is failing (or for that matter fixing it).   The code in question is in

https://github.com/ccrook/QGIS-Contour-Plugin/blob/qgis3_wip/contour/contour.py#L846

I am running on ubuntu 16.04 using the ubuntugis-nightly distribution.  Details are


QGIS version
2.99.0-Master
QGIS code revision
bcbc46b
Compiled against Qt
5.5.1
Running against Qt
5.5.1
Compiled against GDAL/OGR
2.2.2
Running against GDAL/OGR
2.2.2
Compiled against GEOS
3.5.1-CAPI-1.9.1
Running against GEOS
3.5.1-CAPI-1.9.1 r4246
PostgreSQL Client Version
9.5.2
SpatiaLite Version
4.3.0a
QWT Version
6.1.2
PROJ.4 Version
492
QScintilla2 Version
2.9.1
This copy of QGIS writes debugging output.

Matplotlib version is 1.5.1


Thanks for any suggestions - I'm feeling a bit stuck with this one :-(

Chris

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