Some GDAL processing tools raise exceptions if active layer is unavailable

[kannes]

What is the bug or the crash?

Some GDAL processing tools raise exceptions if active layer is unavailable

Steps to reproduce the issue

Set up an unavailable layer, e.g. by moving a referenced file or by breaking WFS access like this:

1. Go to Options -> Network
2. Enable Use Proxy for Web Access
3. Choose HttpProxy or something else where you can specify a proxy
4. Set the host to localhost and the port to a port where you do not have a proxy running (e.g. 34567 probably)
5. Add a WFS layer to your QGIS project, e.g. ms:inv80_lgeomorph from http://maps.zh.ch/wfs/FnsNSWFS (random result from web search)

At this stage QGIS should show a warning sign next to the layer in the layer tree. If so, continue:

1. Try to open a GDAL processing tool like gdal:buffervectors, gdal:dissolve or gdal:ogrinfo (other vector tools did not raise this exception for me).

You will get a yellow "Python error" message and a stack trace like this:

2023-02-21T11:24:04     WARNING    Traceback (most recent call last):
              File "/usr/share/qgis/python/plugins/processing/ProcessingPlugin.py", line 387, in executeAlgorithm
              dlg = alg.createCustomParametersWidget(parent)
              File "/usr/share/qgis/python/plugins/processing/algs/gdal/GdalAlgorithm.py", line 64, in createCustomParametersWidget
              return GdalAlgorithmDialog(self, parent=parent)
              File "/usr/share/qgis/python/plugins/processing/algs/gdal/GdalAlgorithmDialog.py", line 56, in __init__
              self.mainWidget().parametersHaveChanged()
              File "/usr/share/qgis/python/plugins/processing/algs/gdal/GdalAlgorithmDialog.py", line 143, in parametersHaveChanged
              commands = self.algorithm().getConsoleCommands(parameters, context, feedback, executing=False)
              File "/usr/share/qgis/python/plugins/processing/algs/gdal/Buffer.py", line 103, in getConsoleCommands
              raise QgsProcessingException(self.invalidSourceError(parameters, self.INPUT))
             _core.QgsProcessingException: Could not load source layer for INPUT: Geomorphologische_Objekte_Inv__80__faa3c9a6_2825_40d3_ae75_8eec4e96bc92 not found

The tool should fail later or differently, with a user-friendly message, not a traceback. Other tools seem to simply not pre-populate their input comboboxes with this layer.

Versions

QGIS-Version	3.28.3-Firenze	QGIS-Codeversion	c12bcb2
Qt-Version	5.15.3
Python-Version	3.10.6
GDAL-Version	3.4.1
PROJ-Version	8.2.1
EPSG-Registraturdatenbankversion	v10.041 (2021-12-03)
GEOS-Version	3.10.2-CAPI-1.16.0
SQLite-Version	3.37.2
PDAL-Version	2.3.0
PostgreSQL-Client-Version	unknown
SpatiaLite-Version	5.0.1
QWT-Version	6.1.4
QScintilla2-Version	2.11.6
BS-Version	Ubuntu 22.04.1 LTS
Aktive Python-Erweiterungen
Qgis2threejs	2.7.1
QuickOSM	2.1.1
processing	2.12.99
sagaprovider	2.12.99
grassprovider	2.12.99
MetaSearch	0.3.6
db_manager	0.1.20

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

I did not test raster tools similarly.

[agiudiceandrea]

It seems to me the issue doesn't occur on my Windows system with QGIS 3.28.3:

gdalprocessing.mp4

[kannes]

Thanks a lot, @nyalldawson!