A QgsProcessingParameter with custom WidgetWrapper can't be connected correctly in the Model Designer

[janzandr]

What is the bug or the crash?

I want to implement a QgsProcessingAlgorithm with a QgsProcessingParameterFile that has a custom WidgetWrapper.

Here is a minimal example:

from processing.gui.wrappers import WidgetWrapper
from qgis._core import QgsProcessingParameterFile, QgsProcessingAlgorithm
from qgis._gui import QgsFileWidget


class MyAlgorithm(QgsProcessingAlgorithm):

    def displayName(self):
        return 'My Algorithm'

    def name(self):
        return 'MyAlgorithm'

    def shortDescription(self):
        return 'dummy'

    def group(self):
        return 'Debugging'

    def createInstance(self):
        return type(self)()

    def initAlgorithm(self, configuration):

        # add a normal parameter
        self.addParameter(QgsProcessingParameterFile('file1', 'Normal File'))

        # add a parameter with custom widget
        param = QgsProcessingParameterFile('file2', 'Custom File')
        param.setMetadata({'widget_wrapper': {'class': MyWidgetWrapper}})
        self.addParameter(param)

    def processAlgorithm(self, parameters, context, feedback):
        return {}


class MyWidgetWrapper(WidgetWrapper):
    widget: QgsFileWidget

    def createWidget(self):
        return QgsFileWidget()

    def setValue(self, value):
        self.widget.setFilePath(value)

    def value(self):
        return self.widget.filePath()

Executing the algorithm in the Processing Toolbox works fine.

Using the algorithm in the Model Designer is not working as expected:

The menu-button for correctly connecting previous outputs is missing:

This makes it impossible to actually use the algorithm inside a model.

Steps to reproduce the issue

1. Add the algorithm from above to a processing provider of your choice.
2. Use the algorithm in the Model Designer.
3. See the bug: the "123" menu-button is not shown.

Versions

QGIS version
3.24.2-Tisler
QGIS code revision
13c1a02
Qt version
5.15.3
Python version
3.9.5
GDAL/OGR version
3.4.3
PROJ version
9.0.0
EPSG Registry database version
v10.054 (2022-02-13)
GEOS version
3.10.2-CAPI-1.16.0
SQLite version
3.38.1
PDAL version
2.3.0
PostgreSQL client version
unknown
SpatiaLite version
5.0.1
QWT version
6.1.6
QScintilla2 version
2.13.1
OS version
Windows 10 Version 2009

Active Python plugins
ee_plugin
0.0.4
enmapboxplugin
3.10.0.20220524T082114.TEST
geetimeseriesexplorer
2.0
qgis-maptiler-plugin
3.0.3
timeseriesviewerplugin
1.17.20210312T143004.master
vrtbuilderplugin
0.9.20210222T174536.master
db_manager
0.1.20
grassprovider
2.12.99
MetaSearch
0.3.6
processing
2.12.99
sagaprovider
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

[nyalldawson]

The WidgetWrapper class is deprecated -- this is a wontfix

[janzandr]

Ah ok, thanks.
@nyalldawson can you point me to an alternative, that I suppose to use instead (e.g. an algorithm or documentation).

[janzandr]

Can anybody point me to an example or documentation?
I understand that WidgetWrapper class is deprecated, but how would I implement a custom widget correctly?

[janzandr]

Hi @alexbruy, I understand, that the WidgetWrapper class is deprecated.
But what would be the correct API to use? Any PyQGIS examples available?
Regards, Andreas.