Fixes:
- enum parameters set to "allow multiple" only allow a single
value selection when used in modeler
- optional enum parameters cannot be set to no value when
used outside of modeler
Fixes#20406
Replace with just f[idx]. Calling QgsFeature.attributes()
allocates a list of all attributes, which is inefficient
when only a single attribute value is needed.
Include descriptive text with the specified parameter value
in error, and always check that sources were loaded to avoid
raw Python exceptions when they are not
always add a consistent amount of attributes regardless of the
code paths taken
Some algorithms were adding features to data providers with
different number of attributes vs the layer's fields - this is
not supported and depending on the data provider will have
different (bad) results.
This forces Python code and plugins to become datum transform
aware, and given that upgrading python code is easy (just
add QgsProject.instance() as a new argument to the constructor)
it's relatively painless to force this on PyQGIS users.
Also fix upgrade the easy QgsCoordinateTransform c++ constructors
where the project is available, or where using QgsProject::instance()
is safe to do.
For others, just avoid the deprecated warnings until we can
get access to the correct project instance where the transform
is being constructed.
Like the main Join Attributes by Location algorithm, this algorithm
takes two layers and combines the attributes based on a spatial
criteria.
However this algorithm calculates summaries for the attributes for
all matching features, e.g. calculating the mean/min/max/etc.
The list of fields to summaries, and the summaries to
calculate for those, can be selected.
