gdal vector pipeline: warn if no features were written

[dbaston]

Feature description

If the GML driver is not available, the following command happily writes an empty file with no warning:

gdal vector pipeline \
            ! read WFS:"https://data.geopf.fr/wfs/ows?version=2.0.0&typename=ADMINEXPRESS-COG.2017:commune" \
            ! filter --where "insee_com='90065'" \
            ! write --output-layer=commune commune.fgb

Additional context

No response

[jratike80]

Was it totally empty, or with a schema but without any features? The latter case would be similar to the result from

ogr2ogr empty.fgb input.gpkg -sql "select * from input where 1=2"

[dbaston]

Yes, I get a schema with no features.

[rouault]

I'm wondering if we should warn. There are probably use cases where an empty layer is expected. (and I'm aware of some GDAL (API) users fail on GDAL warnings, although I wouldn't recommend doing that)