It is possible to make piechart style in Geoserver WMS using XML SLD. For this adding chart extension is required.
Now, is it possible to make such piechart with YSLD ?
Additional info:
My colleague tried it with YSLD with the following result: 
The size: ${diameter} seems to be understood correctly by GeoServer as the size of grey squares vary.
Now to the problem: the piechart is rendered only as grey square as if the piechart plugin is not installed. Meanwhile I confirm that the piechart plugin is in place and other SLD style (not YSLD) specifying piecharts are rendered as expected.
How to fix this?
My playground:
- GeoServer 2.14.3 (with chart extension)
- Apache Tomcat 8.5.32 Server
- Windows 10 Pro 64-bit on Xeon E5-1660 3GHz, 32GB memory
- PostgreSQL 9.6.11, PostGIS 2.5