geometry collections being skipped in v0.8.x

[springmeyer]

Special handling to encode each component part of a geometry collection was added here: https://github.com/mapbox/mapnik-vector-tile/blob/887e82a1011f02ad9ef0aa756018b03e6665c81d/src/vector_tile_processor.ipp#L799-L812 to solve #98.

However rendering osm data I encountered a situation where geometry collections still hit the encoder_visitor (or maybe it was the simplify_visitor?). Either way, this is unexpected. I would expect that if this check is working then no geometry collections would ever be encountered in the visitors. Not unless boost::geometry::simplify could create collections?

Anyway, this ticket captures the reason I disabled collections hastily in https://github.com/mapbox/mapnik-vector-tile/commit/dee4e3a332e8c5ee23952439b787a02057a90ce3

The next action is:

• testcase to try to replicate a collection being passed into handle_geometry
• if there are actually valid situations where a collection could be passed to handle_geometry (which I doubt) then we should handle them somehow instead of throwing. Perhaps we could track the original geometry type: if it was a polygon and then a collection of polygon+point was encountered we could encode the polygon and skip the point. But really I can't see how collections should even get into handle_geometry in the first place

[flippmoke]

A geometry collection could contain a geometry collection, therefore the logic in the check is not sufficient. I will write something to address this.

[morganherlocker]

I ran into this recently as well.

[yhahn]

:weary: