ggplotly() is unable to merge legend entries across layers

Thanks for an amazing package! The mapping between plotly and ggplot is particularly impressive and very powerful!

However, ggplotly fails to reproduce the appropriate legends generated by ggplot in non-trivial facet_wrap cases. After discussion on stackoverflow some of this behavior appears to be a bug.

Consider the following minimal reprex:

library(plotly)
library(ggplot2)

p <- mpg %>% 
  ggplot(aes(year)) +
  geom_ribbon(aes(ymin=cty, ymax=hwy, fill = manufacturer), alpha=0.2) + 
  geom_line(aes(y = hwy, col=manufacturer))  +
  facet_wrap(~class)
p
plotly::ggplotly(p)

Note that (a) we get too many plotly legend entries, duplicating the legend for each facet, due to legendgroup not being correctly handled. Also note (b) the legends we do and don't get depend on the order (do we do geom_ribbon first or geom_line first). The bug does not appear if we have only one geom, and the missing legends continue as we add more geoms.

Perhaps not related -- but the interactive zoom options in faceted plots are not entirely intuitive either, i.e. it's not possible to zoom the whole window on a single facet plot. (Perhaps the take home is that it might be better to render facet plots as more independent objects in plotly)?

Inizia con il reprex minimo di ggplotly() usando geom_ribbon, geom_line e facet_wrap(~class), quindi esamina come viene gestito legendgroup tra layer e facet. Confronta le legende convertite con le risultati attesi delle legende di ggplot2; il lavoro è completato quando non ci sono voci duplicate o mancanti indipendentemente dall’ordine dei geom, preservando il comportamento dei facet.