Legend title not shown in horizontal orientation

[richierocks]

The legend title is not shown for legends in horizontal orientation.

Here's a line plot with a legend.

library(ggplot2)
library(plotly)

plt <- ggplot(Orange, aes(age, circumference, group = Tree, color = Tree)) + 
  geom_line()

The plotly version with a vertical legend correctly displays the title.

ggplotly(plt)

If I change to horizontal orientation, the title is no longer present

ggplotly(plt) %>% 
  layout(
    legend = list(
      orientation = "h"
    )
  )

Notice that the word "Tree" is not present in this image.

This is a low priority bug since there is a workaround: you can manually specify the legend title.

ggplotly(plt) %>% 
  layout(
    legend = list(
      orientation = "h", 
      title = list(text = "Tree")
    )
  )

[cpsievert]

Duplicate of #1049 (there's a WIP #1697)