Altair: invisible symbol in legend for mark_trail

[YuliaGazizova]

Hey guys!
Thank you for Altair.
Recently, I met a small but quite annoying bug: with mark_trail graph, symbols in a legend are not visible. Not only line thickness but all symbols in a legend. You can see an example of such behavior even on the Altair page https://altair-viz.github.io/gallery/trail_marker.html.
Another example I attached as a print screen:

1. mark_trail graph. Symbols in the legend are not visible
2. mark_line graph with the same data. Symbols in the legend are visible
   
   
   Is it because I am stupid or it is a bug?
   Yulia

[jakevdp]

This is a bug in Vega-Lite that was recently fixed: https://github.com/vega/vega-lite/issues/5879

The fix should make it into the next Altair release.

[YuliaGazizova]

Ok.
Thank you!

[kaisengit]

I've just updated to altair 4.1.0 and the bug is still there for me. Should it not be fixed now?

[jakevdp]

It should be fixed; for example it works correctly in the documentation now: https://altair-viz.github.io/gallery/trail_marker.html

How are you rendering your Altair charts?

[kaisengit]

Ops, I am sorry, it is indeed fixed. Beforehand I was using a square mark which also made big squares in the legend. The trail mark is just using very thin trails indeed for the legend. And that combined with the colors I chose made them very hard to see but they are there now. So this issue can probably be closed.

[jakevdp]

Great, thanks for checking!