geom_mark_*() errors in webR when description is missing

[z3tt]

Hi Thomas 👋

Hope you’re well!

We’ve run into something odd with geom_mark_*() and wanted to check whether this is expected behavior or a small edge case. And if there is anythoing we are missing and potential ways to fix it (either from oru or your side).

In webR-based environments, which we’re using in-browser sandboxes in our uncharted course, geom_mark_*() (e.g. `geom_mark_circle()) throws:

Error: Problem while converting geom to grob.

This happens whenever a description is not porivded. What’s surprising is that the error completely disappears as soon as any character string is provided for the description.

---

🔁 Minimal example

This fails in webR:

library(ggplot2)
library(ggforce)

ggplot(
    data = penguins,
    aes(x = flipper_len, y = body_mass, fill = species)
) +
    geom_mark_ellipse(aes(label = species)) +
    geom_point(shape = 21, size = 2)

This works:

library(ggplot2)
library(ggforce)

ggplot(
    data = penguins,
    aes(x = flipper_len, y = body_mass, fill = species)
) +
    geom_mark_ellipse(aes(label = species, description = "")) + # empty quotes for description make it work
    geom_point(shape = 21, size = 2)

---

Our hypothesis after doing some research: the grob tree constructed by geom_mark_*() is incomplete when description is missing, and webR’s graphics device is stricter about validating grobs. In a full desktop R session, this seems to slip through unnoticed, but in webR it fails hard.

If that's the reason:
Would it be possible for geom_mark_*() to return a complete grob structure, even when description is not supplied, so it behaves consistently across devices?

Thanks a lot for ggforce and all your other packages 🙌

[z3tt]

After some more investigation, I am not fully convinced anymore that it's (purely?) related to that alone. We are still checking what's going on as we have been able to make it work with some settings, but it fails with some others. Once we know more, I'll update this comment or delete the issue.

[z3tt]

It turns out to be an old bug; newer versions of webR do not exhibit this behavior. Going to close this issue.