`margin_part` seems not to work in `legend.box.margin` yet

[Breeze-Hu]

Hi, Teun!

I was trying to adjust the distance of the legend part from the left border of the plot when I accidentally discovered that margin_part() seems not to work like margin() now:

library(ggplot2)

ggplot(iris, aes(Species, Sepal.Length, color = Species)) +
  geom_boxplot() +
  theme(legend.position = 'bottom',
        legend.box.background = element_rect(color = 'red'),
        legend.justification = c(0.3,1),
        legend.box.margin  = margin(t = 0, r = 0, b=0, l = 30, unit = 'pt'))

• The left line of the legend box also does not match the initial width. (This is of course not the core problem)

But trying a partial adjustment to use margin_part() instead of margin() reported an error:

ggplot(iris, aes(Species, Sepal.Length, color = Species)) +
  geom_boxplot() +
  theme(legend.position = 'bottom',
        legend.box.background = element_rect(color = 'red'),
        legend.justification = 'left',
        legend.box.margin  = margin_part(t = NA, r = NA, b=NA, l = 30, unit = 'pt'))
#> Error in `plot_theme()`:
#> ! Can't merge the `legend.box.margin` theme element.
#> Caused by error in `as.unit()`:
#> ! object is not coercible to a unit

^{Created on 2025-06-28 with reprex v2.1.1}

As I know you are busy with the issue of reverse dependencies for the next version update, THANK YOU FOR YOUR WORK!
Hope this doesn't disturb you.

Best wishes,
Hu

[teunbrand]

Thanks for the report! This should definitely not an error. I think this might be because the default value is rel(0) and this cannot be used to fill in the NAs in the merge_element() step.