linetype incorrectly renders in legend when drop=FALSE

[jnolis]

Hi!

When I use scale_linetype_manual to specify line types for different discrete levels, the legend in correctly renders. The dropped linetypes do show up in the legend but their squares are blank. This is using version 3.5.2. Thanks!

library(tidyverse)

df <- tibble(
  x = c(1,2,1,2), 
  y = c(0,1,1,0), 
  group = c("a","a","b","b") |> factor(levels = c("a","b","c"))
)

ggplot(df,aes(x=x,y=y,group=group,linetype=group)) + geom_line()+
  scale_linetype_manual(values=c("a"="solid","b"="dashed","c"="twodash"),drop=FALSE)
  

[teunbrand]

You can use geom_line(show.legend = TRUE) if you want unobserved levels to show up in the legend.

[jnolis]

That did fix it! And upon reflection it seems like it's not linetype specific, it happens with other aesthetics too.

That said, is this the desired behavior? I would expect for any scenario if drop=FALSE then the values should show in the legend just like show.legend=TRUE

[smouksassi]

while this was a breaking change it enabled lot of possibilities not available before:
https://www.tidyverse.org/blog/2024/02/ggplot2-3-5-0-legends/
quote:
the show.legend argument can still be set in an aesthetic-specific way. Setting it to TRUE means ‘always show’, FALSE means ‘never show’ and NA means ‘show if found’.
it took me a bi to adjust especially when I patchwork several plots that I want to have the same shared legend when some plots did not have a level.
Samer

[teunbrand]

This issue has been discussed elsewhere before and we like to keep the current intentional behaviour.