Legend that shows points vs lines in ggplot2

I am trying to generate a legend in ggplot that shows points with a different name than lines. I need that legend to show up separately from the legend that is showing color, shape, and linetype.

I originally had code similar to this smaller example, which works. Basically, I artificially set a size aesthetic for both the points and lines, then override the legend to only show one or the other. From what I can tell, this is how people have been adding regression lines to their plots. However, using the size aesthetic for lines was deprecated in ggplot2 version 3.4.0. It still works, but I think the behavior has changed slightly.

# Use iris dataframe as example and create new column for horizontal lines
data <- iris %>%
  group_by(Species) %>%
  mutate(AvgLength = mean(Petal.Length))

ggplot(data) +
  geom_point(aes(x = Petal.Width, y = Petal.Length, color = Species, shape = Species, size = "Samples")) +
  geom_hline(aes(yintercept = AvgLength, color = Species, linetype = Species, size = "Average")) +
  # Set manual size to get normal points and linewidths
  scale_size_manual(values = c("Average" = .5, "Samples" = 1.5)) +
  # Override the size legend to show only a line for the first entry and only a point for the second
  guides(size = guide_legend(override.aes = list(linetype = c(1,0), shape = c(NA, 16)), title = ""))

Plot with desired legends

In my actual application, the line name comes alphabetically after the points name (but should show up first in the legend), which breaks the legend, as shown here. I think the order from the size_scale was respected in the legend when I first wrote the code (pre 3.4.0), but I'm not sure.

ggplot(data) +
  geom_point(aes(x = Petal.Width, y = Petal.Length, color = Species, shape = Species, size = "Aa")) +
  geom_hline(aes(yintercept = AvgLength, color = Species, linetype = Species, size = "Average")) +
  scale_size_manual(values = c("Average" = .5, "Aa" = 1.5)) +
  guides(size = guide_legend(override.aes = list(linetype = c(1,0), shape = c(NA, 16)), title = ""))

Plot with legend messed up by name order

I would like to do things right with the new version of ggplot, and not use the size aesthetic, but I'm not sure how to have both points and lines on the same legend with a different aesthetic since I'm already using color for something else. The closest I can get is showing them as two separate legends like below, then somehow manually changing the spacing. However, this solution isn't great if you have to apply it to multiple types of plots where the legends are being shown in different places, and I'm not sure how to manually fix the spacing between the size and linewidth legends, while leaving the other legend alone.

ggplot(data) +
  geom_point(aes(x = Petal.Width, y = Petal.Length, color = Species, shape = Species, size = "Aa")) +
  geom_hline(aes(yintercept = AvgLength, color = Species, linetype = Species, linewidth = "Average")) +
  scale_size_manual(values = c("Average" = .5, "Aa" = 1.5)) +
  scale_linewidth_manual(values = c("Average" = .5)) +
  guides(size = guide_legend(title = "", order = 1),
        linewidth = guide_legend(title = "", order = 2))

Plot that doesn't use the size aesthetic for lines, but the legends look weird

I'm aware that ggplot generally doesn't play well with manual legend specification because of how you should be setting up your plots and dataframes. However, I think in this application, it would be hard to set up the dataframe differently. Does anyone have a clean solution for this problem?

As we now have to deal with two aesthetics we have to ensure that the legends get merged by "duplicating" the specification of the scale, i.e. set a value for both categories in both scales and also set the limits to actually include both categories in each legend. Doing so the size and lindwidth legends get merged, via the limits you could also set the order of the categories in the legend and finally we can use override.aes to polish the legend, i.e. get rid of the shape for the "line" category and the linetype for the "point" category.

library(ggplot2)

ggplot(data) +
  geom_point(aes(x = Petal.Width, y = Petal.Length, color = Species, shape = Species, size = "Aa")) +
  geom_hline(aes(yintercept = AvgLength, color = Species, linetype = Species, linewidth = "Average")) +
  scale_size_manual(values = c("Average" = .5, "Aa" = 1.5), limits = c("Average", "Aa")) +
  scale_linewidth_manual(values = c("Average" = .5, "Aa" = 1.5), limits = c("Average", "Aa")) +
  labs(size = NULL, linewidth = NULL) +
  guides(
    size = guide_legend(
      override.aes = list(linetype = c("solid", "blank"), shape = c(NA, 16))
    )
  )