after_scale() in the initial ggplot() call

[mikmart]

Consider the after_scale() example from ?aes_eval:

library(ggplot2) # tidyverse/ggplot2@a132727

ggplot(mpg, aes(class, hwy)) +
  geom_boxplot(aes(colour = class, fill = after_scale(alpha(colour, 0.4))))

Moving the colour and fill specification form the geom to the initial ggplot() call causes the fill to not be mapped at all:

ggplot(mpg, aes(class, hwy, colour = class, fill = after_scale(alpha(colour, 0.4)))) +
  geom_boxplot()

[yutannihilation]

Thanks, this seems because Layer$compute_geom_2() refers only to the layer's mapping and ignores plot$mapping.

ggplot2/R/layer.r

Lines 356 to 364 in a132727

	compute_geom_2 = function(self, data) {
	# Combine aesthetics, defaults, & params
	if (empty(data)) return(data)
	aesthetics <- self$mapping
	modifiers <- aesthetics[is_scaled_aes(aesthetics) | is_staged_aes(aesthetics)]
	self$geom$use_defaults(data, self$aes_params, modifiers)
	},

I think compute_geom_2() needs to take plot as we do with map_statistics().

ggplot2/R/plot-build.r

Line 73 in a132727

data <- by_layer(function(l, d) l$map_statistic(d, plot))