Allow using functions that return NULL in aes()

[yutannihilation]

It's common practice to wrap unsafe calculations with tryCatch() and return NULL, which allows us to use the result when available and skip when unavailable. But, currently, ggplot2 doesn't accept this in aes():

library(ggplot2)

df <- data.frame(x = 1:10, y = 1:10)
wrap <- function(...) tryCatch(..., error = function(e) NULL)

ggplot(df, aes(x, y, colour = wrap(no_such_column))) +
  geom_point()
#> Error: Aesthetics must be either length 1 or the same as the data (10): colour

This is because Layer$compute_aesthetics() removes NULL aes here BEFORE evaluation:

ggplot2/R/layer.r

Lines 221 to 223 in f5a88a7

	aesthetics <- compact(aesthetics)
	evaled <- lapply(aesthetics, rlang::eval_tidy, data = data)

Considering the following facts, I think it's safe to move compact() after evaluation

• ggplot2::compact() removes only NULL
• NULL will be still NULL after evaluation

[hadley]

I think you can simplify this to just function() NULL

[yutannihilation]

Agreed.

[hadley]

Can you please add a bullet to NEWS? It should briefly describe the change and end with (@yourname, #issuenumber).

[yutannihilation]

Thanks! I tend to forget about NEWS bullets, sorry.

[lock]

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