`scale_*_reverse()` should not be limited to continuous data

[adisidev]

scale_*_reverse() should allow discrete data that we have comparators for (or anything we can reorder using desc). For instance, strings can be ordered alphabetically. scale_*_reverse() would be the the most intuitive choice one would think about when trying to reverse their axes. However, running it with discrete data yields the following error:

baz <- tibble(foo = c(0, 1, 2), bar = c("b", "a", "c"))
ggplot(baz, aes(x = foo, y = bar)) +
  geom_point() +
  scale_y_reverse()

Error in -x : invalid argument to unary operator

Replacing the last line with scale_y_reverse(NULL) also returns the same error.

If scale_*_reverse() cannot be changed in such a manner as to be able to accept discrete data, perhaps a simple function scale_*_reverse_discrete() may be helpful, rather than the current workaround below:

ggplot(baz, aes(x = foo, y = bar)) +
  geom_point() +
  scale_y_discrete(limits = rev)

(inspired by https://stackoverflow.com/questions/28391850/reverse-order-of-discrete-y-axis-in-ggplot2)

EDIT: Fixed formatting, removed extraneous NULL

[hadley]

Reprex:

library(ggplot2)

baz <- tibble::tibble(foo = c(0, 1, 2), bar = c("b", "a", "c"))
ggplot(baz, aes(x = foo, y = bar)) +
  geom_point() +
  scale_y_reverse()
#> Error in -x: invalid argument to unary operator

^{Created on 2022-04-19 by the reprex package (v2.0.1)}

This could at least be a more informative error

[yutannihilation]

A kind of related: #4014