Make sure that expressions are reencoded as expressions when collapsed

[thomasp85]

Fix #4084

There is one "issue" in that parsing is either, or. Right now it will re-add parsing if any label is an expression which could potentially lead to errors if there is a mix of expressions and not (I'm not sure if that is possible) and the non-expressions cannot be parsed...

Alternatively we could only do this if all labels are expressions...

library("ggplot2")

dat <- data.frame(x = 1, y = 1, a = "a", b = 1)

ggplot(dat, aes(x, y)) +
  geom_point() +
  facet_grid(
    ~ a + b,
    labeller = labeller(
      a = c("a" = "a^2"),
      .default = label_parsed,
      .multi_line = FALSE
    )
  )

^{Created on 2021-04-14 by the reprex package (v2.0.0)}

[thomasp85]

I decided to switch to all() instead of any() as it seems the safest

[karawoo]

This seems good to me. It is possible to have a mix of expressions and non-expressions (below). But at that point the label is the combined text of both the labels, so if they aren't all expressions then I think it's a reasonable limitation to not try to parse them.

library("ggplot2")

dat <- data.frame(
  x = 1,
  y = 1,
  fruit = "apple",
  veg = "carrot",
  stringsAsFactors = TRUE
)

ggplot(dat, aes(x, y)) +
  geom_point() +
  facet_grid(
    ~ fruit + veg,
    labeller = labeller(
      fruit = c("apple" = "a^2"),
      veg = label_both,
      .default = label_parsed,
      .multi_line = FALSE
    )
  )

^{Created on 2021-04-14 by the reprex package (v0.3.0.9001)}

[thomasp85]

yeah, it is not possible to mix it without a very big rewrite of the strip rendering system which I don't think is warranted at this point