Preserve the color theme of the parent process?

[wlandau]

Issue

From r-lib/cli#467, cli colors printed from inside callr are not preserved when forwarded to the main process.

Example:

out <- callr::r(
  \() {
     cli::ansi_palette_show()
  },
  show = TRUE
)

Causes

1. cli uses message(), which goes to standard error.
2. The callr child process does not necessarily choose the same number of ANSI colors as the parent process.

Evidence of (2):

cli::num_ansi_colors()
#> [1] 256
callr::r(\() cli::num_ansi_colors())
#> [1] 1

Manual workarounds

1. Redirect stderr to stdout.
2. Inside the callr child process, set the cli.num_colors option to the correct number of colors.

Example:

out <- callr::r(
  \() {
     options(cli.num_colors = 256)
     cli::ansi_palette_show()
  },
  show = TRUE,
  stderr = "2>&1"
)

Request

Is there a way to make cli colors "just work" (TM) using the defaults of both packages? I'm not sure what would need to change, but I do believe that aligning the child process colors with those of the parent would be the most intuitive and convenient default behavior.

[gaborcsardi]

ANSI colors are a feature of the terminal or the IDE. We don't know where the output of a subprocess is going to go, we cannot assume that it is going to the same terminal as the output of the parent process.

So there is no way to change this in practice without producing output with unwanted ANSI sequences that mess up many people's workflows.

[wlandau]

Fair enough, thanks for explaining.