Frustrating stripping of newlines and whitespace in `warning_cnd()` and `error_cnd()`

[DavisVaughan]

Consider the following lifecycle message

warn_case_when_scalar_lhs_vector_rhs <- function(
  user_env,
  error_call
) {
  details <- paste(
    sep = "\n",
    "Please use a series of simpler if statements with early returns instead.",
    "# Previously",
    "case_when(scalar_lhs1 ~ rhs1, scalar_lhs2 ~ rhs2)",
    "# Now",
    "if (scalar_lhs1) {",
    "  return(rhs1)",
    "}",
    "",
    "if (scalar_lhs2) {",
    "  return(rhs2)",
    "}"
  )

  lifecycle::deprecate_soft(
    when = "1.2.0",
    what = I("Using `case_when()` with scalar LHS and vector RHS"),
    details = details
  )
}

This shows

Warning message:
Using `case_when()` with scalar LHS and vector RHS was deprecated in <NA> 1.2.0.
ℹ Please use a series of simpler if statements with early returns instead. # Previously
  case_when(scalar_lhs1 ~ rhs1, scalar_lhs2 ~ rhs2) # Now if (scalar_lhs1) { return(rhs1) }

if (scalar_lhs2) { return(rhs2) }

I seem to often be frustrated by rlang/cli stripping out purposeful leading whitespace and newlines from my error messages.

It seems like this rougly boils down to these two annoyances

# With a single string, newlines and whitespace are stripped
rlang::warning_cnd(message = "a\n      b", use_cli_format = TRUE)
#> <warning/rlang_warning>
#> Warning:
#> a b

rlang::warning_cnd(message = "a\n      b", use_cli_format = FALSE)
#> <warning/rlang_warning>
#> Warning:
#> a
#>       b

# With multiple strings, whitespace is stripped
rlang::warning_cnd(message = c("a", "    b"), use_cli_format = TRUE)
#> <warning/rlang_warning>
#> Warning:
#> a
#> b

rlang::warning_cnd(message = c("a", "    b"), use_cli_format = FALSE)
#> <warning/rlang_warning>
#> Warning:
#> a
#>     b

It also seems to have something to do with the fact that dplyr calls local_use_cli() for itself on load, but I don't think that is the real problem.

The main issue is that I don't know how to write this multiline error message

[DavisVaughan]

Actually this might have to do with lifecycle itself setting local_use_cli() internally

https://github.com/r-lib/lifecycle/blob/2a852fee7c4f873b865ffe9553150fefc1f1becf/R/lifecycle-package.R#L16

Because that forces cli usage in warning_cnd() and friends, which seems to be what is preventing me from making these messages? I'm not sure, it's confusing.

[DavisVaughan]

Current solution is to swap all spaces and newlines with some special unicode characters that cli ignores

# Suppress cli wrapping https://cli.r-lib.org/reference/inline-markup.html#wrapping
no_cli_wrapping <- function(x) {
  x <- gsub(" ", "\u00a0", x, fixed = TRUE)
  x <- gsub("\n", "\f", x, fixed = TRUE)
  x
}

[lionel-]

I think this is a cli issue, there should be a way to turn off wrapping, for instance inside backticked chunks.