error_arg() and error_call() should have better fall backs when called directly

[hadley]

library(rlang)

foo <- function(x, arg = caller_arg(x), call = caller_env()) {
  cli::cli_abort("Error {.arg {x}}", call = call)
}
foo(123)
#> Error:
#> ! Error `123`

^{Created on 2023-11-09 with reprex v2.0.2.9000}

Ideally this would be

#> Error: foo()
#> ! Error `x`

[lionel-]

Unfortunately I don't think we can do better here.

[lionel-]

Though we could detect calls at top-level. The behaviour would then differ when called directly vs in a browser or in testthat or markdown.

[hadley]

The thing that makes me think we could do better is that it's the same appearance at the top level and in snapshot:

Code
  foo(123)
Condition
  Error:
  ! Error `123`