Use `cli` to give detailed, friendly error messages

[capnrefsmmat]

There are a few functions that call stop() to signal invalid inputs or other user errors. We should use cli_abort() for these. It allows you to give detail on the types of arguments and what was expected, in a much friendlier way than just pasting together a message in stop().

Here are a couple examples from a package of mine:

  if (!inherits(population, "population")) {
    cli_abort(c("{.arg population} argument must be a population defined with {.fn population}",
                "i" = "Received {.type {population}} instead"))
  }

    cli_abort(
      c("Diagnostic function {.arg fn} must return a data frame or tibble",
        "x" = "{.arg fn} returned a result of class {.cls {class(x)}}"),
      class = "regressinator_diagnostic_class",
      call = caller_env()
    )

These get pretty-printed with colored formatting, and the markup like {.cls} produces nice formatting. For instance, here's what you get from the second example:

Error in `sampling_distribution()`:
! diagnostic function `fn` must return a data frame or tibble
✖ `fn` returned a result of class <character>
Run `rlang::last_trace()` to see where the error occurred.