Error for incorrect sxp expand argument does not print list of acceptable values

[samrickman]

Here is a simple example, calling lobstr::sxp() on a numeric vector:

lobstr::sxp(1:5, expand = "numeric")

Output:

Error in `lobstr::sxp()`:
! `expand` must contain only values from
Run `rlang::last_error()` to see where the error occurred.

It looks to me like this is caused by the way the error message is called line 58 of sxp.R.

  opts <- c("character", "altrep", "environment", "call", "bytecode")
  if (any(!expand %in% opts)) {
    abort("`expand` must contain only values from ", paste("'", opts, "'", collapse = ","))
  }

This would work with message() where the first argument is ..., but rlang::abort() expects the first argument to be the message.

After I typed this out, I thought I might as well just fork the repo and amend the error message. I have done this. I will link to this issue in the PR.

I have not added a test as it seemed like overkill but when I run the same code it now produces:

Error in `lobstr::sxp()`:
! `expand` must contain only values from: 'character', 'altrep', 'environment', 'call', 'bytecode'
Run `rlang::last_error()` to see where the error occurred.

This is my first time contributing to a package so I hope it was helpful - if not let me know how it could've been more useful.