I'd rather replace with this something simple, that I know works:

```R
sys.source2 <- function(file, envir = parent.frame()) {
  stopifnot(file.exists(file))
  stopifnot(is.environment(envir))
  
  lines <- readLines(file, warn = FALSE)
  srcfile <- srcfilecopy(file, lines, file.info(file)[1, "mtime"],
    isFile = TRUE)
  exprs <- parse(text = lines, n = -1, srcfile = srcfile)
  
  n <- length(exprs)
  if (n == 0L) return(invisible())
  
  eval(exprs, envir)
  invisible()
}
```