Better error for col_factor with non-character levels

Fixes #1140

NEWS.md

@@ -1,5 +1,7 @@
 # readr (development version)
 
+* `col_factor()` now throws a more informative error message if given non-character levels (#1140)
+
 * `write_csv()` now errors if given a matrix column (#1171)
 
 * `write_csv()` now again is able to write data with duplicated column names (#1169)

R/collectors.R

@@ -249,6 +249,9 @@ parse_factor <- function(x, levels = NULL, ordered = FALSE, na = c("", "NA"),
 #' @rdname parse_factor
 #' @export
 col_factor <- function(levels = NULL, ordered = FALSE, include_na = FALSE) {
+  if (!(is.null(levels) || is.character(levels))) {
+    stop(sprintf("`levels` must be `NULL` or a character vector:\n- `levels` is a '%s'", class(levels)), call. = FALSE)
+  }
   collector("factor", levels = levels, ordered = ordered, include_na = include_na)
 }
 

tests/testthat/test-parsing-factors.R

@@ -92,3 +92,7 @@ test_that("Can parse a factor with levels of NA and empty string", {
     as.integer(factor(x, levels = c("NA", "NB", "NC", "")))
   )
 })
+
+test_that("factor levels must be null or a character vector (#1140)", {
+  expect_error(col_factor(levels = 1:10), "must be `NULL` or a character vector")
+})