do not use column indices as replacement

NEWS.md

@@ -9,6 +9,8 @@ BREAKING CHANGES AND DEPRECATIONS
   - argument `pattern` is deprecated. Use `select` instead.
   - argument `safe` is deprecated. The function now errors when `select` 
     contains unknown column names.
+  - when `replacement` is `NULL`, an error is now thrown (previously, column
+    indices were used as new names).
 
 CHANGES
 

R/data_rename.R

@@ -12,7 +12,6 @@
 #' @param replacement Character vector. Can be one of the following:
 #'   - A character vector that indicates the new names of the columns selected
 #'     in `select`. `select` and `replacement` must be of the same length.
-#'   - `NULL`, in which case columns are numbered in sequential order.
 #'   - A string (i.e. character vector of length 1) with a "glue" styled
 #'     pattern. Currently supported tokens are:
 #'     - `{col}` which will be replaced by the column name, i.e. the
@@ -117,11 +116,6 @@ data_rename <- function(data,
     replacement <- names(select)
   }
 
-  # name columns 1, 2, 3 etc. if no replacement
-  if (is.null(replacement)) {
-    replacement <- paste0(seq_along(select))
-  }
-
   # coerce to character
   replacement <- as.character(replacement)
 

tests/testthat/test-data_rename.R

@@ -53,10 +53,11 @@ test_that("data_rename: replacement not allowed to have NA or empty strings", {
 
 # replacement -------------
 
-test_that("data_rename uses indices when no replacement", {
-  x <- data_rename(test, select = c("Sepal.Length", "Petal.Length"))
-  expect_identical(dim(test), dim(x))
-  expect_named(x, c("1", "Sepal.Width", "2", "Petal.Width", "Species"))
+test_that("data_rename errors when no replacement", {
+  expect_error(
+    data_rename(test, select = c("Sepal.Length", "Petal.Length")),
+    "There are more names in `select` than in `replacement`"
+  )
 })
 
 test_that("data_rename errors when too many names in 'replacement'", {