Add extra validation when .by is supplied and a group data frame (r…

…epeat the error message from mutate() for a better stack trace.

R/fill.R

@@ -115,6 +115,11 @@ fill.data.frame <- function(data, ..., .direction = c("down", "up", "downup", "u
   }
 
   if (dplyr::is_grouped_df(data)) {
+    if (length(by) > 0) {
+      cli::cli_abort(c(
+        "Can't supply {.arg .by} when {.arg data} is a grouped data frame."
+      ))
+    }
     dplyr::mutate(data, dplyr::across(any_of(vars), .fns = fn))
   } else {
     dplyr::mutate(data, dplyr::across(any_of(vars), .fns = fn), .by = all_of(by))

tests/testthat/_snaps/fill.md

@@ -14,4 +14,9 @@
       Error in `fill()`:
       ! Can't select columns that don't exist.
       x Column `z` doesn't exist.
+    Code
+      gr_df %>% fill(y, .by = x)
+    Condition
+      Error in `fill()`:
+      ! Can't supply `.by` when `data` is a grouped data frame.
 

tests/testthat/test-fill.R

@@ -134,7 +134,9 @@ test_that("validates its inputs", {
 
 test_that("fill works with .by", {
   df <- tibble(x = c(1, 1, 2), y = c(1, NA, NA))
+  gr_df <- dplyr::group_by(df, x)
   expect_snapshot(error = TRUE, {
     df %>% fill(y, .by = z)
+    gr_df %>% fill(y, .by = x)
   })
 })