check the input faceting names

R/facet-.r

@@ -486,6 +486,17 @@ check_layout <- function(x) {
   cli::cli_abort("Facet layout has a bad format. It must contain columns {.col PANEL}, {.col SCALE_X}, and {.col SCALE_Y}")
 }
 
+check_facet_vars <- function(..., name) {
+  vars_names <- c(...)
+  reserved_names <- c("PANEL", "ROW", "COL", "SCALE_X", "SCALE_Y")
+  problems <- intersect(vars_names, reserved_names)
+  if (length(problems) != 0) {
+    cli::cli_abort(c(
+      "{.val {problems}} {?is/are} not {?an/} allowed name{?/s} for faceting variables",
+      "i" = "Change the name of your data columns to not be {.or {.str {reserved_names}}}"
+    ), call = call2(name))
+  }
+}
 
 #' Get the maximal width/length of a list of grobs
 #'

R/facet-grid-.r

@@ -196,16 +196,18 @@ grid_as_facets_list <- function(rows, cols) {
 FacetGrid <- ggproto("FacetGrid", Facet,
   shrink = TRUE,
 
-  compute_layout = function(data, params) {
+  compute_layout = function(self, data, params) {
     rows <- params$rows
     cols <- params$cols
 
+    check_facet_vars(names(rows), names(cols), name = snake_class(self))
+
     dups <- intersect(names(rows), names(cols))
     if (length(dups) > 0) {
       cli::cli_abort(c(
               "Faceting variables can only appear in {.arg rows} or {.arg cols}, not both.\n",
         "i" = "Duplicated variables: {.val {dups}}"
-      ))
+      ), call = call2(snake_class(self)))
     }
 
     base_rows <- combine_vars(data, params$plot_env, rows, drop = params$drop)

R/facet-wrap.r

@@ -147,6 +147,8 @@ FacetWrap <- ggproto("FacetWrap", Facet,
       return(layout_null())
     }
 
+    check_facet_vars(names(vars), name = snake_class(self))
+
     base <- combine_vars(data, params$plot_env, vars, drop = params$drop)
 
     id <- id(base, drop = TRUE)

tests/testthat/_snaps/facet-layout.md

@@ -39,3 +39,18 @@
 
     Free scales cannot be mixed with a fixed aspect ratio
 
+# facet_wrap and facet_grid throws errors when using reserved words
+
+    "ROW" is not an allowed name for faceting variables
+    i Change the name of your data columns to not be "PANEL", "ROW", "COL", "SCALE_X", or "SCALE_Y"
+
+---
+
+    "ROW" and "PANEL" are not allowed names for faceting variables
+    i Change the name of your data columns to not be "PANEL", "ROW", "COL", "SCALE_X", or "SCALE_Y"
+
+---
+
+    "ROW" is not an allowed name for faceting variables
+    i Change the name of your data columns to not be "PANEL", "ROW", "COL", "SCALE_X", or "SCALE_Y"
+

tests/testthat/test-facet-layout.r

@@ -187,3 +187,15 @@ test_that("facet_grid throws errors at bad layout specs", {
     theme(aspect.ratio = 1)
   expect_snapshot_error(ggplotGrob(p))
 })
+
+test_that("facet_wrap and facet_grid throws errors when using reserved words", {
+  mtcars2 <- mtcars
+  mtcars2$PANEL <- mtcars2$cyl
+  mtcars2$ROW <- mtcars2$gear
+
+  p <- ggplot(mtcars2) +
+    geom_point(aes(mpg, disp))
+  expect_snapshot_error(ggplotGrob(p + facet_grid(ROW ~ gear)))
+  expect_snapshot_error(ggplotGrob(p + facet_grid(ROW ~ PANEL)))
+  expect_snapshot_error(ggplotGrob(p + facet_wrap(~ROW)))
+})