Friendlier error when supplying extension-less files (#5202)

Author: MichaelChirico

R/save.r

@@ -238,6 +238,9 @@ plot_dev <- function(device, filename = NULL, dpi = 300, call = caller_env()) {
 
   if (is.null(device)) {
     device <- to_lower_ascii(tools::file_ext(filename))
+    if (identical(device, "")) {
+      cli::cli_abort("{.arg filename} has no file extension and {.arg device} is {.val NULL}.", call = call)
+    }
   }
 
   if (!is.character(device) || length(device) != 1) {

tests/testthat/test-ggsave.R

@@ -74,6 +74,14 @@ test_that("ggsave warns about empty or multiple filenames", {
   )
 })
 
+test_that("ggsave fails informatively for no-extension filenames", {
+  plot <- ggplot(mtcars, aes(disp, mpg)) + geom_point()
+  expect_error(
+    ggsave(tempfile(), plot),
+    '`filename` has no file extension and `device` is "NULL"'
+  )
+})
+
 # plot_dim ---------------------------------------------------------------
 
 test_that("guesses and informs if dim not specified", {