Catch RenderXXX functions in UI

NEWS.md

@@ -1,5 +1,9 @@
 # shiny (development version)
 
+## Bug fixes and minor improvements
+
+* Using `renderXXX` functions in the UI will now return an error (#4189).
+
 # shiny 1.12.1
 
 ## New features

R/shinywrappers.R

@@ -328,6 +328,12 @@ useRenderFunction <- function(renderFunc, inline = FALSE) {
 #' @export
 #' @method as.tags shiny.render.function
 as.tags.shiny.render.function <- function(x, ..., inline = FALSE) {
+  # return an error when render functions are used in UI
+  if (is.null(getDefaultReactiveDomain())) {
+    stop("There is a renderXXX function in the UI, these should only be used in the server function.",
+         "Use the corresponding XXXOutput function in the UI instead.")
+  }
+
   useRenderFunction(x, inline = inline)
 }
 

tests/testthat/test-shinywrappers.R

@@ -1,3 +1,8 @@
+test_that("render functions in UI throw informative error", {
+  expect_error(as.tags.shiny.render.function(renderTable("table")),
+               "There is a renderXXX function in the UI")
+})
+
 test_that("isTemp passes sanity checks", {
   t <- tempfile(fileext = ".txt")
   writeLines("hello", t)