feat: add a warning for direct rhino::app() calls

The encouraged way to run a Rhino app is shiny::runApp(). Using runApp
allows for shiny.autoreload (and possibly other features) to work.

R/app.R

@@ -77,7 +77,8 @@ with_head_tags <- function(ui) {
 #' Rhino application
 #'
 #' The entrypoint for a Rhino application.
-#' Your `app.R` should contain nothing but a call to `rhino::app()`.
+#' Your `app.R` should contain nothing but a call to `rhino::app()`,
+#' and the app should be started with `shiny::runApp()`.
 #'
 #' This function is a wrapper around `shiny::shinyApp()`.
 #' It reads `rhino.yml` and performs some configuration steps (logger, static files, box modules).
@@ -87,6 +88,10 @@ with_head_tags <- function(ui) {
 #' It should export two functions which take a single `id` argument -
 #' the `ui` and `server` of your top-level Shiny module.
 #'
+#' Using `rhino::app()` directly is discouraged.
+#' Being a wrapper around `shiny::shinyApp()`,
+#' it does not allow features such as shiny.autoreload to work.
+#'
 #' # Legacy entrypoint
 #'
 #' It is possible to specify a different way to load your application
@@ -110,6 +115,9 @@ with_head_tags <- function(ui) {
 #' into a [Shiny module](https://shiny.rstudio.com/articles/modules.html)
 #' (functions taking a single `id` argument).
 #'
+#' @param warn_on_direct_call `TRUE` by default. Set to `FALSE` to squelch warning when calling
+#' `rhino::app()` directly.
+#'
 #' @return An object representing the app (can be passed to `shiny::runApp()`).
 #'
 #' @examples
@@ -118,7 +126,19 @@ with_head_tags <- function(ui) {
 #'   rhino::app()
 #' }
 #' @export
-app <- function() {
+app <- function(warn_on_direct_call = TRUE) {
+  is_direct_call <- identical(parent.frame(), .GlobalEnv)
+  if (isTRUE(warn_on_direct_call) && isTRUE(is_direct_call)) {
+    cli::cli_warn(
+      c(
+        "!" = paste(
+          "{.code rhino::app()} shouldn't be used directly.",
+          "Please use {.code shiny::runApp()} instead."
+        ),
+        "i" = "To squelch this warning set {.code warn_on_direct_call = TRUE}."
+      )
+    )
+  }
   setup_box_path()
   box::purge_cache()
   configure_logger()