feat: Run examples from any package (#4005)

* chore: `inst/shiny` -> `inst/examples-shiny`

* feat(runExamples): Find examples in any package

* refactor: code style

* refactor: small code style changes

* docs: fix runApp typo

* chore: include package name in valid examples message

* chore(runExample): check that `package` is installed

* chore: use braced package name

* Update news

---------

Co-authored-by: Carson Sievert <[email protected]>

NEWS.md

@@ -16,6 +16,8 @@
 
 * Added `onUnhandledError()` to register a function that will be called when an unhandled error occurs in a Shiny app. Note that this handler doesn't stop the error or prevent the session from closing, but it can be used to log the error or to clean up session-specific resources. (thanks @JohnCoene, #3993)
 
+* `runExamples()` now uses the `{bslib}` package to build the user interface (UI). It also gains a `package` argument so that other packages can leverage this same function to run Shiny app examples. For more, see `?runExamples`. (#3963, #4005)
+
 ## Bug fixes
 
 * Notifications are now constrained to the width of the viewport for window widths smaller the default notification panel size. (#3949)

R/runapp.R

@@ -447,6 +447,16 @@ stopApp <- function(returnValue = invisible()) {
 #' @param display.mode The mode in which to display the example. Defaults to
 #'   `showcase`, but may be set to `normal` to see the example without
 #'   code or commentary.
+#' @param package The package in which to find the example (defaults to
+#'   `"shiny"`).
+#'
+#'   To provide examples in your package, store examples in the
+#'   `inst/examples-shiny` directory of your package. Each example should be
+#'   in its own subdirectory and should be runnable when [runApp()] is called
+#'   on the subdirectory. Example apps can include a `DESCRIPTION` file and a
+#'   `README.md` file to provide metadata and commentary about the example. See
+#'   the article on [Display Modes](https://shiny.posit.co/r/articles/build/display-modes/)
+#'   on the Shiny website for more information.
 #' @inheritParams runApp
 #'
 #' @examples
@@ -462,34 +472,46 @@ stopApp <- function(returnValue = invisible()) {
 #'   system.file("examples", package="shiny")
 #' }
 #' @export
-runExample <- function(example=NA,
-                       port=getOption("shiny.port"),
-                       launch.browser = getOption('shiny.launch.browser', interactive()),
-                       host=getOption('shiny.host', '127.0.0.1'),
-                       display.mode=c("auto", "normal", "showcase")) {
-  legacy <- getOption('shiny.legacy.examples', FALSE)
-  examplesDir <- if (isTRUE(legacy)) 'examples' else 'examples-shiny'
-  examplesDir <- system_file(examplesDir, package='shiny')
+runExample <- function(
+  example = NA,
+  port = getOption("shiny.port"),
+  launch.browser = getOption("shiny.launch.browser", interactive()),
+  host = getOption("shiny.host", "127.0.0.1"),
+  display.mode = c("auto", "normal", "showcase"),
+  package = "shiny"
+) {
+  if (!identical(package, "shiny") && !is_installed(package)) {
+    rlang::check_installed(package)
+  }
+
+  use_legacy_shiny_examples <-
+    identical(package, "shiny") &&
+    isTRUE(getOption('shiny.legacy.examples', FALSE))
+
+  examplesDir <- system_file(
+    if (use_legacy_shiny_examples) "examples" else "examples-shiny",
+    package = package
+  )
+
   dir <- resolve(examplesDir, example)
+
   if (is.null(dir)) {
+    valid_examples <- sprintf(
+      'Valid examples in {%s}: "%s"',
+      package,
+      paste(list.files(examplesDir), collapse = '", "')
+    )
+
     if (is.na(example)) {
-      errFun <- message
-      errMsg <- ''
-    }
-    else {
-      errFun <- stop
-      errMsg <- paste('Example', example, 'does not exist. ')
+      message(valid_examples)
+      return(invisible())
     }
 
-    errFun(errMsg,
-           'Valid examples are "',
-           paste(list.files(examplesDir), collapse='", "'),
-           '"')
-  }
-  else {
-    runApp(dir, port = port, host = host, launch.browser = launch.browser,
-           display.mode = display.mode)
+    stop("Example '", example, "' does not exist. ", valid_examples)
   }
+
+  runApp(dir, port = port, host = host, launch.browser = launch.browser,
+         display.mode = display.mode)
 }
 
 #' Run a gadget