feat: Fully reload ui/server when autoreload occurs

DESCRIPTION

@@ -93,7 +93,8 @@ Imports:
     glue (>= 1.3.2),
     bslib (>= 0.6.0),
     cachem (>= 1.1.0),
-    lifecycle (>= 0.2.0)
+    lifecycle (>= 0.2.0),
+    watcher 
 Suggests:
     coro (>= 1.1.0),
     datasets,

NEWS.md

@@ -11,6 +11,8 @@
 
 * Shiny's Typescript assets are now compiled to ES2021 instead of ES5. (#4066)
 
+* When auto-reload is enabled, Shiny now reloads the entire app when support files, like Shiny modules, additional script files, or web assets, change. To enable auto-reload, call `devmode(TRUE)` to enable Shiny's developer mode, or set `options(shiny.autoreload = TRUE)` to specifically enable auto-reload. You can choose which files are watched for changes with the `shiny.autoreload.pattern` option. (#4184)
+
 ## Bug fixes
 
 * Fixed a bug with modals where calling `removeModal()` too quickly after `showModal()` would fail to remove the modal if the remove modal message was received while the modal was in the process of being revealed. (#4173)

R/shiny-options.R

@@ -65,16 +65,24 @@ getShinyOption <- function(name, default = NULL) {
 #'   changes are detected, all connected Shiny sessions are reloaded. This
 #'   allows for fast feedback loops when tweaking Shiny UI.
 #'
-#'   Since monitoring for changes is expensive (we simply poll for last
-#'   modified times), this feature is intended only for development.
+#'   Monitoring for changes is no longer expensive, thanks to the \pkg{watcher}
+#'   package, but this feature is still intended only for development.
 #'
 #'   You can customize the file patterns Shiny will monitor by setting the
-#'   shiny.autoreload.pattern option. For example, to monitor only ui.R:
-#'   `options(shiny.autoreload.pattern = glob2rx("ui.R"))`
+#'   shiny.autoreload.pattern option. For example, to monitor only `ui.R`:
+#'   `options(shiny.autoreload.pattern = glob2rx("ui.R"))`. 
+#' 
+#'   Note that because `global.R` is often used for app startup code, changes in
+#'   `global.R` are not applied when using the `ui.R` with `server.R` app file
+#'   pattern.
 #'
-#'   The default polling interval is 500 milliseconds. You can change this
-#'   by setting e.g. `options(shiny.autoreload.interval = 2000)` (every
-#'   two seconds).}
+#'   As mentioned above, Shiny no longer polls watched files for changes.
+#'   Instead, using \pkg{watcher}, Shiny is notified of file changes as they
+#'   occur. These changes are batched together within a customizable latency
+#'   period. You can adjust this period by setting
+#'   `options(shiny.autoreload.interval = 2000)` (in milliseconds). This value
+#'   converted to seconds and passed to the `latency` argument of
+#'   [watcher::watcher()]. The default latency is 250ms.}
 #' \item{shiny.deprecation.messages (defaults to `TRUE`)}{This controls whether messages for
 #'   deprecated functions in Shiny will be printed. See
 #'   [shinyDeprecated()] for more information.}

R/shinyapp.R

@@ -290,33 +290,37 @@ initAutoReloadMonitor <- function(dir) {
     return(function(){})
   }
 
-  filePattern <- getOption("shiny.autoreload.pattern",
-    ".*\\.(r|html?|js|css|png|jpe?g|gif)$")
+  filePattern <- getOption(
+    "shiny.autoreload.pattern",
+    ".*\\.(r|html?|js|css|png|jpe?g|gif)$"
+  )
 
   lastValue <- NULL
-  observeLabel <- paste0("File Auto-Reload - '", basename(dir), "'")
-  obs <- observe(label = observeLabel, {
-    files <- sort_c(
-      list.files(dir, pattern = filePattern, recursive = TRUE, ignore.case = TRUE)
+  check_for_update <- function(paths) {
+    paths <- grep(
+      filePattern,
+      paths,
+      ignore.case = TRUE,
+      value = TRUE
     )
-    times <- file.info(files)$mtime
-    names(times) <- files
-
-    if (is.null(lastValue)) {
-      # First run
-      lastValue <<- times
-    } else if (!identical(lastValue, times)) {
-      # We've changed!
-      lastValue <<- times
-      autoReloadCallbacks$invoke()
+
+    if (length(paths) == 0) {
+      return()
     }
 
-    invalidateLater(getOption("shiny.autoreload.interval", 500))
-  })
+    cachedAutoReloadLastChanged$set()
+    autoReloadCallbacks$invoke()
+  }
 
-  onStop(obs$destroy)
+  # [garrick, 2025-02-20] Shiny <= v1.10.0 used `invalidateLater()` with an
+  # autoreload.interval in ms. {watcher} instead uses a latency parameter in
+  # seconds, which serves a similar purpose and that I'm keeping for backcompat.
+  latency <- getOption("shiny.autoreload.interval", 250) / 1000
+  watcher <- watcher::watcher(dir, check_for_update, latency = latency)
+  watcher$start()
+  onStop(watcher$stop)
 
-  obs$destroy
+  watcher
 }
 
 #' Load an app's supporting R files

R/utils.R

@@ -770,22 +770,45 @@ formatNoSci <- function(x) {
   format(x, scientific = FALSE, digits = 15)
 }
 
+# A simple getter/setting to track the last time the auto-reload process
+# updated. This value is used by `cachedFuncWithFile()` when auto-reload is
+# enabled to reload app/ui/server files when watched supporting files change.
+cachedAutoReloadLastChanged <- local({
+  last_update <- 0
+
+  list(
+    set = function() {
+      last_update <<- as.integer(Sys.time())
+      invisible(last_update)
+    },
+    get = function() {
+      last_update
+    }
+  )
+})
+
 # Returns a function that calls the given func and caches the result for
 # subsequent calls, unless the given file's mtime changes.
 cachedFuncWithFile <- function(dir, file, func, case.sensitive = FALSE) {
-  dir <- normalizePath(dir, mustWork=TRUE)
-  mtime <- NA
+  dir <- normalizePath(dir, mustWork = TRUE)
+
   value <- NULL
+  last_mtime_file <- NA
+  last_autoreload <- 0
+
   function(...) {
-    fname <- if (case.sensitive)
-      file.path(dir, file)
-    else
+    fname <- if (case.sensitive) { 
+      file.path(dir, file) 
+    } else {
       file.path.ci(dir, file)
+    }
 
     now <- file.info(fname)$mtime
-    if (!identical(mtime, now)) {
+    autoreload <- last_autoreload < cachedAutoReloadLastChanged$get()
+    if (autoreload || !identical(last_mtime_file, now)) {
       value <<- func(fname, ...)
-      mtime <<- now
+      last_mtime_file <<- now
+      last_autoreload <<- cachedAutoReloadLastChanged$get()
     }
     value
   }