feat: Fully reload ui/server when autoreload occurs (#4184)

* feat: Fully reload ui/server when autoreload occurs

* chore: remove stray empty line

* chore: clean up function names and add comments

* docs: Add news item

* feat: Use {watcher} for autoreload file watching (#4185)

* feat: Use {watcher}

* chore: shikokuchuo/watcher@dev

* chore: watcher is on CRAN now

* chore: Undo air format changes

* feat: Use `shiny.autoreload.interval` for watcher latency

* chore: Simply track last time auto-reload changed

* docs: rewrite options docs for clarity

* chore: code style

* docs: global.R changes are not applied

* feat(ui/server): Autoreload also reloads global and R support files

* chore: remove outdated comment

* chore: safer comparisons

* chore: Restore legacy autoreload watcher if {watcher} not installed

* rename: autoload_r_support_if_needed()

* chore: use `rlang::is_false()`

* chore: use_build_ignore("_dev")

Author: gadenbuie

.Rbuildignore

@@ -36,3 +36,4 @@
 ^\.browserslistrc$
 ^\.eslintrc\.yml$
 ^\.yarnrc\.yml$
+^_dev$

DESCRIPTION

@@ -111,7 +111,8 @@ Suggests:
     dygraphs,
     ragg,
     showtext,
-    sass
+    sass,
+    watcher 
 URL: https://shiny.posit.co/,
     https://github.com/rstudio/shiny
 BugReports: https://github.com/rstudio/shiny/issues

NEWS.md

@@ -13,6 +13,8 @@
 
 * `textInput()`, `textAreaInput()`, `numericInput()` and `passwordInput()` all gain an `updateOn` option. `updateOn = "change"` is the default and previous behavior, where the input value updates immediately whenever the value changes. With `updateOn = "blur"`, the input value will update only when the text input loses focus or when the user presses Enter (or Cmd/Ctrl + Enter for `textAreaInput()`). (#4183)
 
+* 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 +65,20 @@ 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"))`. 
 #'
-#'   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

@@ -162,11 +162,29 @@ shinyAppDir_serverR <- function(appDir, options=list()) {
     sharedEnv <- globalenv()
   }
 
+  # To enable hot-reloading of support files, this function is called
+  # whenever the UI or Server func source is updated. To avoid loading
+  # support files 2x, we follow the last cache update trigger timestamp.
+  autoload_r_support_if_needed <- local({
+    autoload_last_loaded <- -1
+    function() {
+      if (!isTRUE(getOption("shiny.autoload.r", TRUE))) return()
+      
+      last_cache_trigger <- cachedAutoReloadLastChanged$get()
+      if (identical(autoload_last_loaded, last_cache_trigger)) return()
+
+      loadSupport(appDir, renv = sharedEnv, globalrenv = globalenv())
+
+      autoload_last_loaded <<- last_cache_trigger
+    }
+  })
+
   # uiHandlerSource is a function that returns an HTTP handler for serving up
   # ui.R as a webpage. The "cachedFuncWithFile" call makes sure that the closure
   # we're creating here only gets executed when ui.R's contents change.
   uiHandlerSource <- cachedFuncWithFile(appDir, "ui.R", case.sensitive = FALSE,
     function(uiR) {
+      autoload_r_support_if_needed()
       if (file.exists(uiR)) {
         # If ui.R contains a call to shinyUI (which sets .globals$ui), use that.
         # If not, then take the last expression that's returned from ui.R.
@@ -197,6 +215,7 @@ shinyAppDir_serverR <- function(appDir, options=list()) {
 
   serverSource <- cachedFuncWithFile(appDir, "server.R", case.sensitive = FALSE,
     function(serverR) {
+      autoload_r_support_if_needed()
       # If server.R contains a call to shinyServer (which sets .globals$server),
       # use that. If not, then take the last expression that's returned from
       # server.R.
@@ -232,10 +251,9 @@ shinyAppDir_serverR <- function(appDir, options=list()) {
   onStart <- function() {
     oldwd <<- getwd()
     setwd(appDir)
-    # TODO: we should support hot reloading on global.R and R/*.R changes.
     if (getOption("shiny.autoload.r", TRUE)) {
-      loadSupport(appDir, renv=sharedEnv, globalrenv=globalenv())
-    }  else {
+      autoload_r_support_if_needed()
+    } else {
       if (file.exists(file.path.ci(appDir, "global.R")))
         sourceUTF8(file.path.ci(appDir, "global.R"))
     }
@@ -290,33 +308,77 @@ 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)
-    )
-    times <- file.info(files)$mtime
-    names(times) <- files
-
-    if (is.null(lastValue)) {
-      # First run
-      lastValue <<- times
-    } else if (!identical(lastValue, times)) {
-      # We've changed!
-      lastValue <<- times
+  
+  if (is_installed("watcher")) {
+    check_for_update <- function(paths) {
+      paths <- grep(
+        filePattern,
+        paths,
+        ignore.case = TRUE,
+        value = TRUE
+      )
+      
+      if (length(paths) == 0) {
+        return()
+      }
+      
+      cachedAutoReloadLastChanged$set()
       autoReloadCallbacks$invoke()
     }
+    
+    # [garrick, 2025-02-20] Shiny <= v1.10.0 used `invalidateLater()` with an
+    # autoreload.interval in ms. {watcher} instead uses a latency parameter in
+    # seconds, which serves a similar purpose and that I'm keeping for backcompat.
+    latency <- getOption("shiny.autoreload.interval", 250) / 1000
+    watcher <- watcher::watcher(dir, check_for_update, latency = latency)
+    watcher$start()
+    onStop(watcher$stop)
+  } else {
+    # Fall back to legacy observer behavior
+    if (!is_false(getOption("shiny.autoreload.legacy_warning", TRUE))) {
+      cli::cli_warn(
+        c(
+          "Using legacy autoreload file watching. Please install {.pkg watcher} for a more performant autoreload file watcher.",
+          "i" = "Set {.run options(shiny.autoreload.legacy_warning = FALSE)} to suppress this warning."
+        ),
+        .frequency = "regularly",
+        .frequency_id = "shiny.autoreload.legacy_warning"
+      )
+    }
 
-    invalidateLater(getOption("shiny.autoreload.interval", 500))
-  })
-
-  onStop(obs$destroy)
+    lastValue <- NULL
+    observeLabel <- paste0("File Auto-Reload - '", basename(dir), "'")
+    watcher <- observe(label = observeLabel, {
+      files <- sort_c(
+        list.files(dir, pattern = filePattern, recursive = TRUE, ignore.case = TRUE)
+      )
+      times <- file.info(files)$mtime
+      names(times) <- files
+  
+      if (is.null(lastValue)) {
+        # First run
+        lastValue <<- times
+      } else if (!identical(lastValue, times)) {
+        # We've changed!
+        lastValue <<- times
+        cachedAutoReloadLastChanged$set()
+        autoReloadCallbacks$invoke()
+      }
+  
+      invalidateLater(getOption("shiny.autoreload.interval", 500))
+    })
+  
+    onStop(watcher$destroy)
+  
+    watcher$destroy
+  }
 
-  obs$destroy
+  invisible(watcher)
 }
 
 #' Load an app's supporting R files
@@ -421,8 +483,6 @@ shinyAppDir_appR <- function(fileName, appDir, options=list())
       wasDir <- setwd(appDir)
       on.exit(setwd(wasDir))
 
-      # TODO: we should support hot reloading on R/*.R changes.
-      # In an upcoming version of shiny, this option will go away.
       if (getOption("shiny.autoload.r", TRUE)) {
         # Create a child env which contains all the helpers and will be the shared parent
         # of the ui.R and server.R load.

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
   }