Don't kill the session when a debounced/throttled reactive expr errors (#3624)

* Don't kill the session when a debounced/throttled reactive expr errors

Fixes #3581

* Update NEWS with PR number

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

Author: jcheng5

NEWS.md

@@ -43,6 +43,8 @@ shiny development
 
 * Closed rstudio/shinytest2#222: When restoring a context (i.e., bookmarking) from a URL, Shiny now better handles a trailing `=` after `_inputs_` and `_values_`. (#3648)
 
+* Closed #3581: Errors in throttled/debounced reactive expressions cause session to exit. (#3624)
+
 
 shiny 1.7.1
 ===========

R/reactives.R

@@ -2472,11 +2472,11 @@ debounce <- function(r, millis, priority = 100, domain = getDefaultReactiveDomai
 
       # Ensure r() is called only after setting firstRun to FALSE since r()
       # may throw an error
-      r()
+      try(r(), silent = TRUE)
       return()
     }
     # This ensures r() is still tracked after firstRun
-    r()
+    try(r(), silent = TRUE)
 
     # The value (or possibly millis) changed. Start or reset the timer.
     v$when <- getDomainTimeMs(domain) + millis()
@@ -2509,7 +2509,7 @@ debounce <- function(r, millis, priority = 100, domain = getDefaultReactiveDomai
   # commenting it out and studying the unit test failure that results.
   primer <- observe({
     primer$destroy()
-    er()
+    try(er(), silent = TRUE)
   }, label = "debounce primer", domain = domain, priority = priority)
 
   er
@@ -2551,7 +2551,7 @@ throttle <- function(r, millis, priority = 100, domain = getDefaultReactiveDomai
   }
 
   # Responsible for tracking when f() changes.
-  observeEvent(r(), {
+  observeEvent(try(r(), silent = TRUE), {
     if (v$pending) {
       # In a blackout period and someone already scheduled; do nothing
     } else if (blackoutMillisLeft() > 0) {

tests/testthat/test-reactives.R

@@ -13,3 +13,28 @@ test_that("can access reactive values directly", {
   y <- reactive(x1() + x2$a)
   expect_equal(y(), 4)
 })
+
+test_that("errors in throttled/debounced reactives are catchable", {
+  reactiveConsole(TRUE)
+  on.exit(reactiveConsole(FALSE))
+
+  # In Shiny 1.7 and earlier, if a throttled/debounced reactive threw an error,
+  # it would cause internal observers used by the implementations of
+  # debounce/throttle to error, which would kill the session. The correct
+  # behavior is to only expose the error to consumers of the throttled/debounced
+  # reactive.
+
+  r <- reactive({
+    stop("boom")
+  })
+
+  rd <- r %>% debounce(1000)
+  rt <- r %>% throttle(1000)
+
+  observe({
+    try(rd(), silent = TRUE)
+    try(rt(), silent = TRUE)
+  })
+
+  expect_silent(flushReact())
+})