Incomplete stack trace reported when code in a shiny app observer fails

[mlell]

When testing code happening with test_that() inside a shiny app using shiny::testServer() and an error happens inside shiny::observeEvent({...}) the error location is not reported in the stack trace generated by test_that(). It is only reported by the default handler output that is generated by shiny. In the reproducible example, the stack trace stops at setInputs() rather than following the functions that are called as a results of setInputs() being called.

The expected result would be that testthat and shiny report the same error source, the function "stop()" in the function x(), and give as file and line number test.R:6.

Example application or steps to reproduce the problem

# File "test.R"
library(testthat)
library(shiny)

x <- function(a){
  stop("test")
}

testServer(list(
  ui = flowLayout(actionButton("button", "Push me")), 
  server = function(input, output, session){
    observeEvent(input$button, {
      rlang::try_fetch(
      x(3)
      , error = function(e) rlang::abort("Error in observer", parent = e)
    )
  })
    
  }), {
  test_that("x",{
    session$setInputs(button = 1L)
  })
})

Output:

# [ Full `shiny` stack trace =============================================== ]
  131: <Anonymous>
  130: signalCondition
  129: signal_abort [/tmp/RtmpXwi0DI/R.INSTALL279488583bf75f/rlang/R/cnd-abort.R#861]
  128: rlang::abort [/tmp/RtmpXwi0DI/R.INSTALL279488583bf75f/rlang/R/cnd-abort.R#390]
  127: handlers[[1L]] [~/test.R#14]
  126: h [/tmp/RtmpXwi0DI/R.INSTALL279488583bf75f/rlang/R/cnd-handlers.R#223]
  125: .handleSimpleError
  124: stop
  123: x [~/test.R#5]
  116: observe [~/test.R#12]
  115: <observer:observeEvent(input$button)> [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/utils.R#1459]
  113: valueFunc [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/utils.R#1449]
   96: func [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/bind-event.R#298]
   94: f [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/utils.R#1532]
   93: Reduce
   84: do [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/utils.R#1518]
   83: hybrid_chain [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/utils.R#1558]
   82: observeEvent(input$button) [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/bind-event.R#280]
   81: contextFunc [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/utils.R#1451]
   80: env$runWith [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/react.R#160]
   69: ctx$run [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/react.R#54]
   68: run [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/reactives.R#1234]
   49: flushCallback [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/reactives.R#1204]
   48: FUN [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/react.R#114]
   47: lapply
   46: ctx$executeFlushCallbacks [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/react.R#113]
   45: .getReactiveEnvironment()$flush [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/react.R#182]
   44: shiny:::flushReact [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/react.R#202]
   43: private$flush [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/mock-session.R#692]
   42: session$setInputs [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/mock-session.R#370]
   41: eval [~/test.R#20]
   40: eval
   31: test_code [/tmp/RtmpXdwe80/R.INSTALLf9c3cb9ccd7/r-lib-testthat-dbe8883/R/test-that.R#188]
   30: test_that [/tmp/RtmpXdwe80/R.INSTALLf9c3cb9ccd7/r-lib-testthat-dbe8883/R/test-that.R#53]
   29: rlang::eval_tidy [~/test.R#19]
    5: testServer [/tmp/Rtmp2wImAI/R.INSTALLe8961d20769/rstudio-shiny-9a35b01/R/test-server.R#121]
    4: eval [~/test.R#8]
    3: eval
    1: source
── Warning: x ─────────────────────────
Error in observe: Error in observer
Caused by error in `x()`:
! test
# [ Incomplete "test_that" stack trace ================================= ]
Backtrace:
     ▆
  1. └─session$setInputs(button = 1L) at ~/test.R:20:5
  2.   └─private$flush() at rstudio-shiny-9a35b01/R/mock-session.R:370:7
  3.     └─shiny:::flushReact() at rstudio-shiny-9a35b01/R/mock-session.R:692:7
  4.       └─.getReactiveEnvironment()$flush() at rstudio-shiny-9a35b01/R/react.R:202:3
  5.         └─ctx$executeFlushCallbacks() at rstudio-shiny-9a35b01/R/react.R:182:9
  6.           └─base::lapply(...) at rstudio-shiny-9a35b01/R/react.R:113:7
  7.             └─shiny (local) FUN(X[[i]], ...)
  8.               └─shiny (local) flushCallback() at rstudio-shiny-9a35b01/R/react.R:114:9
  9.                 └─shiny:::hybrid_chain(...) at rstudio-shiny-9a35b01/R/reactives.R:1204:9
 10.                   └─shiny (local) do() at rstudio-shiny-9a35b01/R/utils.R:1558:5
 11.                     └─base::tryCatch(...) at rstudio-shiny-9a35b01/R/utils.R:1518:5
 12.                       └─base (local) tryCatchList(expr, classes, parentenv, handlers)
 13.                         └─base (local) tryCatchOne(expr, names, parentenv, handlers[[1L]])
 14.                           └─value[[3L]](cond)
 15.                             └─shiny (local) catch(e) at rstudio-shiny-9a35b01/R/utils.R:1546:9
 16.                               └─shiny::printError(e) at rstudio-shiny-9a35b01/R/reactives.R:1220:13

── Skip: x ────────────────────────────
Reason: empty test

System details

Browser Version: n/a

Output of sessionInfo():

R version 4.2.2 Patched (2022-11-10 r83330)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Debian GNU/Linux 12 (bookworm)

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.11.0
LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.11.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8    LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices datasets  utils     methods   base     

other attached packages:
[1] testthat_3.2.1.1 shiny_1.9.1.9000

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.13       rstudioapi_0.16.0 magrittr_2.0.3    pkgload_1.4.0     xtable_1.8-4      R6_2.5.1          rlang_1.1.4      
 [8] fastmap_1.2.0     tools_4.2.2       waldo_0.6.1       cli_3.6.3         withr_3.0.1       htmltools_0.5.8.1 digest_0.6.37    
[15] rprojroot_2.0.4   lifecycle_1.0.4   crayon_1.5.3      brio_1.1.5        later_1.3.2       promises_1.3.2    cachem_1.1.0     
[22] mime_0.12         compiler_4.2.2    desc_1.4.3        httpuv_1.6.15     renv_1.0.7 

[hadley]

Thanks for filing this bug report! Unfortunately because it's unlikely to affect many people and it's likely going to be very hard to run down, we don't have the development resources to fix it at this time. It's our policy to close such issues to help stay focussed on the biggest problems, but the issue is still indexed by google, so if other people hit it, they'll be able to find it, and we can consider reopen it if it turns out to be a common problem. Thanks for reporting and I'm sorry we couldn't help more 😞.