Snapshot function errors when the output itself is error

Plotly uses snapshotPreprocessOutput to remove any output values that are randomly generated. This is great.

However, if the render function outputs an error, the result is not a valid JSON. Because of this, the snapshotPreprocessOutput function errors out and frameworks like shinytest error out as well.

Example code:

library(plotly)
ui <- fluidPage(
  checkboxInput("go", label="Render plot"),
  plotlyOutput("plot")
)
server <- function(input, output, session) {
  output$plot_plotly <- renderPlotly({
    shiny::req(input$go) #induce a silent.error if input$go is FALSE
    ggplot(data.frame(x=rnorm(1000))) + 
      geom_histogram(aes(x=x))
  })
}
shinyApp(ui=ui, server=server)

Test code:

library(shinytest)
app <- ShinyDriver$new(path="tmp/")
app$getAllValues()

app$getAllValues() reports an error, because fetching the snapshot URL reports an error 500.

The issue can be easily solved in
https://github.com/ropensci/plotly/blob/bcae42bbeea8d8368fb3ca881243e6acd0c661b4/R/shiny.R#L58
I suggest you check if value is a character string before parsing as JSON.

Commencez dans R/shiny.R vers la ligne 58, où snapshotPreprocessOutput analyse la valeur du snapshot. Reproduisez le problème avec l’exemple shinytest fourni, y compris la sortie de renderPlotly qui renvoie une erreur, et vérifiez que app$getAllValues() n’échoue plus lorsque la sortie du snapshot n’est pas un JSON valide.