Client error console and duplicate input/output binding errors

[nstrayer]

What?

This PR adds a client-side error console for surfacing errors to the user that previously would go unseen unless they had their browser's devtools open.

Also included is special detection of duplicate input and output bindings which would previously silently either break your app (in the case of outputs) or cause confusing behavior (only first bound input would work.)

There is support for multiple errors:

The following test app will trigger input and output binding errors. (Note you'll need to comment out the second output to get the input error to show up because output binding errors stop the entire Shiny runtime.

library(shiny)

ui <- fluidPage(

    # Application title
    titlePanel("Old Faithful Geyser Data"),

    # Sidebar with a slider input for number of bins
    sidebarLayout(
        sidebarPanel(
            sliderInput("bins",
                        "Number of bins:",
                        min = 1,
                        max = 50,
                        value = 30),
            numericInput("bins","Number of bins:",value = 30)
        ),
        mainPanel(
           # Multiple binding collisions will be caught and displayed in a
           # single error message
           plotOutput("distPlot", width = "50%"),
           plotOutput("distPlot"),
           plotOutput("secondPlot", width = "50%"),
           plotOutput("secondPlot")
        )
    )
)

server <- function(input, output) {
    output$distPlot <- renderPlot({
        # generate bins based on input$bins from ui.R
        x    <- faithful[, 2]
        bins <- seq(min(x), max(x), length.out = input$bins + 1)

        # draw the histogram with the specified number of bins
        hist(x, breaks = bins, col = 'darkgray', border = 'white',
             xlab = 'Waiting time to next eruption (in mins)',
             main = 'Histogram of waiting times')
    })
}

# Run the application
shinyApp(ui = ui, server = server)

How?

Adds two webcomponents: shiny-error-console-container and shiny-error-console. A function showErrorInClientConsole(e) adds the errors to the page (as children of a shiny-error-console-container for layout purposes) as they come in.

[nstrayer]

App that shows catching of duplicate IDs across static and dynamic UI

library(shiny)

ui <- fluidPage(
    sidebarLayout(
        sidebarPanel(
            sliderInput("bins",
                        "Number of bins:",
                        min = 1,
                        max = 50,
                        value = 30),
            checkboxInput("showDynamicPlot", "Show dynamic plot")
        ),
        mainPanel(
           plotOutput("distPlot"),
           # Uncomment this line to trigger initialization duplicate error
           # plotOutput("distPlot", width = "50%"),
           uiOutput("dynamicPlot"),
        )
    )
)

server <- function(input, output) {

    output$distPlot <- renderPlot({
        x    <- faithful[, 2]
        bins <- seq(min(x), max(x), length.out = input$bins + 1)

        hist(x, breaks = bins, col = 'darkgray', border = 'white',
             xlab = 'Waiting time to next eruption (in mins)',
             main = 'Histogram of waiting times')
    })

    output$dynamicPlot <- renderUI({
      if (input$showDynamicPlot) {
        sliderInput("bins",
          "Number of bins:",
          min = 1,
          max = 50,
          value = 30)
      }
    })
}

shinyApp(ui = ui, server = server)

[nstrayer]

The latest commit changes the styles so that the container component holds most of the logic. Also adds a dismiss button and a collapse button.

[michaelhogersnplm]

Hello @nstrayer, great addition - it certainly has the potential to reduce confusion occasionally. I'm curious, though: could there be a feature to switch this off, perhaps through a setting, for instances where it might be preferable to keep it concealed in a production environment?

Best,
Michael

[CLAassistant]

All committers have signed the CLA.

[nstrayer]

Hello @nstrayer, great addition - it certainly has the potential to reduce confusion occasionally. I'm curious, though: could there be a feature to switch this off, perhaps through a setting, for instances where it might be preferable to keep it concealed in a production environment?

Best, Michael

Hi Michael,

This is a good point. Right now this only should catch errors that would have otherwise broken your app. We're going to try bringing it in where it is always active and then run our large suite of tests on Shiny to see if we're going to start causing spurious error messages to appear. If it becomes a problem then the plan would be to make it only show up when devmode is turned on for Shiny.

[nstrayer]

In 34cf27e, I switched where the logic for throwing on duplicate ID bindings was. Now we let Shiny run through all the input and output bindings. Then after both bindInputs() and bindOtuputs() have run, we validate and throw a much more helpful error message that contains all the duplicates. This means we can get error messages like this:

The following IDs were repeated: 
"vars": (2 inputs and 1 output), 
"bins": (2 inputs)

[nstrayer]

This is what the current error messages look like, since the previous screenshots are out-of-date:

[wch]

Fix comment

[wch]

Rename to checkValidity.

[wch]

Use a more efficient copying technique.