Shiny Apps: is it possible to render HTML in validation messages?

Question

Is there any way to render HTML in shiny's validation messages? I tried different approaches using the HTML wrapper, the tags$... functions, as well as a separate htmlOutput for the validation message, but could not get any of them to work. Here is a simple example app that shows this issue - the select should be bold in the validation message but the HTML tags are escaped (contrived example, I know, but hopefully conveys the idea, I would primarily like to use this to include fa icons in the messages):

runApp(
  list(
    ui = fluidPage(

      titlePanel("Validation App"),

      sidebarLayout(
        sidebarPanel(
          selectInput("data", label = "Data set", choices = c("", "mtcars"))
        ),

        mainPanel(tableOutput("table"))
      )
    ),

    server = function(input, output) {

      data <- reactive({ 

        # validate test
        validate(
          need(input$data != "", HTML("Please <strong>select</strong> a data set"))
        )

        get(input$data, 'package:datasets') 
      })

      output$table <- renderTable(head(data()))

    }

  )
)

Answer 1

The simplest solution is to use a uiOutput and inside the renderUI function put an if to validate the input. In the code below is an example using HTML and tags$... functions. You can can also put an icon.

library(shiny)
runApp(
  list(
    ui = fluidPage(
      titlePanel("Validation App"),
      sidebarLayout(
        sidebarPanel(
          selectInput("data", label = "Data set", choices = c("", "mtcars"))
        ),
        mainPanel(uiOutput("tableUI"))
      )
    ),

    server = function(input, output) {
      data <- reactive({ 
        get(input$data, 'package:datasets') 
      })

      output$tableUI <- renderUI({
        if (input$data == "") {
          div(
            HTML("Please <strong>select</strong> a data set"),
            tags$p(icon("exclamation"), "Please",tags$strong("select"), "a data set")
          ) 
        } else {
          tableOutput("table")
        }
      })

      output$table <- renderTable(head(data()))
    }

  )
)