Embedded shinyApp() doesn't fill container's height

[SiSch90]

As @cpsievert already described in another thread, upgrading from rmarkdown 2.5 to 2.6 adds an additional <p> around the <iframe>, which apparently causes the display problems of flexdashboards in shiny environment described below.

@cderv minimal example based on shiny demo app:

---
title: "Test"
output: 
  flexdashboard::flex_dashboard
runtime: shiny
---

```{r}
ui <- fluidPage(titlePanel("Hello Shiny!"),
                sidebarLayout(sidebarPanel(
                  sliderInput(
                    inputId = "bins",
                    label = "Number of bins:",
                    min = 1,
                    max = 50,
                    value = 30
                  )
                ),
                mainPanel(plotOutput(outputId = "distPlot"))))
server <- function(input, output) {
  output$distPlot <- renderPlot({
    x    <- faithful$waiting
    bins <- seq(min(x), max(x), length.out = input$bins + 1)
    hist(
      x,
      breaks = bins,
      col = "#75AADB",
      border = "white",
      xlab = "Waiting time to next eruption (in mins)",
      main = "Histogram of waiting times"
    )
  })
}
shinyApp(ui, server)

Session Info:
R version 4.1.0 (2021-05-18)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 14393)

Matrix products: default

locale:
[1] LC_COLLATE=German_Germany.1252 LC_CTYPE=German_Germany.1252 LC_MONETARY=German_Germany.1252 LC_NUMERIC=C
[5] LC_TIME=German_Germany.1252

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

loaded via a namespace (and not attached):
[1] htmlwidgets_1.5.4 compiler_4.1.0 magrittr_2.0.1 fastmap_1.1.0 htmltools_0.5.2 tools_4.1.0 flexdashboard_0.5.2
[8] yaml_2.2.1 DT_0.19 rmarkdown_2.11 knitr_1.36 jsonlite_1.7.2 xfun_0.24 digest_0.6.27
[15] rlang_0.4.11 evaluate_0.14

[cpsievert]

We'll likely provide a real fix for this, but in the meantime, you can fix it by doing:

withr::with_options(
  list(htmltools.preserve.raw = FALSE),
  rmarkdown::run("reprex.Rmd")
)

[cpsievert]

Closing since we've identified and fixed the core issue here rstudio/htmltools#305

The "real" fix for this issue will be to install/upgrade to a new version of htmltools (and for now you'll have to do remotes::install_github("rstudio/htmltools"))

[cderv]

Thanks @cpsievert !