problems with workingDir in shiny server

[madsurgeon]

I have set up a very basic shiny app and put it into /opt/shiny-server/samples/shiny/.
Shiny server tries and fails to write to my user directory.
Where does it come from?
It uses that wrong directory even when I set the workingDir explicitly with Sys.setenv(R_USER = "/opt/shiny-server/samples/shiny") or shiny::shinyOptions(workingDir = '/opt/shiny-server/samples/shiny').

My app.R:

library(shiny)
library(bslib)

ui <- navbarPage(
  theme = bs_theme(version = 5, bootswatch = 'cyborg'),
  title = "Shiny",
  id = "main-menu",
  tabPanel(
    "First tab",
    h1("First tab"),
    titlePanel("OFGD"),
    sidebarLayout(
      sidebarPanel(
        sliderInput("bins",
                    "Number of bins:",
                    min = 1,
                    max = 50,
                    value = 30)
      ),
      
      mainPanel(
        plotOutput("distPlot")
      )
    )
  ),
  tabPanel(
    "Second tab :-)",
    h1("Second tab")
  )
)

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')
  })
}

shinyApp(ui = ui, server = server)

Last lines in /var/log/shiny-server/shiny-shiny-20240902-083926-46831.log:

Warning in dir.create(cache_dir, recursive = TRUE) :
  cannot create dir '/share/rstudio-home/david/shiny/app_cache', reason 'Permission denied'
Warning in value[[3L]](cond) :
  Error using cache directory at '/share/rstudio-home/david/shiny/app_cache/sass'. Using temp dir instead.

This directory seems not to be set anywhere and still overrides every setting I try to give in the shiny app.
Also, I don't understand, where the sass comes from. I am not explicitly calling it in my code.

Can anyone help?

[AlexisW]

I think bslib::bs_theme() is what calls sass, that tries to cache. See for example here.

Shiny [...] will perform this compilation automatically when handed a bs_theme()

cache This can be a directory to use for the cache, a FileCache object created by sass_file_cache(), or FALSE or NULL for no caching.

Sass caching and precompilation
If Shiny Developer Mode is enabled (by setting options(shiny.devmode = TRUE) or calling shiny::devmode(TRUE)), both sass caching and bslib precompilation are disabled by default; that is, a call to bs_theme_dependencies(theme) expands to bs_theme_dependencies(theme, cache = F, precompiled = F)).

If I understand correctly, you can solve this by setting the option sass.cache or by creating a directory named app_cache/ that will be automatically used.

Also pinging this old question for backlinking.