session$setCurrentTheme should throw an error when trying to dynamically update to a different bootstrap version.

[nstrayer]

Issue

If you're using session$setCurrentTheme() and bslib::bs_theme() together to do dynamic theming, if there is a version mismatch between the original theme and the newly updated dynamic one (such as forgetting to set version in the update code) the theme change will silently change.

Proposed fix

Check to make sure that a dynamic update does not try and change the bootstrap version and throw an error if it does.

Demo app

The following demonstrates the problem. Switching the theme won't work when the version is set to 4 because the initial chosen version was 3. Once you switch the version to 3, then the bootswatch changing starts working.

Steps to reproduce:

• Change theme radio button to "flatly"

  • Nothing will happen

• Change the version radio button to '3'

  • Theme changes now respected

app.R

library(shiny)
library(bslib)

# Setting version to 3 here
my_theme <- bs_theme(bootswatch = "darkly", version = "3")
ui <- fluidPage(
  theme = my_theme,
  radioButtons("current_theme", "Choose a theme for bslib",
               choices = c("darkly", "flatly")),
  radioButtons("bs_version", "Bootstrap version", choices = c("4", "3")),
)

server <- function(input, output, session) {
  observe({
    session$setCurrentTheme(
      bs_theme(bootswatch = input$current_theme, version = input$bs_version)
    )
  })
}

shinyApp(ui, server)

[cpsievert]

Closed via #3210