Tab panel functions don't produce Bootstrap 4 compatible markup

[cpsievert]

And as a result, tabsetPanel() et al. don't work well with Bootstrap 4 "plugin" frameworks like Bootswatch 4 or AdminLTE 3, which make strong assumptions about nav (as well as other) markup. In addition to working better with these frameworks, if tabPanel() markup produced the right markup when it's aware that Bootstrap 4 is relevant (via it's {bslib} integration), then folks can also use tabs without the compatibility layer that comes by default with bs_theme()

library(shiny)
library(bslib)

ui <- fluidPage(
  theme = bs_theme() %>% bs_remove("bs3compat"),
  tabsetPanel(
    id = "tabset", type = "pills",
    tabPanel("A", "a"),
    tabPanel("B", "b"),
    navbarMenu(
      "More letters", 
      tabPanel("C", "c"),
      tabPanel("D", "d")
    )
  )
)

server <- function(input, output) {
  observe(print(input$tabset))
}

shinyApp(ui, server)