Call shiny ui in a parent module and server in child module

[Krye.Kuzhinieri]

I have a shiny application which uses nested modules. What I would like to do is call a shiny module ui in a grandparent's ui and the shiny server in the grandchild server. Here is a simple example:

library(shiny)

sub_module_b_ui <- function(id) {
  ns <- NS(id)
  sliderInput(
    inputId = ns("slider"),
    label = "my slider",
    min = 1,
    max = 100,
    value = 20,
    step = 1,
  )
}

#' @export
sub_module_b_server <- function(id) {
  moduleServer(id, function(input, output, session) {
    observeEvent(input$slider, {
      print(input$slider)
    })
  })
}

sub_module_a_server <- function(id, parent_ns) {
  moduleServer(id, function(input, output, session) {
    sub_module_b_server(id = "filters")
  })
}

main_module_ui <- function(id) {
  ns <- NS(id)
  sub_module_b_ui(id = ns("filters"))
}

#' @export
main_module_server <- function(id) {
  moduleServer(id, function(input, output, session) {
    ns <- session$ns
    sub_module_a_server(id = "sub_module_a", parent_ns = ns)
  })
}

ui <- fluidPage(
  tags$h1("My page"),
  main_module_ui(id = "main_module")
)

server <- function(input, output) {
  main_module_server(id = "main_module")
}

shinyApp(ui = ui, server = server)

To explain a bit further, this is the hierarchy:

• Shiny application
  " --- main module"
  " ---------- sub module a"
  " ---------------- sub module b"

What I am really trying to achieve is call sub_module_b_ui inside of main_module_ui. And call sub_module_b_server inside of the sub_module_a_server. To me it does not seem related to namespaces because even when I manually type the input id:

sub_module_b_server <- function(id) {
  moduleServer(id, function(input, output, session) {
    observeEvent(input[["main_module-filters-slider"], {
      print(input$slider)
    })
  })
}

the observe even does not trigger the event.

Would appreciate anyone's help.