I sometimes find myself doing this where I mistakenly use a renderX() in the UI:

library(shiny)

ui <- fluidPage(
  renderTable("table")
)

server <- function(input, output, session) {
  output$table <- renderTable("table")
}

shinyApp(ui, server)

Surprisingly, this doesn't produce any errors, unlike if you mix it up the other way round and put output$table <- tableOutput("table") in the server. Is there anything that could be done to catch it and issue a warning or an error? If not normally, then how about when devmode() is active?