feat: Add toolbar_download_button()

[elnelson575]

Closes #1292
NOTE: The gates can be removed when the latest version of shiny is released.

Summary

Adds toolbar_download_button() to the toolbar component family, providing a download button styled consistently with other toolbar inputs for use in card headers, footers, and other toolbar contexts.

• Adds toolbar_download_button() R function that creates an <a> tag with Shiny's download machinery
• Adds update_toolbar_download_button() for dynamically updating the disabled state
• Adds TypeScript input binding for receiving update messages
• Adds SCSS styles matching toolbar_input_button() patterns
• Includes comprehensive tests with HTML snapshots

Dependencies:

• Depends on: Fix: Allow users to opt out of shiny's download autoenable shiny#4371
• Prerequisite for toolbar download button in py-shiny

Manual Test Cases:

Display:

• Icon only
• Icon + text
• Text Only
• Border
• Other styling

Activation/Deactivation Logic

• enabled = "auto" (default)
• enabled = "TRUE"
• enabled = "FALSE"

Updating:

• Update label
• Update icon
• Update show/hide label
• Multi-update (label + icon + show/hide)

Demo App

Screen.Recording.2026-05-29.at.12.48.59.PM.mov

App Code:

library(shiny)
  library(bslib)

  ui <- page_fluid(
    title = "toolbar_download_button() test",
    tags$style(HTML("
      .row-actions { display: flex; gap: .5rem; flex-wrap: wrap; margin: .5rem 0 1rem; }
      .row-actions .btn { padding: .25rem .5rem; }
    ")),
    tags$h3("Initial variations"),
    card(
      card_header(
        "enabled variations",
        toolbar(
          align = "right",
          toolbar_download_button("dl_auto", label = "auto (default)"),
          toolbar_download_button("dl_true", label = "enabled = TRUE", enabled = TRUE),
          toolbar_download_button("dl_false", label = "enabled = FALSE", enabled = FALSE)
        )
      ),
      tags$small(
        tags$code("auto"), " starts disabled then Shiny auto-enables; ",
        tags$code("TRUE"), " starts enabled (no auto-enable); ",
        tags$code("FALSE"), " starts disabled and stays that way."
      )
    ),
    card(
      card_header(
        "display variations",
        toolbar(
          align = "right",
          toolbar_download_button("dl_label", label = "Show label", show_label = TRUE),
          toolbar_download_button("dl_text_only", label = "Text only", show_label = TRUE, icon = NULL,
  tooltip = FALSE),
          toolbar_download_button("dl_border", label = "Bordered", border = TRUE),
          toolbar_download_button(
            "dl_tooltip",
            label = "Default label",
            tooltip = "Custom tooltip text"
          ),
          toolbar_download_button(
            "dl_icon",
            label = "Custom icon",
            icon = shiny::icon("file-csv")
          ),
          toolbar_download_button(
            "dl_success",
            label = "Export",
            show_label = TRUE,
            class = "btn-success"
          ),
          toolbar_download_button(
            "dl_outline",
            label = "Export",
            show_label = TRUE,
            class = "btn-outline-primary"
          )
        )
      ),
      tags$small("show_label, text-only (no icon), border, custom tooltip, custom icon, btn-success,
  btn-outline-primary.")
    ),
    card(
      card_header(
        "alignment test",
        toolbar(
          align = "right",
          toolbar_input_button(
            "align_btn",
            label = "Filter",
            icon = shiny::icon("filter"),
            show_label = TRUE
          ),
          toolbar_input_select(
            "align_select",
            label = "Region",
            choices = c("All", "North", "South", "East", "West"),
            icon = shiny::icon("globe")
          ),
          toolbar_download_button(
            "align_dl",
            label = "Export",
            show_label = TRUE
          )
        )
      ),
      tags$small("Checks icon + text button, icon select, and icon + text download button sit on the same
   baseline.")
    ),
    tags$hr(),
    tags$h3("Update mechanisms"),
    card(
      card_header(
        "Target",
        toolbar(
          align = "right",
          toolbar_download_button(
            "dl_target",
            label = "Target",
            show_label = TRUE
          )
        )
      ),
      tags$h6("disabled"),
      div(
        class = "row-actions",
        actionButton("disable_t", "disabled = TRUE", class = "btn-sm btn-secondary"),
        actionButton("disable_f", "disabled = FALSE", class = "btn-sm btn-primary")
      ),
      tags$h6("label"),
      div(
        class = "row-actions",
        actionButton("label_a", "label = \"Renamed!\"", class = "btn-sm"),
        actionButton("label_b", "label = \"Download CSV\"", class = "btn-sm"),
        actionButton("label_c", "label = \"Target\"", class = "btn-sm")
      ),
      tags$h6("show_label"),
      div(
        class = "row-actions",
        actionButton("show_t", "show_label = TRUE", class = "btn-sm"),
        actionButton("show_f", "show_label = FALSE", class = "btn-sm")
      ),
      tags$h6("icon"),
      div(
        class = "row-actions",
        actionButton("icon_dl", "icon = download", class = "btn-sm"),
        actionButton("icon_csv", "icon = file-csv", class = "btn-sm"),
        actionButton("icon_save", "icon = floppy-disk", class = "btn-sm")
      ),
      tags$h6("multi-update (label + show_label + icon in one call)"),
      div(
        class = "row-actions",
        actionButton("multi_csv", 'label="Export CSV" + show_label=TRUE + icon=file-csv', class = "btn-sm
   btn-outline-primary"),
        actionButton("multi_save", 'label="Save" + show_label=FALSE + icon=floppy-disk', class = "btn-sm
  btn-outline-primary"),
        actionButton("multi_reset", "reset to defaults", class = "btn-sm btn-outline-secondary")
      ),
      tags$h6("server log"),
      verbatimTextOutput("log")
    )
  )

  server <- function(input, output, session) {
    make_handler <- function(name) {
      downloadHandler(
        filename = function() paste0(name, ".txt"),
        content = function(file) writeLines(paste("hello from", name), file)
      )
    }
    for (id in c(
      "dl_auto", "dl_true", "dl_false",
      "dl_label", "dl_text_only", "dl_border", "dl_tooltip", "dl_icon", "dl_success", "dl_outline",
      "dl_target", "align_dl"
    )) {
      local({
        this_id <- id
        output[[this_id]] <- make_handler(this_id)
      })
    }

    log_lines <- reactiveVal(character())
    log_it <- function(msg) {
      line <- paste0(format(Sys.time(), "%H:%M:%S"), "  ", msg)
      message(line)
      log_lines(c(line, head(log_lines(), 19)))
    }
    output$log <- renderText(paste(log_lines(), collapse = "\n"))

    observeEvent(input$disable_t, {
      log_it("update: disabled = TRUE")
      update_toolbar_download_button("dl_target", disabled = TRUE)
    })
    observeEvent(input$disable_f, {
      log_it("update: disabled = FALSE")
      update_toolbar_download_button("dl_target", disabled = FALSE)
    })

    observeEvent(input$label_a, {
      log_it('update: label = "Renamed!"')
      update_toolbar_download_button("dl_target", label = "Renamed!")
    })
    observeEvent(input$label_b, {
      log_it('update: label = "Download CSV"')
      update_toolbar_download_button("dl_target", label = "Download CSV")
    })
    observeEvent(input$label_c, {
      log_it('update: label = "Target"')
      update_toolbar_download_button("dl_target", label = "Target")
    })

    observeEvent(input$show_t, {
      log_it("update: show_label = TRUE")
      update_toolbar_download_button("dl_target", show_label = TRUE)
    })
    observeEvent(input$show_f, {
      log_it("update: show_label = FALSE")
      update_toolbar_download_button("dl_target", show_label = FALSE)
    })

    observeEvent(input$icon_dl, {
      log_it("update: icon = download")
      update_toolbar_download_button("dl_target", icon = shiny::icon("download"))
    })
    observeEvent(input$icon_csv, {
      log_it("update: icon = file-csv")
      update_toolbar_download_button("dl_target", icon = shiny::icon("file-csv"))
    })
    observeEvent(input$icon_save, {
      log_it("update: icon = floppy-disk")
      update_toolbar_download_button("dl_target", icon = shiny::icon("floppy-disk"))
    })

    observeEvent(input$multi_csv, {
      log_it('multi-update: label="Export CSV", show_label=TRUE, icon=file-csv')
      update_toolbar_download_button(
        "dl_target",
        label = "Export CSV",
        show_label = TRUE,
        icon = shiny::icon("file-csv")
      )
    })
    observeEvent(input$multi_save, {
      log_it('multi-update: label="Save", show_label=FALSE, icon=floppy-disk')
      update_toolbar_download_button(
        "dl_target",
        label = "Save",
        show_label = FALSE,
        icon = shiny::icon("floppy-disk")
      )
    })
    observeEvent(input$multi_reset, {
      log_it('multi-update: reset to label="Target", show_label=TRUE, icon=download')
      update_toolbar_download_button(
        "dl_target",
        label = "Target",
        show_label = TRUE,
        icon = shiny::icon("download")
      )
    })
  }

  shinyApp(ui, server)

Test Plan

• All 162 toolbar tests pass
• TypeScript compiles without errors
• HTML structure matches spec
• Manual verification in Shiny app with downloadHandler()