[Bug]: Conditional toolbar item throws `ToolbarError.badChildCount`, potentially crashing app

[nighthawk]

What happened?

If you have a stylesheet like this:

  ~SHEET"""
    "comments-stack" do
      toolbar(content: :toolbar)
      toolbar(content: :toolbar_button)
      toolbar(content: :cancel_button)
    end

and only conditionally show one of the toolbar items like:

  <%= if @show_cancel do %>
    <ToolbarItem template="cancel_button" placement="cancellationAction">
      <Button phx-click="cancel">Close</Button>
    </ToolbarItem>
  <% end %>

you'll get ToolbarError.badChildCount(0) thrown at runtime.

This ended up crashing my app, as I use a custom registry, which gets this default implementation:

extension CustomRegistry where ErrorView == Never {
    /// A default implementation that falls back to the default framework error view.
    public static func errorView(for error: Error) -> Never {
        fatalError()
    }
}

---

Not a big issue, as I can work around this by putting then <%= if ... %> around the button rather than the toolbar item, but I wouldn't have expected this to throw an error (or crash the app). It'd be nice if this was handled more gracefully.

Library Version

0.4.0-rc.1

Xcode Version

Version 16.2 (16C5032a)

Swift Version

No response

On which device or simulator are you running into the problem?

iPhone

Target Device Operating System Version

iOS 18

Relevant log output