Function signature_help_to_markdown 

pub fn signature_help_to_markdown(sh: &SignatureHelp) -> String

5.5.LSP.4: render an LSP SignatureHelp payload to a markdown string the popup renderer can display. Picks the active signature (server-supplied active_signature index, default 0) and inlines the active parameter’s documentation when present. Returns the empty string when the response carries no signatures – the caller surfaces “no signature info”.