TypeScript LSP status in Airline

nvim_lsp_status_airline.lua

-- The TypeScript LSP server takes a while before it's responsive. This is a janky way of indicating the server status in
-- airline. It works by adding "..." to the statusline when the LSP connects, and then removing the "..." when the first
-- set of diagnostics come in.

vim.cmd([[
  let g:lsp_wait_added = 0
  let g:lsp_wait_done = 0
  function! LspWait(...)
      let builder = a:1
      let context = a:2
      call builder.add_section('airline_b', '...')
      return 0
  endfunction
]])

local function on_attach(client, bufnr)
  
  -- add the "..." to airline when the lsp server connects
  vim.cmd([[
    if !g:lsp_wait_added
      call airline#add_statusline_func('LspWait')
      call airline#add_inactive_statusline_func('LspWait')
      call airline#update_statusline()
      let g:lsp_wait_added = 1
    endif
  ]])

  -- remove the "..." when the lsp server sends diagnostics for the first time
  -- note: I originally wanted to listen for progress events, but typescript-language-server
  --       doesn't seem to send any even when I specify the capabilities.
  local handler = vim.lsp.handlers['textDocument/publishDiagnostics']
  vim.lsp.handlers['textDocument/publishDiagnostics'] = function (...)
    vim.cmd([[
      if !g:lsp_wait_done
        call airline#remove_statusline_func('LspWait')
        call airline#update_statusline()
        let g:lsp_wait_done = 1
      endif
    ]])
    if handler ~= nil then
      handler(...)
    end
  end
end

lspconfig['tsserver'].setup({
  capabilities = capabilities,
  on_attach = on_attach
})