Avoid conflicts between denols and tsserver in Neovim

Recently I've been working on a project in a monorepo were I've got nodejs/typescript and deno projects. This is notoriously annoying because any ts file will start both tsserver and denols language services.

If you've got here you know what I'm talking about 😓

I'm setting up my lsp with lspconfig.

This is how denols is configured

lspconfig.denols.setup({
  root_dir = lspconfig.util.root_pattern("deno.json", "deno.jsonc"),
  init_options = {
    lint = true,
    unstable = true,
    suggest = {
      imports = {
        hosts = {
          ["https://deno.land"] = true,
          ["https://cdn.nest.land"] = true,
          ["https://crux.land"] = true,
        },
      },
    },
  },

  on_attach = on_attach,
})

And this is the hack to avoid tsserver to start on a file that belongs to a deno project.

spconfig.tsserver.setup({
  on_attach = function (client, bufnr)
    on_attach(client, bufnr);
    vim.keymap.set('n', '<leader>ro', function()
      vim.lsp.buf.execute_command({
        command = "_typescript.organizeImports",
        arguments = { vim.fn.expand("%:p") }
      })
    end, { buffer = bufnr,  remap = false });
  end,
  root_dir = function (filename, bufnr)
    local denoRootDir = lspconfig.util.root_pattern("deno.json", "deno.json")(filename);
    if denoRootDir then
      -- print('this seems to be a deno project; returning nil so that tsserver does not attach');
      return nil;
    -- else
      -- print('this seems to be a ts project; return root dir based on package.json')
    end

    return lspconfig.util.root_pattern("package.json")(filename);
  end,
  single_file_support = false,
})

This leverage the fact that if root_dir function returns nil then lspconfig wont's start a language service for that file. 🎉