use {
  "benfowler/telescope-luasnip.nvim",
  module = "telescope._extensions.luasnip",  -- if you wish to lazy-load
}

require('telescope').load_extension('luasnip')

require'telescope'.extensions.luasnip.luasnip{}
vim.cmd [[ Telescope luasnip ]]

local lst = require('telescope').extensions.luasnip
local luasnip = require('luasnip')
require('telescope').setup {
  extensions = {
    -- ...
    luasnip = {
      search = function(entry)
        return lst.filter_null(entry.context.trigger) .. " " ..
               lst.filter_null(entry.context.name) .. " " ..
               entry.ft .. " " ..
               lst.filter_description(entry.context.name, entry.context.description) ..
               lst.get_docstring(luasnip, entry.ft, entry.context)[1]
      end
    },
     -- ...
  }
}

require('telescope').setup {
  luasnip = require("telescope.themes".get_dropdown({
      border   = false,
      preview  = {
        check_mime_type  = true
      },
      search = function ()
        -- ...
      end
    }))
}