Useful functions to explore Lua objects

Originally posted on Reddit

To look at contents of Lua object a you can execute :lua print(vim.inspect(a)). This will print content inside command line. Following nvim-lua-guide’s tip (edit: after making PR to nvim-lua-guide, it is currently in sync with edited version of this post), this can be wrapped into _G.dump() function and become :lua dump(a) (and even :lua dump(a, b)). However, in most cases it doesn’t print nil, which is a shame. This can be solved by sticking with single argument instead of ..., but it proved useful in certain cases. So I came up with alternative implementation and decided to share with everyone (edit: renamed previous dump for a somewhat more pleasant name):

function _G.put(...)
  local objects = {}
  for i = 1, select('#', ...) do
    local v = select(i, ...)
    table.insert(objects, vim.inspect(v))
  end

  print(table.concat(objects, '\n'))
  return ...
end

Now :lua put(nil) will actually print nil instead of just doing nothing. Also :lua put(nil, 1, nil) will print nil, 1, nil on separate lines (instead of nil 1).

But there is more. Sometimes you want to explore a big nested table (like LSP related stuff). It would be nicer to explore as regular text. And so put_text() was born:

function _G.put_text(...)
  local objects = {}
  for i = 1, select('#', ...) do
    local v = select(i, ...)
    table.insert(objects, vim.inspect(v))
  end

  local lines = vim.split(table.concat(objects, '\n'), '\n')
  local lnum = vim.api.nvim_win_get_cursor(0)[1]
  vim.fn.append(lnum, lines)
  return ...
end

When called, this will try to add inspection content under the current cursor position. So now if you want to conveniently explore all fields of vim.loop, just execute :lua put_text(vim.loop).

Hope this will help somebody.

P.S.: To use put() and put_text() inside Neovim session, you need to source this Lua code. Easiest way is to put it inside Lua files sourced on startup (‘init.lua’, for example), and you are good to go.