Dynamic snippet expansions

[lervag]

Contributing guidelines

• I have read CODE_OF_CONDUCT.md

Module(s)

mini.snippets

Question

Is it possible to run a Lua function while expanding a snippet to achieve dynamic behaviour? E.g., I want to do something like this:

  {
    prefix = "fun",
    desc = "Regular function",
    body = {
      function()
        return "function! " .. autoload_name() .. "($2) abort"
      end,
      "  $3",
      "endfunction",
      "",
    },
  },

where autoload_name will give the current files "autoload prefix". E.g. it could output vimtex#foo#bar#$1 if I'm inside the file autoload/vimtex/foo/bar.vim.

Notice, if I were to inline the above function, i.e.

  {
    prefix = "fun",
    desc = "Regular function",
    body = {
      "function! " .. autoload_name() .. "($2) abort"
      "  $3",
      "endfunction",
      "",
    },
  },

then the snippet expansion will not change when I change the file.

[echasnovski]

Yes, it is possible because entries in config.snippets can be function loaders. So this requires creating a local function (not possible to put that in a separate file, I am afraid) and use it inside require('mini.snippets').setup() as part of config.snippets.

Here is an example:

local vim_autoload_snippet = function(context)
  local buf_name = vim.api.nvim_buf_get_name(context.buf_id)
  local autoload_suffix = buf_name:match('autoload[\\/](.+)%.vim$')
  if autoload_suffix == nil then return {} end

  local autoload_name = autoload_suffix:gsub('[\\/]', '#')

  return {
    {
      prefix = 'fun',
      desc = 'Regular function',
      body = {
        'function! ' .. autoload_name .. '#$1($2) abort',
        -- I'd suggest using here `$0` tabstop directly
        '  $0',
        'endfunction',
        '',
      },
    },
  }
end

local minisnippets = require('mini.snippets')
minisnippets.setup({
  snippets = {
    -- Other snippet loaders go here
    vim_autoload_snippet,
  },
})

[echasnovski]

So, does this mean that if I create my own snippets e.g. in ~/.config/nvim/snippets/vim.lua, then I can let some of the snippets be functions instead of tables, where the functions need to return a snippet table?

In theory - yes. In practice - read_file() doesn't support callable values and I am not sure why... I'll take a closer look and maybe update it. Plus maybe add a note about "dynamic snippets" to general advice about management.

[lervag]

That sounds good. I just migrated from my 10+ year old Ultisnips setup, and I think dynamic snippets are the one thing I will miss if it is not available. The variable interpolation is sufficient in 90% of the cases, but some times I think the ability to generate the body at call time is very useful.

I realize it is possible with the custom loader, but I think it would be much better with regard to usabliity if it was possible to either allow the body to be a function that returns a string or list of strings, or let the entire snippet be a function that returns a table.

[echasnovski]

... or let the entire snippet be a function that returns a table.

Yes, this is already possible, as stated before. Even from custom Lua file, which returns an array of snippets: each either snippet table, function, or array of those.

It is just that built-in gen)loader.from_file('path/to/file') does not currently support that (it checks for every array element to be a snippet table). I don't remember why it is the case and will take a closer look.

[echasnovski]

read_file() should now work with functions as returned item. So something like this is now possible:

• Create a file '~/.config/nvim/snippets/vim-autoload.lua' with the following content:

  local autoload_snippet = function(context)
    local buf_id = context.buf_id
    -- ...
  end
  
  return { autoload_snippet }

• Use the following setup:

  local snippets, config_path = require('mini.snippets'), vim.fn.stdpath('config')
  snippets.setup({
    snippets = {
      snippets.gen_loader.from_file(config_path .. '/snippets/vim-autoload.lua'),
      -- The rest of the snippets
    },
  })

[lervag]

Great, this works very well - thanks for the quick update!