Is possible to create a snippet that when expanded it insert a line in the start of the file?

[LaBatata101]

I'm trying to create a snippet like this:

from dataclasses import dataclass

@dataclass
class {1}:
    {0}

When I type dataclass it would expand the snippet and insert the line from dataclasses import dataclass at the start of the file.
But I have no idea how to do this. Can someone help me?

[L3MON4D3]

Ouh, yeah that's possible: just create a functionNode without arg nodes. The code in there will only run once during the initial expansion and you won't see it as long as it doesn't return any text returns an empty string.

s("dataclass", {
    <other nodes>, 
    f(insert_dataclass_at_beginning, {})
})

This will be more straightforward once pre_expand/post_expand-callbacks are added.

[LaBatata101]

Cool! So I came up with this code:

ls.add_snippets("python", {
  s("dataclass", {
    t({ "@dataclass", "class " }),
    i(1),
    t({ ":", "\t" }),
    i(0),
    f(function(_, _)
      vim.api.nvim_buf_set_lines(0, 0, 0, true, { "from dataclasses import dataclass" })
      return ""
    end, {}),
  }),
})

But I'm getting this error when I try to expand the snippet:

E5108: Error executing lua ...e/nvim/site/pack/packer/opt/LuaSnip/lua/luasnip/init.lua:179: end_col out of bounds
stack traceback:
        [C]: in function 'nvim_buf_set_text'
        ...e/nvim/site/pack/packer/opt/LuaSnip/lua/luasnip/init.lua:179: in function 'snip_expand'
        ...e/nvim/site/pack/packer/opt/LuaSnip/lua/luasnip/init.lua:242: in function 'expand'
        ...e/nvim/site/pack/packer/opt/LuaSnip/lua/luasnip/init.lua:289: in function 'expand_or_jump'
        /home/labatata/.config/nvim/lua/config/plugins/cmp.lua:28: in function 'on_keymap'
        ...hare/nvim/site/pack/packer/opt/nvim-cmp/lua/cmp/core.lua:145: in function 'callback'
        ...m/site/pack/packer/opt/nvim-cmp/lua/cmp/utils/keymap.lua:114: in function <...m/site/pack/packer/opt/nvim-cmp/lua/cmp/utils/keymap.lua:108>
        ...m/site/pack/packer/opt/nvim-cmp/lua/cmp/utils/keymap.lua:244: in function <...m/site/pack/packer/opt/nvim-cmp/lua/cmp/utils/keymap.lua:243>

And it gets expanded wrong, the trigger text it's not getting removed:

dataclass@dataclass
class :

Not sure what I'm doing wrong.

[L3MON4D3]

Ofc🤦‍♂️: we store the position the trigger was at and clear it only after the snippet was expanded, if some text is inserted during expansion, it'll fail.
You can vim.schedule the insertion, that way it should work.

[LaBatata101]

Thanks, that worked!

[leiserfg]

Functions are evaluated withing the previews, I think better to use some kind of guard to avoid rewriting the line.

[L3MON4D3]

Oh right, thats also important, otherwise you'll get the text even when scrolling over the snippet via nvim-cmp (if documentation is enabled at least)

[LaBatata101]

Thanks for the info!