Function node that depends on the last insert node

[lacarthur]

Hello,
I'm trying to create a snippet that looks like this :
${insertnode 1}${insertnode 0}
for latex inline equations. However, I want to insert a space right before the last insert_node, unless the first character of the text after the equation does not require it : ' ', '.', ',', etc...
I've been trying to do this using a function node, but so far, it doesn't work. Here is what I have :

local function table_contains(table, element)
    for _, value in pairs(table) do
        if value == element then
            return true
        end
    end
    return false
end

local no_space_in_front = { ' ', ',', '.', '?', '-' }

local optional_space_node = function(insert_node_id)
    return function_node(function (args)
        if args[1][1] == '' then
            return 'nospace'
        end
        if table_contains(no_space_in_front, string.sub(args[1][1], 1, 1)) then
            return "nospace"
        else
            return "space"
        end
    end,
    insert_node_id)
end

ls.add_snippets("tex", {
    snippet({
        trig="mk",
        name="inline_math",
        dscr="An inline math formula.",
        wordTrig=true,
        regTrig=false,
        },
        {
            text_node("$"), insert_node(1), text_node("$"), optional_space_node(0), insert_node(0)
        }),
    },
    {type = "autosnippets",}
)

If I change the optional_space_node to target the insert_node 1, the snippet behaves as expected. But when I change it back to 0, I don't get anything : neither 'space' nor 'nospace'.
Am I going about this the right way?
Thank you.

[L3MON4D3]

This is pretty much correct, the problem is just that the i(0) is not really an insertNode, so luasnip cant find the node the fNode depends on, and therefore just does not run it :/ (there already are some issues about this which contain reasoning, I won't repeat that here).
I recall proposing a solution to a problem very similar to yours, could you try searching through old issues/discussions?
If you don't find anything I can look into this again :)

[lacarthur]

Ah, yes, my bad.
I hadn't checked the issues, someone was having the exact same problem in #293.
Here is my solution, adapted for nvim_create_autocmd :

snippet({
    trig="mk",
    name="inline_math",
    dscr="An inline math formula.",
    wordTrig=true,
    regTrig=false,
},
{
    text_node("$"), insert_node(1), text_node("$")
},
{
    callbacks = {
        [-1] = {
            [events.leave] = function()
                vim.api.nvim_create_autocmd("InsertCharPre", {
                    buffer = 0,
                    once = true,
                    callback = function ()
                        if not table_contains(no_space_in_front, vim.v.char) then
                            vim.v.char = " " .. vim.v.char
                        end
                    end
                })
            end
        }
    }
})

It is a bit convoluted, but it works fine. Thank you for the help.

[L3MON4D3]

Ah nice, that looks good 👍