luasnip+treesitter snippet that fills in prop names when creating new react component

luasnip_config.lua

local ls = require("luasnip")
local fmt = require("luasnip.extras.fmt").fmt
local s = ls.snippet
local i = ls.insert_node
local f = ls.function_node
local d = ls.dynamic_node
local sn = ls.snippet_node
local rep = require("luasnip.extras").rep

-- Get a list of  the property names given an `interface_declaration`
-- treesitter *tsx* node.
-- Ie, if the treesitter node represents:
--   interface {
--     prop1: string;
--     prop2: number;
--   }
-- Then this function would return `{"prop1", "prop2"}
---@param id_node {} Stands for "interface declaration node"
---@return string[]
local function get_prop_names(id_node)
	local object_type_node = id_node:child(2)
	if object_type_node:type() ~= "object_type" then
		return {}
	end

	local prop_names = {}

	for prop_signature in object_type_node:iter_children() do
		if prop_signature:type() == "property_signature" then
			local prop_iden = prop_signature:child(0)
			local prop_name = vim.treesitter.query.get_node_text(prop_iden, 0)
			prop_names[#prop_names + 1] = prop_name
		end
	end

	return prop_names
end

ls.add_snippets("typescriptreact", {
	s(
		"c",
		fmt(
			[[
{}interface {}Props {{
  {}
}}

{}function {}({{{}}}: {}Props) {{
  {}
}}
]],
			{
				i(1, "export "),

                                -- Initialize component name to file name 
				d(2, function(_, snip)
					return sn(nil, {
						i(1, vim.fn.substitute(snip.env.TM_FILENAME, "\\..*$", "", "g")),
					})
				end, { 1 }),
				i(3, "// props"),
				rep(1),
				rep(2),
				f(function(_, snip, _)
					local pos_begin = snip.nodes[6].mark:pos_begin()
					local pos_end = snip.nodes[6].mark:pos_end()
					local parser = vim.treesitter.get_parser(0, "tsx")
					local tstree = parser:parse()

					local node = tstree[1]
						:root()
						:named_descendant_for_range(pos_begin[1], pos_begin[2], pos_end[1], pos_end[2])

					while node ~= nil and node:type() ~= "interface_declaration" do
						node = node:parent()
					end

					if node == nil then
						return ""
					end

					-- `node` is now surely of type "interface_declaration"
					local prop_names = get_prop_names(node)

					-- Does this lua->vimscript->lua thing cause a slow down? Dunno.
					return vim.fn.join(prop_names, ", ")
				end, { 3 }),
				rep(2),
				i(5, "return <div></div>"),
			}
		)
	),
})

This is genuinely embarrassing 😂! Thanks @Decodetalkers, it's fixed.