nvim/lua/core/lsp/completion.lua

-- My neovim autocomplete setup.
-- partially stolen from https://github.com/glepnir/nvim
--
-- To make this work nicely you're gonna want a solid snippet setup, for me this
-- is luasnip. If you too would like to use luasnip just set vim.snippet.expand
-- to luasnip.lsp_expand

--- add char to list of triggerable chars
---@param list table list of chars
---@param char number|string char to add
local function add_to_client(list, char)
	local c

	if type(char) == "string" then
		c = char
	elseif type(char) == "number" then
		c = string.char(char)
	end
	if not table.contains(list, c) then
		table.insert(list, c)
	end
end

-- make sure we can add autos
local misc = require("core.misc")
local auto = misc.auto
local completion_group = misc.augroup("lsp.completion")

-- Configure the lsp completion menu. In addition to setting up lsp completion
-- this also styles it to look nice.
auto("LspAttach", {
	group = completion_group,
	callback = function(ctx)
		local client = vim.lsp.get_client_by_id(ctx.data.client_id)
		if not client or not client:supports_method("textDocument/completion") then
			return
		end

		-- Make completion menu appear whenever you type something.
		local c = client.server_capabilities.completionProvider.triggerCharacters
		if c then
			for i = 32, 126 do
				add_to_client(c, string.char(i))
			end
		end

		vim.lsp.completion.enable(true, client.id, ctx.buf, {
			autotrigger = true,
			convert = function(item)
        local kind = vim.lsp.protocol.CompletionItemKind[item.kind] or 'u'
        return {
					-- in the future if we ever get the ability to highlight specific
					-- entries in the pummenu I'd like to add treesitter highlighting to
					-- the entries
          abbr = item.label:gsub('%b()', ''),
          kind = kind:sub(1, 1):lower(),
          menu = ''
        }
			end
		})
	end
})

-- attempt to style the completion documentation popup
auto("CompleteChanged", {
	group = completion_group,
	callback = function()
		local info = vim.fn.complete_info({ "selected" })
		if info.preview_bufnr and vim.bo[info.preview_bufnr].filetype == "" then
			vim.bo[info.preview_bufnr].filetype = "markdown"
			vim.wo[info.preview_winid].conceallevel = 2
			vim.wo[info.preview_winid].concealcursor = "niv"
		end
	end
})

-- Add snippet support to lsp clients who don't do it for us. Currently this
-- only supports function calls.
--
-- there's a very good chance this will give us problems for languages who do
-- not follow the c-style function call style. I've only gotten this working in
-- lua thus far.
auto("CompleteDonePre", {
	group = completion_group,
	callback = function()
		local item = vim.tbl_get(
			vim.v.completed_item,
			"user_data",
			"nvim",
			"lsp",
			"completion_item"
		)
		if not item then
			return
		end

		-- if the item isn't a snippet then we might want to create a snippet
		if item.label and item.kind and item.insertTextFormat then
			if item.insertTextFormat ~= 2 and item.kind == 3 then
				local n_complete_item = vim.v.completed_item

				-- attempt to modify the function args to create a snippet
				local paren1 = string.find(item.label, "%(")
				if not paren1 then
					return
				end

				-- try and create a snippet from a function call
				local i = 1
				local text = ""
				local l_paren = paren1
				local next, is_paren
				while not is_paren do
					-- find the next token
					next = string.find(item.label, "%,", l_paren + 1)
					if not next then
						next = string.find(item.label, "%)", l_paren + 1)
						if not next then
							return
						end
						is_paren = true
					end

					-- concat text
					if text == "" then
						-- start the snippet
						text = string.sub(item.label, 0, l_paren).."${"..i..":"
					else
						-- continue the snippet
						text = text.."}, ".."${"..i..":"
					end

					do -- add the content of the argument to the snippet
						-- we need to account for cases in which the developer uses spaces
						-- between their commas and code
						local is_space = string.sub(item.label, l_paren + 1, l_paren + 1)
						local plus = is_space == " " and 2 or 1

						text = text..string.sub(item.label, l_paren + plus, next - 1)
					end

					-- increment
					l_paren = next
					i = i + 1
				end
				-- end the snippet
				text = text.."})"

				n_complete_item.user_data.nvim.lsp.completion_item.insertText = text
				n_complete_item.user_data.nvim.lsp.completion_item.insertTextFormat = 2
				n_complete_item.user_data.nvim.lsp.completion_item.kind = 3
				vim.v.completed_item = n_complete_item
			end
		end
	end
})

-- show the signature help when inside a function call
auto("CompleteDone", {
	group = completion_group,
	callback = function(ctx)
		-- make sure there's an lsp client, and make sure the lsp client supports
		-- textDocument/signatureHelp
		local client = vim.lsp.get_clients({ bufnr = ctx.buf })[1]
		if not client or not client:supports_method("textDocument/signatureHelp") then
			return
		end

		-- show the signature help
		local item = vim.tbl_get(
			vim.v.completed_item,
			"user_data",
			"nvim",
			"lsp",
			"completion_item"
		)
		if not item then
			return
		end

		-- show signature help when the completion is a function
		if item.kind == 3 and (item.textEdit ~= nil or item.insertText ~= nil) then
			-- for some reason calling vim.schedule didn't work for me
			vim.defer_fn(vim.lsp.buf.signature_help, 100)
		end
	end,
	desc = "Auto show signature help when completion is done"
})