init.lua/after/plugin/lsp.lua

-- setting error signs
local function sign_define(args)
	vim.fn.sign_define(args.name, {
		texthl = args.name,
		text = args.text,
		numhl = "",
	})
end

sign_define({ name = "DiagnosticSignError", text = "E" })
sign_define({ name = "DiagnosticSignWarn", text = "W" })
sign_define({ name = "DiagnosticSignHint", text = "H" })
sign_define({ name = "DiagnosticSignInfo", text = "I" })

-- diagnostic's aren't lsp dependent
vim.keymap.set("n", "<leader>vd", function()
	vim.diagnostic.open_float()
end)
vim.keymap.set("n", "[d", function()
	vim.diagnostic.goto_next()
end)
vim.keymap.set("n", "]d", function()
	vim.diagnostic.goto_prev()
end)

-- lsp capabilites enabler
vim.api.nvim_create_autocmd("LspAttach", {
	desc = "LSP Actions",
	callback = function(event)
		-- Enable omnifunc
		-- vim.bo[event.buf].omnifunc = "v:lua.vim.lsp.omnifunc"

		-- Buffer local mappings
		local opts = { buffer = event.buf }
		vim.keymap.set("n", "K", function()
			vim.lsp.buf.hover()
		end, opts)
		vim.keymap.set("n", "gd", function()
			vim.lsp.buf.definition()
		end, opts)
		vim.keymap.set("n", "gD", function()
			vim.lsp.buf.declaration()
		end, opts)
		vim.keymap.set("n", "gi", function()
			vim.lsp.buf.implementation()
		end, opts)
		vim.keymap.set("n", "<leader>lca", function()
			vim.lsp.buf.code_action()
		end, opts)
		vim.keymap.set("n", "<leader>lrn", function()
			vim.lsp.buf.rename()
		end, opts)
		vim.keymap.set("i", "<C-h>", function()
			vim.lsp.buf.signature_help()
		end, opts)
	end,
})

local lsp_capabilities = require("cmp_nvim_lsp").default_capabilities()

local default_setup = function(server)
	require("lspconfig")[server].setup({
		capabilities = lsp_capabilities,
	})
end

-- setup mason and automatically install some language server's
require("mason").setup({})
require("mason-lspconfig").setup({
	ensure_installed = { "lua_ls", "jsonls", "bashls", "pyright", "marksman", "gopls", "clangd" },
	handlers = { default_setup },
})

-- setup haskell language server manually cause it doesn't work with mason for xmonad
require("lspconfig").hls.setup({ capabilities = lsp_capabilities })

-- simple completion setup with snippet support
local cmp = require("cmp")

cmp.setup({
	sources = {
		{ name = "nvim_lsp" },
		{ name = "snippy" },
		{ name = "path" },
	},
	mapping = cmp.mapping.preset.insert({
		["<C-l>"] = cmp.mapping.confirm({ select = false }),
		["<C-j>"] = cmp.mapping(function(fallback)
			if cmp.visible then
				cmp.select_next_item()
			else
				fallback()
			end
		end, { "i", "s" }),
		["<C-k>"] = cmp.mapping(function(fallback)
			if cmp.visible then
				cmp.select_prev_item()
			else
				fallback()
			end
		end, { "i", "s" }),
	}),
	snippet = {
		expand = function(args)
			require("snippy").expand_snippet(args.body)
		end,
	},
	formatting = {
		format = require("lspkind").cmp_format({
			mode = "symbol_text", -- show only symbol annotations
			maxwidth = 50, -- prevent the popup from showing more than provided characters
			ellipsis_char = "...", -- when popup menu exceed maxwidth, the truncated part would show ellipsis_char instead
		}),
	},
	enabled = function()
		-- disable completion in comments
		local context = require("cmp.config.context")
		return not context.in_treesitter_capture("comment") and not context.in_syntax_group("Comment")
	end,
})