refactor: fix luals warnings

17 files changed, 133 insertions, 77 deletions

diff --git a/.luarc.json b/.luarc.json
index 5a014a26ea..2bd57d6973 100644
--- a/.luarc.json
+++ b/.luarc.json
@@ -1,7 +1,7 @@
 {
   "$schema": "https://raw.githubusercontent.com/LuaLS/vscode-lua/master/setting/schema.json",
   "runtime": {
-      "version": "LuaJIT"
+    "version": "LuaJIT"
   },
   "workspace": {
     "library": [
@@ -12,7 +12,7 @@
     "ignoreDir": [
       "test"
     ],
-    "checkThirdParty": false
+    "checkThirdParty": "Disable"
   },
   "diagnostics": {
     "groupFileStatus": {
diff --git a/runtime/lua/vim/_editor.lua b/runtime/lua/vim/_editor.lua
index 0b338fa86f..cde61697b6 100644
--- a/runtime/lua/vim/_editor.lua
+++ b/runtime/lua/vim/_editor.lua
@@ -156,10 +156,10 @@ function vim._os_proc_info(pid)
   elseif r.code ~= 0 then
     error('command failed: ' .. vim.fn.string(cmd))
   end
-  local ppid = assert(vim.system({ 'ps', '-p', pid, '-o', 'ppid=' }):wait().stdout)
+  local ppid_string = assert(vim.system({ 'ps', '-p', pid, '-o', 'ppid=' }):wait().stdout)
   -- Remove trailing whitespace.
   name = vim.trim(name):gsub('^.*/', '')
-  ppid = tonumber(ppid) or -1
+  local ppid = tonumber(ppid_string) or -1
   return {
     name = name,
     pid = pid,
@@ -533,20 +533,21 @@ function vim.region(bufnr, pos1, pos2, regtype, inclusive)
 
   local region = {}
   for l = pos1[1], pos2[1] do
-    local c1, c2
+    local c1 --- @type number
+    local c2 --- @type number
     if regtype:byte() == 22 then -- block selection: take width from regtype
       c1 = pos1[2]
-      c2 = c1 + regtype:sub(2)
+      c2 = c1 + tonumber(regtype:sub(2))
       -- and adjust for non-ASCII characters
       local bufline = vim.api.nvim_buf_get_lines(bufnr, l, l + 1, true)[1]
       local utflen = vim.str_utfindex(bufline, #bufline)
       if c1 <= utflen then
-        c1 = vim.str_byteindex(bufline, c1)
+        c1 = assert(tonumber(vim.str_byteindex(bufline, c1)))
       else
         c1 = #bufline + 1
       end
       if c2 <= utflen then
-        c2 = vim.str_byteindex(bufline, c2)
+        c2 = assert(tonumber(vim.str_byteindex(bufline, c2)))
       else
         c2 = #bufline + 1
       end
@@ -576,7 +577,7 @@ end
 ---@return table timer luv timer object
 function vim.defer_fn(fn, timeout)
   vim.validate({ fn = { fn, 'c', true } })
-  local timer = vim.uv.new_timer()
+  local timer = assert(vim.uv.new_timer())
   timer:start(
     timeout,
     0,
@@ -601,6 +602,7 @@ end
 ---@param msg string Content of the notification to show to the user.
 ---@param level integer|nil One of the values from |vim.log.levels|.
 ---@param opts table|nil Optional parameters. Unused by default.
+---@diagnostic disable-next-line: unused-local
 function vim.notify(msg, level, opts) -- luacheck: no unused args
   if level == vim.log.levels.ERROR then
     vim.api.nvim_err_writeln(msg)
@@ -700,6 +702,8 @@ end
 ---
 ---     1. Can we get it to just return things in the global namespace with that name prefix
 ---     2. Can we get it to return things from global namespace even with `print(` in front.
+---
+--- @param pat string
 function vim._expand_pat(pat, env)
   env = env or _G
 
@@ -801,11 +805,13 @@ function vim._expand_pat(pat, env)
   return keys, #prefix_match_pat
 end
 
+--- @param lua_string string
 vim._expand_pat_get_parts = function(lua_string)
   local parts = {}
 
   local accumulator, search_index = '', 1
-  local in_brackets, bracket_end = false, -1
+  local in_brackets = false
+  local bracket_end = -1 --- @type integer?
   local string_char = nil
   for idx = 1, #lua_string do
     local s = lua_string:sub(idx, idx)
@@ -938,9 +944,12 @@ function vim.keycode(str)
   return vim.api.nvim_replace_termcodes(str, true, true, true)
 end
 
+--- @param server_addr string
+--- @param connect_error string
 function vim._cs_remote(rcid, server_addr, connect_error, args)
+  --- @return string
   local function connection_failure_errmsg(consequence)
-    local explanation
+    local explanation --- @type string
     if server_addr == '' then
       explanation = 'No server specified with --server'
     else
@@ -983,7 +992,7 @@ function vim._cs_remote(rcid, server_addr, connect_error, args)
     local res = tostring(vim.rpcrequest(rcid, 'nvim_eval', args[2]))
     return { result = res, should_exit = true, tabbed = false }
   elseif subcmd ~= '' then
-    return { errmsg = 'Unknown option argument: ' .. args[1] }
+    return { errmsg = 'Unknown option argument: ' .. tostring(args[1]) }
   end
 
   if rcid == 0 then
diff --git a/runtime/lua/vim/_init_packages.lua b/runtime/lua/vim/_init_packages.lua
index f8710f7fd7..97d483333e 100644
--- a/runtime/lua/vim/_init_packages.lua
+++ b/runtime/lua/vim/_init_packages.lua
@@ -12,6 +12,7 @@ for s in (package.cpath .. ';'):gmatch('[^;]*;') do
   end
 end
 
+--- @param name string
 function vim._load_package(name)
   local basename = name:gsub('%.', '/')
   local paths = { 'lua/' .. basename .. '.lua', 'lua/' .. basename .. '/init.lua' }
diff --git a/runtime/lua/vim/_watch.lua b/runtime/lua/vim/_watch.lua
index 43fce3bf7f..092781826f 100644
--- a/runtime/lua/vim/_watch.lua
+++ b/runtime/lua/vim/_watch.lua
@@ -51,6 +51,7 @@ function M.watch(path, opts, callback)
   local uvflags = opts and opts.uvflags or {}
   local handle, new_err = vim.uv.new_fs_event()
   assert(not new_err, new_err)
+  handle = assert(handle)
   local _, start_err = handle:start(path, uvflags, function(err, filename, events)
     assert(not err, err)
     local fullpath = path
diff --git a/runtime/lua/vim/diagnostic.lua b/runtime/lua/vim/diagnostic.lua
index a82a61eeb7..ad40723737 100644
--- a/runtime/lua/vim/diagnostic.lua
+++ b/runtime/lua/vim/diagnostic.lua
@@ -108,6 +108,7 @@ local function filter_by_severity(severity, diagnostics)
     severities[to_severity(s)] = true
   end
 
+  --- @param t table
   return vim.tbl_filter(function(t)
     return severities[t.severity]
   end, diagnostics)
diff --git a/runtime/lua/vim/health.lua b/runtime/lua/vim/health.lua
index 23771d2807..55a451bf56 100644
--- a/runtime/lua/vim/health.lua
+++ b/runtime/lua/vim/health.lua
@@ -1,8 +1,8 @@
 local M = {}
 
-local s_output = {}
+local s_output = {} ---@type string[]
 
--- Returns the fold text of the current healthcheck section
+--- Returns the fold text of the current healthcheck section
 function M.foldtext()
   local foldtext = vim.fn.foldtext()
 
@@ -36,12 +36,13 @@ function M.foldtext()
   return vim.b.failedchecks[foldtext] and '+WE' .. foldtext:sub(4) or foldtext
 end
 
--- From a path return a list [{name}, {func}, {type}] representing a healthcheck
+--- @param path string path to search for the healthcheck
+--- @return string[] { name, func, type } representing a healthcheck
 local function filepath_to_healthcheck(path)
   path = vim.fs.normalize(path)
-  local name
-  local func
-  local filetype
+  local name --- @type string
+  local func --- @type string
+  local filetype --- @type string
   if path:find('vim$') then
     name = vim.fs.basename(path):gsub('%.vim$', '')
     func = 'health#' .. name .. '#check'
@@ -50,10 +51,10 @@ local function filepath_to_healthcheck(path)
     local subpath = path:gsub('.*lua/', '')
     if vim.fs.basename(subpath) == 'health.lua' then
       -- */health.lua
-      name = vim.fs.dirname(subpath)
+      name = assert(vim.fs.dirname(subpath))
     else
       -- */health/init.lua
-      name = vim.fs.dirname(vim.fs.dirname(subpath))
+      name = assert(vim.fs.dirname(assert(vim.fs.dirname(subpath))))
     end
     name = name:gsub('/', '.')
 
@@ -63,11 +64,12 @@ local function filepath_to_healthcheck(path)
   return { name, func, filetype }
 end
 
--- Returns { {name, func, type}, ... } representing healthchecks
+--- @param plugin_names string
+--- @return table<any,string[]> { {name, func, type}, ... } representing healthchecks
 local function get_healthcheck_list(plugin_names)
-  local healthchecks = {}
-  plugin_names = vim.split(plugin_names, ' ')
-  for _, p in pairs(plugin_names) do
+  local healthchecks = {} --- @type table<any,string[]>
+  local plugin_names_list = vim.split(plugin_names, ' ')
+  for _, p in pairs(plugin_names_list) do
     -- support vim/lsp/health{/init/}.lua as :checkhealth vim.lsp
 
     p = p:gsub('%.', '/')
@@ -83,7 +85,7 @@ local function get_healthcheck_list(plugin_names)
     if vim.tbl_count(paths) == 0 then
       healthchecks[#healthchecks + 1] = { p, '', '' } -- healthcheck not found
     else
-      local unique_paths = {}
+      local unique_paths = {} --- @type table<string, boolean>
       for _, v in pairs(paths) do
         unique_paths[v] = true
       end
@@ -100,10 +102,11 @@ local function get_healthcheck_list(plugin_names)
   return healthchecks
 end
 
--- Returns {name: [func, type], ..} representing healthchecks
+--- @param plugin_names string
+--- @return table<string, string[]> {name: [func, type], ..} representing healthchecks
 local function get_healthcheck(plugin_names)
   local health_list = get_healthcheck_list(plugin_names)
-  local healthchecks = {}
+  local healthchecks = {} --- @type table<string, string[]>
   for _, c in pairs(health_list) do
     if c[1] ~= 'vim' then
       healthchecks[c[1]] = { c[2], c[3] }
@@ -113,7 +116,11 @@ local function get_healthcheck(plugin_names)
   return healthchecks
 end
 
--- Indents lines *except* line 1 of a string if it contains newlines.
+--- Indents lines *except* line 1 of a string if it contains newlines.
+---
+--- @param s string
+--- @param columns integer
+--- @return string
 local function indent_after_line1(s, columns)
   local lines = vim.split(s, '\n')
   local indent = string.rep(' ', columns)
@@ -123,13 +130,20 @@ local function indent_after_line1(s, columns)
   return table.concat(lines, '\n')
 end
 
--- Changes ':h clipboard' to ':help |clipboard|'.
+--- Changes ':h clipboard' to ':help |clipboard|'.
+---
+--- @param s string
+--- @return string
 local function help_to_link(s)
   return vim.fn.substitute(s, [[\v:h%[elp] ([^|][^"\r\n ]+)]], [[:help |\1|]], [[g]])
 end
 
--- Format a message for a specific report item.
--- Variable args: Optional advice (string or list)
+--- Format a message for a specific report item.
+---
+--- @param status string
+--- @param msg string
+--- @param ... string|string[] Optional advice
+--- @return string
 local function format_report_message(status, msg, ...)
   local output = '- ' .. status
   if status ~= '' then
@@ -159,42 +173,54 @@ local function format_report_message(status, msg, ...)
   return help_to_link(output)
 end
 
+--- @param output string
 local function collect_output(output)
   vim.list_extend(s_output, vim.split(output, '\n'))
 end
 
--- Starts a new report.
+--- Starts a new report.
+---
+--- @param name string
 function M.start(name)
   local input = string.format('\n%s ~', name)
   collect_output(input)
 end
 
--- Reports a message in the current section.
+--- Reports a message in the current section.
+---
+--- @param msg string
 function M.info(msg)
   local input = format_report_message('', msg)
   collect_output(input)
 end
 
--- Reports a successful healthcheck.
+--- Reports a successful healthcheck.
+---
+--- @param msg string
 function M.ok(msg)
   local input = format_report_message('OK', msg)
   collect_output(input)
 end
 
--- Reports a health warning.
--- ...: Optional advice (string or table)
+--- Reports a health warning.
+---
+--- @param msg string
+--- @param ... string|string[] Optional advice
 function M.warn(msg, ...)
   local input = format_report_message('WARNING', msg, ...)
   collect_output(input)
 end
 
--- Reports a failed healthcheck.
--- ...: Optional advice (string or table)
+--- Reports a failed healthcheck.
+---
+--- @param msg string
+--- @param ... string|string[] Optional advice
 function M.error(msg, ...)
   local input = format_report_message('ERROR', msg, ...)
   collect_output(input)
 end
 
+--- @param type string
 local function deprecate(type)
   local before = string.format('vim.health.report_%s()', type)
   local after = string.format('vim.health.%s()', type)
@@ -206,22 +232,36 @@ local function deprecate(type)
   vim.print('Running healthchecks...')
 end
 
+--- @deprecated
+--- @param name string
 function M.report_start(name)
   deprecate('start')
   M.start(name)
 end
+
+--- @deprecated
+--- @param msg string
 function M.report_info(msg)
   deprecate('info')
   M.info(msg)
 end
+
+--- @deprecated
+--- @param msg string
 function M.report_ok(msg)
   deprecate('ok')
   M.ok(msg)
 end
+
+--- @deprecated
+--- @param msg string
 function M.report_warn(msg, ...)
   deprecate('warn')
   M.warn(msg, ...)
 end
+
+--- @deprecated
+--- @param msg string
 function M.report_error(msg, ...)
   deprecate('error')
   M.error(msg, ...)
@@ -251,7 +291,7 @@ local path2name = function(path)
 end
 
 local PATTERNS = { '/autoload/health/*.vim', '/lua/**/**/health.lua', '/lua/**/**/health/init.lua' }
--- :checkhealth completion function used by cmdexpand.c get_healthcheck_names()
+--- :checkhealth completion function used by cmdexpand.c get_healthcheck_names()
 M._complete = function()
   local names = vim.tbl_flatten(vim.tbl_map(function(pattern)
     return vim.tbl_map(path2name, vim.api.nvim_get_runtime_file(pattern, true))
@@ -270,6 +310,9 @@ end
 --- Runs all discovered healthchecks if plugin_names is empty.
 ---
 --- @param mods string command modifiers that affect splitting a window.
+--- @param plugin_names string glob of plugin names, split on whitespace. For example, using
+---                            `:checkhealth vim.* nvim` will healthcheck `vim.lsp`, `vim.treesitter`
+---                            and `nvim` modules.
 function M._check(mods, plugin_names)
   local healthchecks = plugin_names == '' and get_healthcheck('*') or get_healthcheck(plugin_names)
 
@@ -289,7 +332,8 @@ function M._check(mods, plugin_names)
   vim.cmd.file('health://')
   vim.cmd.setfiletype('checkhealth')
 
-  if healthchecks == nil or next(healthchecks) == nil then
+  -- This should only happen when doing `:checkhealth vim`
+  if next(healthchecks) == nil then
     vim.fn.setline(1, 'ERROR: No healthchecks found.')
     return
   end
@@ -325,7 +369,7 @@ function M._check(mods, plugin_names)
     local header = { string.rep('=', 78), name .. ': ' .. func, '' }
     -- remove empty line after header from report_start
     if s_output[1] == '' then
-      local tmp = {}
+      local tmp = {} ---@type string[]
       for i = 2, #s_output do
         tmp[#tmp + 1] = s_output[i]
       end
diff --git a/runtime/lua/vim/iter.lua b/runtime/lua/vim/iter.lua
index 8e602c406a..b658dde099 100644
--- a/runtime/lua/vim/iter.lua
+++ b/runtime/lua/vim/iter.lua
@@ -432,6 +432,7 @@ end
 --- ```
 ---
 ---@return any
+---@diagnostic disable-next-line: unused-local
 function Iter.next(self) -- luacheck: no unused args
   -- This function is provided by the source iterator in Iter.new. This definition exists only for
   -- the docstring
@@ -489,6 +490,7 @@ end
 --- ```
 ---
 ---@return any
+---@diagnostic disable-next-line: unused-local
 function Iter.peek(self) -- luacheck: no unused args
   error('peek() requires a list-like table')
 end
@@ -568,12 +570,13 @@ end
 ---@see Iter.find
 ---
 ---@return any
+---@diagnostic disable-next-line: unused-local
 function Iter.rfind(self, f) -- luacheck: no unused args
   error('rfind() requires a list-like table')
 end
 
 ---@private
-function ListIter.rfind(self, f) -- luacheck: no unused args
+function ListIter.rfind(self, f)
   if type(f) ~= 'function' then
     local val = f
     f = function(v)
@@ -640,6 +643,7 @@ end
 --- ```
 ---
 ---@return any
+---@diagnostic disable-next-line: unused-local
 function Iter.nextback(self) -- luacheck: no unused args
   error('nextback() requires a list-like table')
 end
@@ -669,6 +673,7 @@ end
 --- ```
 ---
 ---@return any
+---@diagnostic disable-next-line: unused-local
 function Iter.peekback(self) -- luacheck: no unused args
   error('peekback() requires a list-like table')
 end
@@ -725,6 +730,7 @@ end
 ---
 ---@param n number Number of values to skip.
 ---@return Iter
+---@diagnostic disable-next-line: unused-local
 function Iter.skipback(self, n) -- luacheck: no unused args
   error('skipback() requires a list-like table')
   return self
@@ -791,6 +797,7 @@ end
 ---@param first number
 ---@param last number
 ---@return Iter
+---@diagnostic disable-next-line: unused-local
 function Iter.slice(self, first, last) -- luacheck: no unused args
   error('slice() requires a list-like table')
   return self
diff --git a/runtime/lua/vim/loader.lua b/runtime/lua/vim/loader.lua
index ee01111337..b77251cf7e 100644
--- a/runtime/lua/vim/loader.lua
+++ b/runtime/lua/vim/loader.lua
@@ -1,5 +1,5 @@
 local uv = vim.uv
-local uri_encode = vim.uri_encode
+local uri_encode = vim.uri_encode --- @type function
 
 --- @type (fun(modename: string): fun()|string)[]
 local loaders = package.loaders
diff --git a/runtime/lua/vim/lsp.lua b/runtime/lua/vim/lsp.lua
index 1310239a5b..3105413b53 100644
--- a/runtime/lua/vim/lsp.lua
+++ b/runtime/lua/vim/lsp.lua
@@ -329,11 +329,11 @@ end
 ---@param fn (T) Function to run
 ---@return T
 local function once(fn)
-  local value --- @type any
+  local value --- @type function
   local ran = false
   return function(...)
     if not ran then
-      value = fn(...)
+      value = fn(...) --- @type function
       ran = true
     end
     return value
diff --git a/runtime/lua/vim/lsp/buf.lua b/runtime/lua/vim/lsp/buf.lua
index 051b9d4550..d67b2ac8ea 100644
--- a/runtime/lua/vim/lsp/buf.lua
+++ b/runtime/lua/vim/lsp/buf.lua
@@ -46,7 +46,7 @@ function M.hover()
 end
 
 local function request_with_options(name, params, options)
-  local req_handler
+  local req_handler --- @type function?
   if options then
     req_handler = function(err, result, ctx, config)
       local client = assert(vim.lsp.get_client_by_id(ctx.client_id))
diff --git a/runtime/lua/vim/shared.lua b/runtime/lua/vim/shared.lua
index 9542d93789..bbbc888727 100644
--- a/runtime/lua/vim/shared.lua
+++ b/runtime/lua/vim/shared.lua
@@ -617,11 +617,6 @@ function vim.tbl_islist(t)
   local num_elem = vim.tbl_count(t)
 
   if num_elem == 0 then
-    -- TODO(bfredl): in the future, we will always be inside nvim
-    -- then this check can be deleted.
-    if vim._empty_dict_mt == nil then
-      return nil
-    end
     return getmetatable(t) ~= vim._empty_dict_mt
   else
     for i = 1, num_elem do
diff --git a/runtime/lua/vim/ui.lua b/runtime/lua/vim/ui.lua
index b6ddf337ce..25ced18daf 100644
--- a/runtime/lua/vim/ui.lua
+++ b/runtime/lua/vim/ui.lua
@@ -133,7 +133,7 @@ function M.open(path)
     path = vim.fn.expand(path)
   end
 
-  local cmd
+  local cmd --- @type string[]
 
   if vim.fn.has('mac') == 1 then
     cmd = { 'open', path }
diff --git a/test/.luarc.json b/test/.luarc.json
index 5d19a37266..1de363557d 100644
--- a/test/.luarc.json
+++ b/test/.luarc.json
@@ -12,7 +12,7 @@
       "${3rd}/luassert/library",
       "${3rd}/luv/library"
     ],
-    "checkThirdParty": false
+    "checkThirdParty": "Disable"
   },
   "diagnostics": {
     "groupFileStatus": {
diff --git a/test/functional/helpers.lua b/test/functional/helpers.lua
index 2e1f196226..a852e8cc08 100644
--- a/test/functional/helpers.lua
+++ b/test/functional/helpers.lua
@@ -65,10 +65,7 @@ if os.getenv('VALGRIND') then
     table.insert(prepend_argv, '--vgdb-error=0')
   end
 elseif os.getenv('GDB') then
-  local gdbserver_port = '7777'
-  if os.getenv('GDBSERVER_PORT') then
-    gdbserver_port = os.getenv('GDBSERVER_PORT')
-  end
+  local gdbserver_port = os.getenv('GDBSERVER_PORT') or '7777'
   prepend_argv = {'gdbserver', 'localhost:'..gdbserver_port}
 end
 
diff --git a/test/functional/ui/screen.lua b/test/functional/ui/screen.lua
index 99cf4ffb1b..096d8a27fb 100644
--- a/test/functional/ui/screen.lua
+++ b/test/functional/ui/screen.lua
@@ -1593,6 +1593,7 @@ function Screen:_pprint_attrs(attrs, cterm)
     return table.concat(items, ", ")
 end
 
+---@diagnostic disable-next-line: unused-local, unused-function
 local function backward_find_meaningful(tbl, from)  -- luacheck: no unused
   for i = from or #tbl, 1, -1 do
     if tbl[i] ~= ' ' then
diff --git a/test/helpers.lua b/test/helpers.lua
index 0ced3ec163..83f87c856b 100644
--- a/test/helpers.lua
+++ b/test/helpers.lua
@@ -1,10 +1,10 @@
 local shared = vim
-local assert = require('luassert')
+local luaassert = require('luassert')
 local busted = require('busted')
 local luv = require('luv')
 local Paths = require('test.cmakeconfig.paths')
 
-assert:set_parameter('TableFormatLevel', 100)
+luaassert:set_parameter('TableFormatLevel', 100)
 
 local quote_me = '[^.%w%+%-%@%_%/]' -- complement (needn't quote)
 local function shell_quote(str)
@@ -82,8 +82,8 @@ end
 -- Calls fn() until it succeeds, up to `max` times or until `max_ms`
 -- milliseconds have passed.
 function module.retry(max, max_ms, fn)
-  assert(max == nil or max > 0)
-  assert(max_ms == nil or max_ms > 0)
+  luaassert(max == nil or max > 0)
+  luaassert(max_ms == nil or max_ms > 0)
   local tries = 1
   local timeout = (max_ms and max_ms or 10000)
   local start_time = luv.now()
@@ -108,10 +108,10 @@ local check_logs_useless_lines = {
 }
 
 function module.eq(expected, actual, context)
-  return assert.are.same(expected, actual, context)
+  return luaassert.are.same(expected, actual, context)
 end
 function module.neq(expected, actual, context)
-  return assert.are_not.same(expected, actual, context)
+  return luaassert.are_not.same(expected, actual, context)
 end
 
 --- Asserts that `cond` is true, or prints a message.
@@ -120,21 +120,21 @@ end
 --- @param expected (any) description of expected result
 --- @param actual (any) description of actual result
 function module.ok(cond, expected, actual)
-  assert(
+  luaassert(
     (not expected and not actual) or (expected and actual),
     'if "expected" is given, "actual" is also required'
   )
   local msg = expected and ('expected %s, got: %s'):format(expected, tostring(actual)) or nil
-  return assert(cond, msg)
+  return luaassert(cond, msg)
 end
 
 local function epicfail(state, arguments, _)
   state.failure_message = arguments[1]
   return false
 end
-assert:register('assertion', 'epicfail', epicfail)
+luaassert:register('assertion', 'epicfail', epicfail)
 function module.fail(msg)
-  return assert.epicfail(msg)
+  return luaassert.epicfail(msg)
 end
 
 function module.matches(pat, actual)
@@ -154,7 +154,7 @@ end
 ---@param inverse? (boolean) Assert that the pattern does NOT match.
 function module.assert_log(pat, logfile, nrlines, inverse)
   logfile = logfile or os.getenv('NVIM_LOG_FILE') or '.nvimlog'
-  assert(logfile ~= nil, 'no logfile')
+  luaassert(logfile ~= nil, 'no logfile')
   nrlines = nrlines or 10
   inverse = inverse or false
 
@@ -191,7 +191,7 @@ function module.assert_nolog(pat, logfile, nrlines)
 end
 
 function module.pcall(fn, ...)
-  assert(type(fn) == 'function')
+  luaassert(type(fn) == 'function')
   local status, rv = pcall(fn, ...)
   if status then
     return status, rv
@@ -238,7 +238,7 @@ end
 --    matches('e[or]+$', pcall_err(function(a, b) error('some error') end, 'arg1', 'arg2'))
 --
 function module.pcall_err_withfile(fn, ...)
-  assert(type(fn) == 'function')
+  luaassert(type(fn) == 'function')
   local status, rv = module.pcall(fn, ...)
   if status == true then
     error('expected failure, but got success')
@@ -315,7 +315,7 @@ function module.check_logs()
     for tail in vim.fs.dir(log_dir) do
       if tail:sub(1, 30) == 'valgrind-' or tail:find('san%.') then
         local file = log_dir .. '/' .. tail
-        local fd = io.open(file)
+        local fd = assert(io.open(file))
         local start_msg = ('='):rep(20) .. ' File ' .. file .. ' ' .. ('='):rep(20)
         local lines = {}
         local warning_line = 0
@@ -350,7 +350,7 @@ function module.check_logs()
       end
     end
   end
-  assert(
+  luaassert(
     0 == #runtime_errors,
     string.format('Found runtime errors in logfile(s): %s', table.concat(runtime_errors, ', '))
   )
@@ -757,7 +757,7 @@ function module.format_luav(v, indent, opts)
   else
     print(type(v))
     -- Not implemented yet
-    assert(false)
+    luaassert(false)
   end
   return ret
 end
@@ -805,7 +805,7 @@ end
 
 local fixtbl_metatable = {
   __newindex = function()
-    assert(false)
+    luaassert(false)
   end,
 }
 
@@ -902,7 +902,7 @@ end
 
 -- Dedent the given text and write it to the file name.
 function module.write_file(name, text, no_dedent, append)
-  local file = io.open(name, (append and 'a' or 'w'))
+  local file = assert(io.open(name, (append and 'a' or 'w')))
   if type(text) == 'table' then
     -- Byte blob
     local bytes = text
@@ -920,7 +920,7 @@ end
 
 function module.is_ci(name)
   local any = (name == nil)
-  assert(any or name == 'github' or name == 'cirrus')
+  luaassert(any or name == 'github' or name == 'cirrus')
   local gh = ((any or name == 'github') and nil ~= os.getenv('GITHUB_ACTIONS'))
   local cirrus = ((any or name == 'cirrus') and nil ~= os.getenv('CIRRUS_CI'))
   return gh or cirrus
diff --git a/test/unit/helpers.lua b/test/unit/helpers.lua
index e56f8d5058..86d02e8c31 100644
--- a/test/unit/helpers.lua
+++ b/test/unit/helpers.lua
@@ -19,7 +19,7 @@ for _, p in ipairs(Paths.include_paths) do
   Preprocess.add_to_include_path(p)
 end
 
-local child_pid = nil --- @type integer
+local child_pid = nil --- @type integer?
 --- @generic F: function
 --- @param func F
 --- @return F