feature(assertions): Add assertions module with type checker

assertions.lua

@@ -0,0 +1,33 @@
+local _,_,module = ...
+module = module or {}
+assert(type(module) == 'table', 'must provide a table to extend')
+-----------
+
+-- NOTE(dabrady) The 'checks' package sets some globals. I don't want that
+-- if I can avoid it, so if it hasn't already been loaded, I'm going to
+-- prevent it by encapsulating them and then unsetting the globals immediately.
+-- But if it has already been loaded, I don't want to mess with them: they
+-- could be being used by others.
+-- @see https://luarocks.org/modules/luarocks/
+do
+  local checks_already_loaded = package.loaded.checks
+  require('checks')
+
+  -- @see https://github.com/SierraWireless/luasched/blob/99e025548d772710439a28d487276cbdb5d4ccd7/c/checks.c#L291-L294
+  module.__checks__ = checks
+  module.__checkers__ = checkers
+
+  if not checks_already_loaded then
+    checks = nil
+    checkers = nil
+  end
+end
+
+-- Provide less magical type assertion.
+function module.assert_type(val, t)
+  module.__checks__(t) -- Asserts against the first argument to `assert_type`
+  return val
+end
+
+-----------
+return module