module T

sig {params(arg: T.nilable(A)).returns(A)}

to contain a non-nil value at this point.
Intended to be used to promise sorbet that a given nilable value happens

needs_foo(foo)
raise "nil" if foo.nil?
foo = maybe_gives_foo

Equivalent to:

needs_foo(T.must(maybe_gives_foo))

Intended to be used as:

otherwise.
A convenience method to `raise` when the argument is `nil` and return it

def self.must(arg)
  return arg if arg
  return arg if arg == false
  begin
    raise TypeError.new("Passed `nil` into T.must")
  rescue TypeError => e # raise into rescue to ensure e.backtrace is populated
    T::Configuration.inline_type_error_handler(e)
  end
end