Preserve empty list in dynamic list type constructor

Closes #15488.

Author: josevalim

lib/elixir/lib/module/types/descr.ex

@@ -2133,6 +2133,9 @@ defmodule Module.Types.Descr do
       not dynamic? ->
         dynamic_descr
 
+      static_empty? and empty? ->
+        %{bitmap: @bit_empty_list, dynamic: dynamic_descr}
+
       static_empty? ->
         %{dynamic: dynamic_descr}
 

lib/elixir/test/elixir/module/types/descr_test.exs

@@ -941,6 +941,7 @@ defmodule Module.Types.DescrTest do
             {closed_map([{domain_key(:integer), gradual}]),
              closed_map([{domain_key(:integer), static}]),
              closed_map([{domain_key(:integer), upper_bound}])},
+            {list(dynamic()), empty_list(), list(term())},
             {non_empty_list(gradual), non_empty_list(static), non_empty_list(upper_bound)},
             {non_empty_list(head, gradual), non_empty_list(head, static),
              non_empty_list(head, upper_bound)}