Allow user to define a type named union (#10055)

Author: cleidiano

lib/elixir/lib/code/typespec.ex

@@ -217,7 +217,8 @@ defmodule Code.Typespec do
   end
 
   defp typespec_to_quoted({:user_type, line, name, args}) do
-    typespec_to_quoted({:type, line, name, args})
+    args = for arg <- args, do: typespec_to_quoted(arg)
+    {name, [line: line], args}
   end
 
   defp typespec_to_quoted({:type, line, :tuple, :any}) do

lib/elixir/test/elixir/typespec_test.exs

@@ -1183,6 +1183,12 @@ defmodule TypespecTest do
       quoted =
         Enum.sort([
           quote(do: @spec(foo() :: integer())),
+          quote(do: @spec(foo() :: union())),
+          quote(do: @spec(foo() :: union(integer()))),
+          quote(do: @spec(foo() :: truly_union())),
+          quote(do: @spec(foo(union()) :: union())),
+          quote(do: @spec(foo(union(integer())) :: union(integer()))),
+          quote(do: @spec(foo(truly_union()) :: truly_union())),
           quote(do: @spec(foo(atom()) :: integer() | [{}])),
           quote(do: @spec(foo(arg) :: integer() when [arg: integer()])),
           quote(do: @spec(foo(arg) :: arg when [arg: var])),
@@ -1191,6 +1197,10 @@ defmodule TypespecTest do
 
       bytecode =
         test_module do
+          @type union :: any()
+          @type union(t) :: t
+          @type truly_union :: list | map | union
+
           def foo(), do: 1
           def foo(arg), do: arg
           Module.eval_quoted(__MODULE__, quote(do: (unquote_splicing(quoted))))