Fix the t/1 IEx helper for private types (elixir-lang#8218)

Closes elixir-lang#8208.

lib/iex/lib/iex/introspection.ex

@@ -636,13 +636,14 @@ defmodule IEx.Introspection do
 
       {:ok, types} ->
         printed =
-          for {_, {^type, _, args}} = typespec <- types do
+          for {kind, {^type, _, args}} = typespec <- types,
+              kind != :typep do
             type_doc(module, type, length(args), typespec)
             |> print_typespec()
           end
 
         if printed == [] do
-          types_not_found("#{inspect(module)}.#{type}")
+          types_not_found_or_private("#{inspect(module)}.#{type}")
         end
     end
 
@@ -656,13 +657,15 @@ defmodule IEx.Introspection do
 
       {:ok, types} ->
         printed =
-          for {_, {^type, _, args}} = typespec <- types, length(args) == arity do
+          for {kind, {^type, _, args}} = typespec <- types,
+              kind != :typep,
+              length(args) == arity do
             type_doc(module, type, arity, typespec)
             |> print_typespec()
           end
 
         if printed == [] do
-          types_not_found("#{inspect(module)}.#{type}")
+          types_not_found_or_private("#{inspect(module)}.#{type}")
         end
     end
 
@@ -769,6 +772,10 @@ defmodule IEx.Introspection do
   defp types_not_found(for), do: not_found(for, "type information")
   defp docs_not_found(for), do: not_found(for, "documentation")
 
+  defp types_not_found_or_private(for) do
+    puts_error("No type information for #{for} was found or #{for} is private")
+  end
+
   defp behaviour_found(for) do
     puts_error("""
     No documentation for function #{for} was found, but there is a callback with the same name.

lib/iex/test/iex/helpers_test.exs

@@ -671,8 +671,30 @@ defmodule IEx.HelpersTest do
   end
 
   describe "t" do
-    test "prints when there is no type information" do
+    test "prints when there is no type information or the type is private" do
       assert capture_io(fn -> t(IEx) end) == "No type information for IEx was found\n"
+
+      assert capture_io(fn -> t(Enum.doesnt_exist()) end) ==
+               "No type information for Enum.doesnt_exist was found or " <>
+                 "Enum.doesnt_exist is private\n"
+
+      contents = """
+      defmodule TypeSample do
+        @type public_so_t_doesnt_warn() :: t()
+        @typep t() :: term()
+      end
+      """
+
+      filename = "typesample.ex"
+
+      with_file(filename, contents, fn ->
+        assert c(filename, ".") == [TypeSample]
+
+        assert capture_io(fn -> t(TypeSample.t() / 0) end) ==
+                 "No type information for TypeSample.t was found or TypeSample.t is private\n"
+      end)
+    after
+      cleanup_modules([TypeSample])
     end
 
     test "prints all types in module" do