Allow optional: :all when deriving Inspect

Author: sabiwara

lib/elixir/lib/inspect.ex

@@ -67,7 +67,8 @@ defprotocol Inspect do
     * `:optional` - (since v1.14.0) a list of fields that should not be
       included when they match their default value. This can be used to
       simplify the struct representation at the cost of hiding
-      information.
+      information. Since v1.19.0, the `:all` atom can be passed to
+      mark all fields as optional.
 
   Whenever `:only` or `:except` are used to restrict fields,
   the struct will be printed using the `#User<...>` notation,
@@ -159,11 +160,19 @@ defprotocol Inspect do
 
     only = Keyword.get(options, :only, fields)
     except = Keyword.get(options, :except, [])
-    optional = Keyword.get(options, :optional, [])
 
     :ok = validate_option(:only, only, fields, module)
     :ok = validate_option(:except, except, fields, module)
-    :ok = validate_option(:optional, optional, fields, module)
+
+    optional =
+      case Keyword.get(options, :optional, []) do
+        :all ->
+          fields
+
+        optional ->
+          :ok = validate_option(:optional, optional, fields, module)
+          optional
+      end
 
     inspect_module =
       if fields == Enum.sort(only) and except == [] do

lib/elixir/test/elixir/inspect_test.exs

@@ -772,6 +772,20 @@ defmodule Inspect.MapTest do
     assert inspect(struct) ==
              "#Inspect.MapTest.StructWithExceptOptionalAndOrder<d: nil, a: nil, ...>"
   end
+
+  defmodule StructWithOptionalAll do
+    @derive {Inspect, optional: :all}
+    defstruct [:a, :b, :c, :d]
+  end
+
+  test "struct with :optional set to :all" do
+    struct = %StructWithOptionalAll{a: 1, b: 2}
+
+    assert inspect(struct) == "%Inspect.MapTest.StructWithOptionalAll{a: 1, b: 2}"
+
+    struct = %StructWithOptionalAll{}
+    assert inspect(struct) == "%Inspect.MapTest.StructWithOptionalAll{}"
+  end
 end
 
 defmodule Inspect.OthersTest do