Raise ArgumentError when inspect protocol options don't match struct (#11801)

Author: jwharrow

lib/elixir/lib/inspect.ex

@@ -455,6 +455,9 @@ defimpl Inspect, for: Any do
     only = Keyword.get(options, :only, fields)
     except = Keyword.get(options, :except, [])
 
+    :ok = validate_option(only, fields, module)
+    :ok = validate_option(except, fields, module)
+
     filtered_fields =
       fields
       |> Enum.reject(&(&1 in except))
@@ -478,6 +481,17 @@ defimpl Inspect, for: Any do
     end
   end
 
+  defp validate_option(option_list, fields, module) do
+    case option_list -- fields do
+      [] ->
+        :ok
+
+      unknown_fields ->
+        raise ArgumentError,
+              "unknown fields #{Kernel.inspect(unknown_fields)} given when deriving the Inspect protocol for #{Kernel.inspect(module)}. :only and :except values must match struct fields"
+    end
+  end
+
   def inspect(%module{} = struct, opts) do
     try do
       module.__struct__()

lib/elixir/test/elixir/inspect_test.exs

@@ -694,6 +694,28 @@ defmodule Inspect.MapTest do
              "%Inspect.MapTest.StructWithAllFieldsInOnlyOption{\n  a: 1,\n  b: 2\n}"
   end
 
+  test "struct missing fields in the :only option" do
+    assert_raise ArgumentError,
+                 "unknown fields [:c] given when deriving the Inspect protocol for Inspect.MapTest.StructMissingFieldsInOnlyOption. :only and :except values must match struct fields",
+                 fn ->
+                   defmodule StructMissingFieldsInOnlyOption do
+                     @derive {Inspect, only: [:c]}
+                     defstruct [:a, :b]
+                   end
+                 end
+  end
+
+  test "struct missing fields in the :except option" do
+    assert_raise ArgumentError,
+                 "unknown fields [:c, :d] given when deriving the Inspect protocol for Inspect.MapTest.StructMissingFieldsInExceptOption. :only and :except values must match struct fields",
+                 fn ->
+                   defmodule StructMissingFieldsInExceptOption do
+                     @derive {Inspect, except: [:c, :d]}
+                     defstruct [:a, :b]
+                   end
+                 end
+  end
+
   defmodule StructWithExceptOption do
     @derive {Inspect, except: [:b, :c]}
     defstruct [:a, :b, :c, :d]