raise compile error when inspect protocol options don't match struct

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, __CALLER__)
+    :ok = validate_option(except, fields, module, __CALLER__)
+
     filtered_fields =
       fields
       |> Enum.reject(&(&1 in except))
@@ -478,6 +481,15 @@ defimpl Inspect, for: Any do
     end
   end
 
+  defp validate_option(option_list, fields, module, caller) do
+    if not Enum.empty?(option_list -- fields) do
+      description = "When deriving inspect protocol of #{module}, values must match struct fields"
+      raise CompileError, file: caller.file, line: caller.line, description: description
+    end
+
+    :ok
+  end
+
   def inspect(%module{} = struct, opts) do
     try do
       module.__struct__()

lib/elixir/test/elixir/inspect_test.exs

@@ -694,6 +694,30 @@ defmodule Inspect.MapTest do
              "%Inspect.MapTest.StructWithAllFieldsInOnlyOption{\n  a: 1,\n  b: 2\n}"
   end
 
+  test "struct missing fields in the :only option" do
+    message =
+      ~r"When deriving inspect protocol of Elixir.Inspect.MapTest.StructMissingFieldsInOnlyOption, values must match struct fields"
+
+    assert_raise CompileError, message, fn ->
+      defmodule StructMissingFieldsInOnlyOption do
+        @derive {Inspect, only: [:c]}
+        defstruct [:a, :b]
+      end
+    end
+  end
+
+  test "struct missing fields in the :except option" do
+    message =
+      ~r"When deriving inspect protocol of Elixir.Inspect.MapTest.StructMissingFieldsInExceptOption, values must match struct fields"
+
+    assert_raise CompileError, message, fn ->
+      defmodule StructMissingFieldsInExceptOption do
+        @derive {Inspect, except: [:c]}
+        defstruct [:a, :b]
+      end
+    end
+  end
+
   defmodule StructWithExceptOption do
     @derive {Inspect, except: [:b, :c]}
     defstruct [:a, :b, :c, :d]