Fix is_record tests to check tuple_size before accessing the first element

Author: Devin Torres

lib/elixir/lib/kernel.ex

@@ -1558,12 +1558,14 @@ defmodule Kernel do
     case __CALLER__.in_guard? do
       true ->
         quote do
-          is_tuple(unquote(thing)) and :erlang.element(1, unquote(thing)) == unquote(kind)
+          is_tuple(unquote(thing)) and tuple_size(unquote(thing)) > 0
+            and :erlang.element(1, unquote(thing)) == unquote(kind)
         end
       false ->
         quote do
           result = unquote(thing)
-          is_tuple(result) and :erlang.element(1, result) == unquote(kind)
+          is_tuple(result) and tuple_size(unquote(thing)) > 0
+            and :erlang.element(1, result) == unquote(kind)
         end
     end
   end
@@ -1575,12 +1577,14 @@ defmodule Kernel do
     case __CALLER__.in_guard? do
       true ->
         quote do
-          is_tuple(unquote(thing)) and is_atom(:erlang.element(1, unquote(thing)))
+          is_tuple(unquote(thing)) and tuple_size(unquote(thing)) > 0
+            and is_atom(:erlang.element(1, unquote(thing)))
         end
       false ->
         quote do
           result = unquote(thing)
-          is_tuple(result) and is_atom(:erlang.element(1, result))
+          is_tuple(result) and tuple_size(unquote(thing)) > 0
+            and is_atom(:erlang.element(1, result))
         end
     end
   end

lib/elixir/test/elixir/exception_test.exs

@@ -5,7 +5,9 @@ defmodule Kernel.ExceptionTest do
 
   test :is_exception do
     assert is_exception(RuntimeError.new)
-    refute is_exception({ :foo, :bar })
+    refute is_exception(empty_tuple)
+    refute is_exception(a_tuple)
+    refute is_exception(a_list)
   end
 
   test :format_entry_with_no_file_or_line do
@@ -74,4 +76,8 @@ defmodule Kernel.ExceptionTest do
   test :erlang_error_message do
     assert ErlangError.new(original: :sample).message == "erlang error: :sample"
   end
-end
+
+  defp empty_tuple, do: {}
+  defp a_tuple, do: { :foo, :bar, :baz }
+  defp a_list,  do: [ :foo, :bar, :baz ]
+end

lib/elixir/test/elixir/record_test.exs

@@ -103,6 +103,11 @@ defmodule RecordTest do
 
   test :is_record do
     assert is_record(RecordTest.FileInfo.new, RecordTest.FileInfo)
+    assert is_record(RecordTest.WithNoField.new)
+    refute is_record(empty_tuple)
+    refute is_record(a_list)
+    refute is_record(empty_tuple, RecordTest.FileInfo)
+    refute is_record(a_tuple, RecordTest.FileInfo)
     refute is_record(a_list, RecordTest.FileInfo)
     refute is_record(RecordTest.FileInfo.new, List)
   end
@@ -177,7 +182,7 @@ defmodule RecordTest do
     file_info
   end
 
-  defp a_list do
-    [:a, :b, :c]
-  end
+  defp empty_tuple, do: {}
+  defp a_tuple, do: { :foo, :bar, :baz }
+  defp a_list,  do: [ :foo, :bar, :baz ]
 end