Provide better error message for keywords access with non-atom keys

Author: lexmag

lib/elixir/lib/access.ex

@@ -60,6 +60,11 @@ defmodule Access do
     end
   end
 
+  def fetch(list, key) when is_list(list) do
+    raise ArgumentError,
+      "the Access calls for keywords expect the key to be an atom, got: " <> inspect(key)
+  end
+
   def fetch(nil, _key) do
     :error
   end

lib/elixir/test/elixir/access_test.exs

@@ -36,8 +36,9 @@ defmodule AccessTest do
     assert Access.fetch([foo: :bar], :foo) == {:ok, :bar}
     assert Access.fetch([foo: :bar], :bar) == :error
 
-    assert_raise FunctionClauseError, fn ->
-      Access.fetch([{"foo", :bar}], "foo")
+    msg = ~r/the Access calls for keywords expect the key to be an atom/
+    assert_raise ArgumentError, msg,  fn ->
+      Access.fetch([], "foo")
     end
 
     assert Access.get([foo: :bar], :foo) == :bar