Add clarifications to Access error message

2 files changed, 8 insertions, 4 deletions

diff --git a/lib/elixir/lib/access.ex b/lib/elixir/lib/access.ex
index a9e241ef8..4bc8e067d 100644
--- a/lib/elixir/lib/access.ex
+++ b/lib/elixir/lib/access.ex
@@ -174,7 +174,11 @@ defmodule Access do
       exception =
         case __STACKTRACE__ do
           [unquote(top) | _] ->
-            reason = "#{inspect(unquote(module))} does not implement the Access behaviour"
+            reason =
+              "#{inspect(unquote(module))} does not implement the Access behaviour. " <>
+                "If you are using get_in/put_in/update_in, you can specify the field " <>
+                "to be accessed using Access.key!/1"
+
             %{unquote(exception) | reason: reason}
 
           _ ->
diff --git a/lib/elixir/test/elixir/access_test.exs b/lib/elixir/test/elixir/access_test.exs
index 31cf0f43a..04b7ade83 100644
--- a/lib/elixir/test/elixir/access_test.exs
+++ b/lib/elixir/test/elixir/access_test.exs
@@ -78,21 +78,21 @@ defmodule AccessTest do
     end
 
     message =
-      "function AccessTest.Sample.fetch/2 is undefined (AccessTest.Sample does not implement the Access behaviour)"
+      ~r"function AccessTest.Sample.fetch/2 is undefined \(AccessTest.Sample does not implement the Access behaviour"
 
     assert_raise UndefinedFunctionError, message, fn ->
       Access.fetch(struct(Sample, []), :name)
     end
 
     message =
-      "function AccessTest.Sample.get_and_update/3 is undefined (AccessTest.Sample does not implement the Access behaviour)"
+      ~r"function AccessTest.Sample.get_and_update/3 is undefined \(AccessTest.Sample does not implement the Access behaviour"
 
     assert_raise UndefinedFunctionError, message, fn ->
       Access.get_and_update(struct(Sample, []), :name, fn nil -> {:ok, :baz} end)
     end
 
     message =
-      "function AccessTest.Sample.pop/2 is undefined (AccessTest.Sample does not implement the Access behaviour)"
+      ~r"function AccessTest.Sample.pop/2 is undefined \(AccessTest.Sample does not implement the Access behaviour"
 
     assert_raise UndefinedFunctionError, message, fn ->
       Access.pop(struct(Sample, []), :name)