fix(cache): explain how to fix a missing Nebulex.Adapter.CompositeKV

Author: cabol

lib/nebulex/cache/options.ex

@@ -461,7 +461,7 @@ defmodule Nebulex.Cache.Options do
       behaviour ->
         msg =
           "#{target} expects the option value #{inspect(value)} " <>
-            "to list #{inspect(behaviour)} as a behaviour"
+            "to list #{inspect(behaviour)} as a behaviour" <> behaviour_hint(behaviour)
 
         {:error, msg}
     end
@@ -472,6 +472,17 @@ defmodule Nebulex.Cache.Options do
     {:error, "expected a module, got: #{inspect(value)}"}
   end
 
+  # Nebulex v3.1 made Nebulex.Adapter.CompositeKV mandatory, so an adapter
+  # built for v3.0 fails here; tell the user how to fix it
+  defp behaviour_hint(Nebulex.Adapter.CompositeKV) do
+    ". Add `use Nebulex.Adapter.CompositeKV` to the adapter, " <>
+      "or upgrade it to a version built for Nebulex v3.1 or later"
+  end
+
+  defp behaviour_hint(_behaviour) do
+    ""
+  end
+
   ## Extras
 
   @doc """

test/nebulex/cache/supervisor_test.exs

@@ -86,7 +86,9 @@ defmodule Nebulex.Cache.SupervisorTest do
       msg =
         "invalid value for :adapter option: Nebulex.Cache expects the option value " <>
           "Nebulex.Cache.SupervisorTest.NoCompositeKVAdapter to list " <>
-          "Nebulex.Adapter.CompositeKV as a behaviour"
+          "Nebulex.Adapter.CompositeKV as a behaviour. Add " <>
+          "`use Nebulex.Adapter.CompositeKV` to the adapter, or upgrade it to " <>
+          "a version built for Nebulex v3.1 or later"
 
       assert_raise NimbleOptions.ValidationError, msg, fn ->
         defmodule NoCompositeKVAdapter do