DRY up json protocol usage

lib/ecto/json.ex

@@ -1,97 +1,52 @@
-if Code.ensure_loaded?(Jason.Encoder) do
-  defimpl Jason.Encoder, for: Ecto.Association.NotLoaded do
-    def encode(%{__owner__: owner, __field__: field}, _) do
-      raise """
-      cannot encode association #{inspect(field)} from #{inspect(owner)} to \
-      JSON because the association was not loaded.
+for encoder <- [Jason.Encoder, JSON.Encoder] do
+  module = Macro.inspect_atom(:literal, encoder)
 
-      You can either preload the association:
+  if Code.ensure_loaded?(encoder) do
+    defimpl encoder, for: Ecto.Association.NotLoaded do
+      def encode(%{__owner__: owner, __field__: field}, _) do
+        raise """
+        cannot encode association #{inspect(field)} from #{inspect(owner)} to \
+        JSON because the association was not loaded.
 
-          Repo.preload(#{inspect(owner)}, #{inspect(field)})
+        You can either preload the association:
 
-      Or choose to not encode the association when converting the struct \
-      to JSON by explicitly listing the JSON fields in your schema:
+            Repo.preload(#{inspect(owner)}, #{inspect(field)})
 
-          defmodule #{inspect(owner)} do
-            # ...
+        Or choose to not encode the association when converting the struct \
+        to JSON by explicitly listing the JSON fields in your schema:
 
-            @derive {Jason.Encoder, only: [:name, :title, ...]}
-            schema ... do
+            defmodule #{inspect(owner)} do
+              # ...
 
-      You can also use the :except option instead of :only if you would \
-      prefer to skip some fields.
-      """
-    end
-  end
-
-  defimpl Jason.Encoder, for: Ecto.Schema.Metadata do
-    def encode(%{schema: schema}, _) do
-      raise """
-      cannot encode metadata from the :__meta__ field for #{inspect(schema)} \
-      to JSON. This metadata is used internally by Ecto and should never be \
-      exposed externally.
-
-      You can either map the schemas to remove the :__meta__ field before \
-      encoding or explicitly list the JSON fields in your schema:
-
-          defmodule #{inspect(schema)} do
-            # ...
+              @derive {#{unquote(module)}, only: [:name, :title, ...]}
+              schema ... do
 
-            @derive {Jason.Encoder, only: [:name, :title, ...]}
-            schema ... do
-
-      You can also use the :except option instead of :only if you would \
-      prefer to skip some fields.
-      """
+        You can also use the :except option instead of :only if you would \
+        prefer to skip some fields.
+        """
+      end
     end
-  end
-end
-
-if Code.ensure_loaded?(JSON.Encoder) do
-  defimpl JSON.Encoder, for: Ecto.Association.NotLoaded do
-    def encode(%{__owner__: owner, __field__: field}, _) do
-      raise """
-      cannot encode association #{inspect(field)} from #{inspect(owner)} to \
-      JSON because the association was not loaded.
-
-      You can either preload the association:
-
-          Repo.preload(#{inspect(owner)}, #{inspect(field)})
-
-      Or choose to not encode the association when converting the struct \
-      to JSON by explicitly listing the JSON fields in your schema:
-
-          defmodule #{inspect(owner)} do
-            # ...
-
-            @derive {JSON.Encoder, only: [:name, :title, ...]}
-            schema ... do
-
-      You can also use the :except option instead of :only if you would \
-      prefer to skip some fields.
-      """
-    end
-  end
 
-  defimpl JSON.Encoder, for: Ecto.Schema.Metadata do
-    def encode(%{schema: schema}, _) do
-      raise """
-      cannot encode metadata from the :__meta__ field for #{inspect(schema)} \
-      to JSON. This metadata is used internally by Ecto and should never be \
-      exposed externally.
+    defimpl encoder, for: Ecto.Schema.Metadata do
+      def encode(%{schema: schema}, _) do
+        raise """
+        cannot encode metadata from the :__meta__ field for #{inspect(schema)} \
+        to JSON. This metadata is used internally by Ecto and should never be \
+        exposed externally.
 
-      You can either map the schemas to remove the :__meta__ field before \
-      encoding or explicitly list the JSON fields in your schema:
+        You can either map the schemas to remove the :__meta__ field before \
+        encoding or explicitly list the JSON fields in your schema:
 
-          defmodule #{inspect(schema)} do
-            # ...
+            defmodule #{inspect(schema)} do
+              # ...
 
-            @derive {JSON.Encoder, only: [:name, :title, ...]}
-            schema ... do
+              @derive {#{unquote(module)}, only: [:name, :title, ...]}
+              schema ... do
 
-      You can also use the :except option instead of :only if you would \
-      prefer to skip some fields.
-      """
+        You can also use the :except option instead of :only if you would \
+        prefer to skip some fields.
+        """
+      end
     end
   end
 end

test/ecto/json_test.exs

@@ -3,7 +3,10 @@ defmodule Ecto.JsonTest do
 
   @implementations [{Jason, Jason.Encoder}, {JSON, JSON.Encoder}]
 
-  loaded_implementations = for {_lib, encoder} = implementation <- @implementations, Code.ensure_loaded?(encoder), do: implementation
+  loaded_implementations =
+    for {_lib, encoder} = implementation <- @implementations,
+        Code.ensure_loaded?(encoder),
+        do: implementation
 
   defmodule User do
     use Ecto.Schema
@@ -15,7 +18,6 @@ defmodule Ecto.JsonTest do
   end
 
   for {json_library, _encoder} <- loaded_implementations do
-
     describe to_string(json_library) do
       test "encodes decimal" do
         decimal = Decimal.new("1.0")
@@ -24,14 +26,14 @@ defmodule Ecto.JsonTest do
 
       test "fails on association not loaded" do
         assert_raise RuntimeError,
-                    ~r/cannot encode association :comments from Ecto.JsonTest.User to JSON/,
-                    fn -> unquote(json_library).encode!(%User{}.comments) end
+                     ~r/cannot encode association :comments from Ecto.JsonTest.User to JSON/,
+                     fn -> unquote(json_library).encode!(%User{}.comments) end
       end
 
       test "fails when encoding __meta__" do
         assert_raise RuntimeError,
-                    ~r/cannot encode metadata from the :__meta__ field for Ecto.JsonTest.User to JSON/,
-                    fn -> unquote(json_library).encode!(%User{comments: []}) end
+                     ~r/cannot encode metadata from the :__meta__ field for Ecto.JsonTest.User to JSON/,
+                     fn -> unquote(json_library).encode!(%User{comments: []}) end
       end
     end
   end