Raise if adapter does not support attachments yet

Not all adapters will support attachments right away. This makes it so
that if you try to add an attachment, but are using an adapter that
doesn't do anything with them, it raises letting you know that's the
problem. Otherwise it would be successful, but the attachments would do
nothing

lib/bamboo/adapters/mandrill_adapter.ex

@@ -52,6 +52,9 @@ defmodule Bamboo.MandrillAdapter do
     end
   end
 
+  @doc false
+  def supports_attachments?, do: true
+
   defp get_key(config) do
     case Map.get(config, :api_key) do
       nil -> raise_api_key_error(config)

lib/bamboo/mailer.ex

@@ -114,7 +114,7 @@ defmodule Bamboo.Mailer do
 
   @doc false
   def deliver_now(adapter, email, config) do
-    email = email |> validate_and_normalize
+    email = email |> validate_and_normalize(adapter)
 
     if email.to == [] && email.cc == [] && email.bcc == [] do
       debug_unsent(email)
@@ -127,7 +127,7 @@ defmodule Bamboo.Mailer do
 
   @doc false
   def deliver_later(adapter, email, config) do
-    email = email |> validate_and_normalize
+    email = email |> validate_and_normalize(adapter)
 
     if email.to == [] && email.cc == [] && email.bcc == [] do
       debug_unsent(email)
@@ -154,14 +154,24 @@ defmodule Bamboo.Mailer do
     """
   end
 
-  defp validate_and_normalize(email) do
-    email |> validate |> normalize_addresses
+  defp validate_and_normalize(email, adapter) do
+    email |> validate(adapter) |> normalize_addresses
   end
 
-  defp validate(email) do
+  defp validate(email, adapter) do
     email
     |> validate_from_address
     |> validate_recipients
+    |> validate_attachment_support(adapter)
+  end
+
+  defp validate_attachment_support(%{attachments: []} = email, _adapter), do: email
+  defp validate_attachment_support(email, adapter) do
+    if function_exported?(adapter, :supports_attachments?, 0) && adapter.supports_attachments? do
+      email
+    else
+      raise "the #{adapter} does not support attachments yet."
+    end
   end
 
   defp validate_from_address(%{from: nil}) do

test/lib/bamboo/adapters/mandrill_adapter_test.exs

@@ -105,6 +105,7 @@ defmodule Bamboo.MandrillAdapterTest do
 
     email |> MandrillAdapter.deliver(@config)
 
+    assert MandrillAdapter.supports_attachments?
     assert_receive {:fake_mandrill, %{params: params}}
     assert params["key"] == @config[:api_key]
     message = params["message"]

test/lib/bamboo/mailer_test.exs

@@ -8,6 +8,8 @@ defmodule Bamboo.MailerTest do
     end
 
     def handle_config(config), do: config
+
+    def supports_attachments?, do: true
   end
 
   defmodule CustomConfigAdapter do
@@ -20,6 +22,14 @@ defmodule Bamboo.MailerTest do
     end
   end
 
+  defmodule AdapterWithoutAttachmentSupport do
+    def deliver(_email, _config) do
+      :noop
+    end
+
+    def handle_config(config), do: config
+  end
+
   @custom_config adapter: CustomConfigAdapter, foo: :bar
 
   Application.put_env(:bamboo, __MODULE__.CustomConfigMailer, @custom_config)
@@ -28,6 +38,14 @@ defmodule Bamboo.MailerTest do
     use Bamboo.Mailer, otp_app: :bamboo
   end
 
+  @mailer_config adapter: AdapterWithoutAttachmentSupport, foo: :bar
+
+  Application.put_env(:bamboo, __MODULE__.AdapterWithoutAttachmentSupportMailer, @mailer_config)
+
+  defmodule AdapterWithoutAttachmentSupportMailer do
+    use Bamboo.Mailer, otp_app: :bamboo
+  end
+
   @mailer_config adapter: FooAdapter, foo: :bar
 
   Application.put_env(:bamboo, __MODULE__.FooMailer, @mailer_config)
@@ -41,6 +59,33 @@ defmodule Bamboo.MailerTest do
     :ok
   end
 
+  test "raise if adapter does not support attachments and attachments are sent" do
+    path = Path.join(__DIR__, "../../support/attachment.docx")
+    email = new_email(to: "foo@bar.com") |> Email.put_attachment(path)
+
+    assert_raise RuntimeError, ~r/does not support attachments/, fn ->
+      AdapterWithoutAttachmentSupportMailer.deliver_now(email)
+    end
+
+    assert_raise RuntimeError, ~r/does not support attachments/, fn ->
+      AdapterWithoutAttachmentSupportMailer.deliver_later(email)
+    end
+  end
+
+  test "does not raise if adapter supports attachments" do
+    path = Path.join(__DIR__, "../../support/attachment.docx")
+    email = new_email(to: "foo@bar.com") |> Email.put_attachment(path)
+
+    FooMailer.deliver_now(email)
+
+    assert_received {:deliver, _email, _config}
+  end
+
+  test "does not raise if no attachments are on the email" do
+    email = new_email(to: "foo@bar.com")
+    AdapterWithoutAttachmentSupportMailer.deliver_now(email)
+  end
+
   test "uses adapter's handle_config/1 to customize or validate the config" do
     email = new_email(to: "foo@bar.com")