Ensure implicit multipart templates with locale works as expected.

actionmailer/lib/action_mailer/base.rb

@@ -1,5 +1,8 @@
 require 'active_support/core_ext/class'
+require 'active_support/core_ext/object/blank'
+require 'active_support/core_ext/array/uniq_by'
 require 'active_support/core_ext/module/delegation'
+require 'active_support/core_ext/string/inflections'
 require 'mail'
 require 'action_mailer/tmail_compat'
 require 'action_mailer/collector'
@@ -455,6 +458,8 @@ module ActionMailer #:nodoc:
     def each_template(&block) #:nodoc:
       self.class.view_paths.each do |load_paths|
         templates = load_paths.find_all(action_name, {}, self.class.mailer_name)
+        templates = templates.uniq_by { |t| t.details[:formats] }
+
         unless templates.empty?
           templates.each(&block)
           return

actionmailer/test/base_test.rb

@@ -34,6 +34,10 @@ class BaseTest < ActiveSupport::TestCase
       mail(DEFAULT_HEADERS.merge(hash))
     end
 
+    def implicit_with_locale(hash = {})
+      mail(DEFAULT_HEADERS.merge(hash))
+    end
+
     def explicit_multipart(hash = {})
       attachments['invoice.pdf'] = 'This is test File content' if hash.delete(:attachments)
       mail(DEFAULT_HEADERS.merge(hash)) do |format|
@@ -310,6 +314,29 @@ class BaseTest < ActiveSupport::TestCase
     assert_equal(1, BaseMailer.deliveries.length)
   end
 
+  test "implicit multipart with default locale" do
+    email = BaseMailer.implicit_with_locale.deliver
+    assert_equal(2, email.parts.size)
+    assert_equal("multipart/alternate", email.mime_type)
+    assert_equal("text/plain", email.parts[0].mime_type)
+    assert_equal("Implicit with locale TEXT", email.parts[0].body.encoded)
+    assert_equal("text/html", email.parts[1].mime_type)
+    assert_equal("Implicit with locale EN HTML", email.parts[1].body.encoded)
+  end
+
+  test "implicit multipart with other locale" do
+    swap I18n, :locale => :pl do
+      email = BaseMailer.implicit_with_locale.deliver
+      assert_equal(2, email.parts.size)
+      assert_equal("multipart/alternate", email.mime_type)
+      assert_equal("text/plain", email.parts[0].mime_type)
+      assert_equal("Implicit with locale PL TEXT", email.parts[0].body.encoded)
+      assert_equal("text/html", email.parts[1].mime_type)
+      assert_equal("Implicit with locale HTML", email.parts[1].body.encoded)
+    end
+  end
+
+
   protected
 
     # Execute the block setting the given values and restoring old values after

actionmailer/test/fixtures/base_mailer/implicit_with_locale.en.html.erb

@@ -0,0 +1 @@
+Implicit with locale EN HTML

actionmailer/test/fixtures/base_mailer/implicit_with_locale.html.erb

@@ -0,0 +1 @@
+Implicit with locale HTML

actionmailer/test/fixtures/base_mailer/implicit_with_locale.pl.text.erb

@@ -0,0 +1 @@
+Implicit with locale PL TEXT

actionmailer/test/fixtures/base_mailer/implicit_with_locale.text.erb

@@ -0,0 +1 @@
+Implicit with locale TEXT