Template lookup now respect default locale and I18n fallbacks.

Given the following templates:

    mailer/demo.html.erb
    mailer/demo.en.html.erb
    mailer/demo.pt.html.erb

Before this change for a locale that doesn't have its related file
the `mailer/demo.html.erb` will
be rendered even if `en` is the default locale.

Now `mailer/demo.en.html.erb` has precedence over the file without
 locale.

Also, it is possible to give a fallback.

    mailer/demo.pt.html.erb
    mailer/demo.pt-BR.html.erb

So if the locale is `pt-PT`, `mailer/demo.pt.html.erb` will be
 rendered given the right I18n fallback configuration.

Fixes #11884.

3 files changed, 28 insertions, 1 deletions

diff --git a/actionmailer/test/base_test.rb b/actionmailer/test/base_test.rb
index 396d0a95b5..5d9eda2555 100644
--- a/actionmailer/test/base_test.rb
+++ b/actionmailer/test/base_test.rb
@@ -353,10 +353,35 @@ class BaseTest < ActiveSupport::TestCase
       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)
+      assert_equal("Implicit with locale EN HTML", email.parts[1].body.encoded)
     end
   end
 
+  test "implicit multipart with fallback locale" do
+    fallback_backend = Class.new(I18n::Backend::Simple) do
+      include I18n::Backend::Fallbacks
+    end
+
+    begin
+      backend = I18n.backend
+      I18n.backend = fallback_backend.new
+      I18n.fallbacks[:"de-AT"] = [:de]
+
+      swap I18n, locale: 'de-AT' do
+        email = BaseMailer.implicit_with_locale
+        assert_equal(2, email.parts.size)
+        assert_equal("multipart/alternative", email.mime_type)
+        assert_equal("text/plain", email.parts[0].mime_type)
+        assert_equal("Implicit with locale DE-AT TEXT", email.parts[0].body.encoded)
+        assert_equal("text/html", email.parts[1].mime_type)
+        assert_equal("Implicit with locale DE HTML", email.parts[1].body.encoded)
+      end
+    ensure
+      I18n.backend = backend
+    end
+  end
+
+
   test "implicit multipart with several view paths uses the first one with template" do
     old = BaseMailer.view_paths
     begin
diff --git a/actionmailer/test/fixtures/base_mailer/implicit_with_locale.de-AT.text.erb b/actionmailer/test/fixtures/base_mailer/implicit_with_locale.de-AT.text.erb
new file mode 100644
index 0000000000..e97505fad9
--- /dev/null
+++ b/actionmailer/test/fixtures/base_mailer/implicit_with_locale.de-AT.text.erb
@@ -0,0 +1 @@
+Implicit with locale DE-AT TEXT
\ No newline at end of file
diff --git a/actionmailer/test/fixtures/base_mailer/implicit_with_locale.de.html.erb b/actionmailer/test/fixtures/base_mailer/implicit_with_locale.de.html.erb
new file mode 100644
index 0000000000..0536b5d3e2
--- /dev/null
+++ b/actionmailer/test/fixtures/base_mailer/implicit_with_locale.de.html.erb
@@ -0,0 +1 @@
+Implicit with locale DE HTML
\ No newline at end of file