Merge pull request #35446 from jhawthorn/actionmailer_format_assignment

Add test and change how format set in ActionMailer

actionmailer/lib/action_mailer/base.rb

@@ -974,9 +974,8 @@ module ActionMailer
 
         each_template(Array(templates_path), templates_name).map do |template|
           format = template.format || self.formats.first
-          self.formats = [format]
           {
-            body: render(template: template),
+            body: render(template: template, formats: [format]),
             content_type: Mime[format].to_s
           }
         end

actionmailer/test/base_test.rb

@@ -307,6 +307,16 @@ class BaseTest < ActiveSupport::TestCase
     assert_equal("HTML Implicit Multipart", email.parts[1].body.encoded)
   end
 
+  test "implicit multipart formats" do
+    email = BaseMailer.implicit_multipart_formats
+    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 Multipart [:text]", email.parts[0].body.encoded)
+    assert_equal("text/html", email.parts[1].mime_type)
+    assert_equal("Implicit Multipart [:html]", email.parts[1].body.encoded)
+  end
+
   test "implicit multipart with sort order" do
     order = ["text/html", "text/plain"]
     with_default BaseMailer, parts_order: order do

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

@@ -0,0 +1 @@
+Implicit Multipart <%= formats.inspect %>

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

@@ -0,0 +1 @@
+Implicit Multipart <%= formats.inspect %>

actionmailer/test/mailers/base_mailer.rb

@@ -62,6 +62,10 @@ class BaseMailer < ActionMailer::Base
     mail(hash)
   end
 
+  def implicit_multipart_formats(hash = {})
+    mail(hash)
+  end
+
   def implicit_with_locale(hash = {})
     mail(hash)
   end