Pass request params to ActionMailer::Preview

actionmailer/lib/action_mailer/preview.rb

@@ -52,6 +52,12 @@ def register_preview_interceptor(interceptor)
   class Preview
     extend ActiveSupport::DescendantsTracker
 
+    attr_reader :params
+
+    def initialize(params = {})
+      @params = params
+    end
+
     class << self
       # Returns all mailer preview classes.
       def all
@@ -62,8 +68,8 @@ def all
       # Returns the mail object for the given email name. The registered preview
       # interceptors will be informed so that they can transform the message
       # as they would if the mail was actually being delivered.
-      def call(email)
-        preview = new
+      def call(email, params = {})
+        preview = self.new(params)
         message = preview.public_send(email)
         inform_preview_interceptors(message)
         message

actionmailer/test/base_test.rb

@@ -968,3 +968,19 @@ def self.previewing_email(mail); end
     end
   end
 end
+
+class BasePreviewTest < ActiveSupport::TestCase
+  class BaseMailerPreview < ActionMailer::Preview
+    def welcome
+      BaseMailer.welcome(params)
+    end
+  end
+
+  test "has access to params" do
+    params = { name: "World" }
+
+    assert_called_with(BaseMailer, :welcome, [params]) do
+      BaseMailerPreview.call(:welcome, params)
+    end
+  end
+end

railties/lib/rails/mailers_controller.rb

@@ -6,6 +6,8 @@ class Rails::MailersController < Rails::ApplicationController # :nodoc:
   before_action :require_local!, unless: :show_previews?
   before_action :find_preview, only: :preview
 
+  helper_method :part_query
+
   def index
     @previews = ActionMailer::Preview.all
     @page_title = "Mailer Previews"
@@ -19,7 +21,7 @@ def preview
       @email_action = File.basename(params[:path])
 
       if @preview.email_exists?(@email_action)
-        @email = @preview.call(@email_action)
+        @email = @preview.call(@email_action, params)
 
         if params[:part]
           part_type = Mime::Type.lookup(params[:part])
@@ -76,4 +78,8 @@ def find_part(format) # :doc:
         @email
       end
     end
+
+    def part_query(mime_type)
+      request.query_parameters.merge(part: mime_type).to_query
+    end
 end

railties/lib/rails/templates/rails/mailers/email.html.erb

@@ -98,16 +98,16 @@
     <% if @email.multipart? %>
       <dd>
         <select onchange="formatChanged(this);">
-          <option <%= request.format == Mime[:html] ? 'selected' : '' %> value="?part=text%2Fhtml">View as HTML email</option>
-          <option <%= request.format == Mime[:text] ? 'selected' : '' %> value="?part=text%2Fplain">View as plain-text email</option>
+          <option <%= request.format == Mime[:html] ? 'selected' : '' %> value="?<%= part_query('text/html') %>">View as HTML email</option>
+          <option <%= request.format == Mime[:text] ? 'selected' : '' %> value="?<%= part_query('text/plain') %>">View as plain-text email</option>
         </select>
       </dd>
     <% end %>
   </dl>
 </header>
 
 <% if @part && @part.mime_type %>
-  <iframe seamless name="messageBody" src="?part=<%= Rack::Utils.escape(@part.mime_type) %>"></iframe>
+  <iframe seamless name="messageBody" src="?<%= part_query(@part.mime_type) %>"></iframe>
 <% else %>
   <p>
     You are trying to preview an email that does not have any content.

railties/test/application/mailer_previews_test.rb

@@ -485,6 +485,57 @@ def foo
       assert_match '<li><a href="/my_app/rails/mailers/notifier/foo">foo</a></li>', last_response.body
     end
 
+    test "mailer preview receives query params" do
+      mailer "notifier", <<-RUBY
+        class Notifier < ActionMailer::Base
+          default from: "from@example.com"
+
+          def foo(name)
+            @name = name
+            mail to: "to@example.org"
+          end
+        end
+      RUBY
+
+      html_template "notifier/foo", <<-RUBY
+        <p>Hello, <%= @name %>!</p>
+      RUBY
+
+      text_template "notifier/foo", <<-RUBY
+        Hello, <%= @name %>!
+      RUBY
+
+      mailer_preview "notifier", <<-RUBY
+        class NotifierPreview < ActionMailer::Preview
+          def foo
+            Notifier.foo(params[:name] || "World")
+          end
+        end
+      RUBY
+
+      app("development")
+
+      get "/rails/mailers/notifier/foo.txt"
+      assert_equal 200, last_response.status
+      assert_match '<iframe seamless name="messageBody" src="?part=text%2Fplain">', last_response.body
+      assert_match '<option selected value="?part=text%2Fplain">', last_response.body
+      assert_match '<option  value="?part=text%2Fhtml">', last_response.body
+
+      get "/rails/mailers/notifier/foo?part=text%2Fplain"
+      assert_equal 200, last_response.status
+      assert_match %r[Hello, World!], last_response.body
+
+      get "/rails/mailers/notifier/foo.html?name=Ruby"
+      assert_equal 200, last_response.status
+      assert_match '<iframe seamless name="messageBody" src="?name=Ruby&amp;part=text%2Fhtml">', last_response.body
+      assert_match '<option selected value="?name=Ruby&amp;part=text%2Fhtml">', last_response.body
+      assert_match '<option  value="?name=Ruby&amp;part=text%2Fplain">', last_response.body
+
+      get "/rails/mailers/notifier/foo?name=Ruby&part=text%2Fhtml"
+      assert_equal 200, last_response.status
+      assert_match %r[<p>Hello, Ruby!</p>], last_response.body
+    end
+
     test "plain text mailer preview with attachment" do
       image_file "pixel.png", "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEWzIioca/JlAAAACklEQVQI12NgAAAAAgAB4iG8MwAAAABJRU5ErkJgggo="