Fix generator for mailer (#2735)

Fix filename produced by the mailer generator.

Author: psantos10

features/generator_specs/mailer_specs.feature

@@ -13,10 +13,10 @@ Feature: Mailer generator spec
             create    app/views/posts_mailer/show.text.erb
             create    app/views/posts_mailer/show.html.erb
             invoke  rspec
-            create    spec/mailers/posts_spec.rb
+            create    spec/mailers/posts_mailer_spec.rb
             create    spec/fixtures/posts/index
             create    spec/fixtures/posts/show
-            create    spec/mailers/previews/posts_preview.rb
+            create    spec/mailers/previews/posts_mailer_preview.rb
       """
 
   Scenario: Mailer generator with customized `default-path`
@@ -36,8 +36,8 @@ Feature: Mailer generator spec
             create    app/views/posts_mailer/show.text.erb
             create    app/views/posts_mailer/show.html.erb
             invoke  rspec
-            create    behaviour/mailers/posts_spec.rb
+            create    behaviour/mailers/posts_mailer_spec.rb
             create    behaviour/fixtures/posts/index
             create    behaviour/fixtures/posts/show
-            create    behaviour/mailers/previews/posts_preview.rb
+            create    behaviour/mailers/previews/posts_mailer_preview.rb
       """

lib/generators/rspec/mailer/mailer_generator.rb

@@ -8,7 +8,8 @@ class MailerGenerator < Base
       argument :actions, type: :array, default: [], banner: "method method"
 
       def generate_mailer_spec
-        template "mailer_spec.rb", target_path('mailers', class_path, "#{file_name}_spec.rb")
+        file_suffix = file_name.end_with?('mailer') ? 'spec.rb' : 'mailer_spec.rb'
+        template "mailer_spec.rb", target_path('mailers', class_path, [file_name, file_suffix].join('_'))
       end
 
       def generate_fixtures_files
@@ -21,7 +22,8 @@ def generate_fixtures_files
       def generate_preview_files
         return unless RSpec::Rails::FeatureCheck.has_action_mailer_preview?
 
-        template "preview.rb", target_path("mailers/previews", class_path, "#{file_name}_preview.rb")
+        file_suffix = file_name.end_with?('mailer') ? 'preview.rb' : 'mailer_preview.rb'
+        template "preview.rb", target_path("mailers/previews", class_path, [file_name, file_suffix].join('_'))
       end
     end
   end

lib/generators/rspec/mailer/templates/preview.rb

@@ -1,6 +1,6 @@
 <% module_namespacing do -%>
 # Preview all emails at http://localhost:3000/rails/mailers/<%= file_path %>
-class <%= class_name %>Preview < ActionMailer::Preview
+class <%= class_name %><%= 'Mailer' unless class_name.end_with?('Mailer') %>Preview < ActionMailer::Preview
 <% actions.each do |action| -%>
 
   # Preview this email at http://localhost:3000/rails/mailers/<%= file_path %>/<%= action %>

spec/generators/rspec/mailer/mailer_generator_spec.rb

@@ -6,7 +6,7 @@
   setup_default_destination
 
   describe 'mailer spec' do
-    subject(:filename) { file('spec/mailers/posts_spec.rb') }
+    subject(:filename) { file('spec/mailers/posts_mailer_spec.rb') }
 
     describe 'a spec is created for each action' do
       before do
@@ -66,13 +66,13 @@
       run_generator %w[posts index show]
     end
 
-    subject(:filename) { file('spec/mailers/previews/posts_preview.rb') }
+    subject(:filename) { file('spec/mailers/previews/posts_mailer_preview.rb') }
 
     it "includes the standard boilerplate" do
       expect(
         filename
       ).to(
-        contain(/class PostsPreview < ActionMailer::Preview/)
+        contain(/class PostsMailerPreview < ActionMailer::Preview/)
           .and(contain(/def index/))
           .and(contain(/PostsMailer.index/))
           .and(contain(/def show/))