DEV: Upgrade Discourse to Rails 6 (#8083)

* Adjustments to pass specs on Rails 6.0.0
* Use classic autoloader instead of Zeitwerk
* Update Rails 6.0.0 deprecated methods
* Rails 6.0.0 not allowing column with integer name
* Drop freedom_patches/rails6.rb
* Default value for trigger_transactional_callbacks? is true
* Bump rspec-rails version to 4.0.0.beta2

spec/requests/badges_controller_spec.rb

@@ -39,7 +39,7 @@ describe BadgesController do
     it 'renders rss feed of a badge' do
       get "/badges/#{badge.id}.rss"
       expect(response.status).to eq(200)
-      expect(response.content_type).to eq('application/rss+xml')
+      expect(response.media_type).to eq('application/rss+xml')
     end
   end
 end

spec/requests/groups_controller_spec.rb

@@ -426,7 +426,7 @@ describe GroupsController do
       get "/groups/#{group.name}/posts.rss"
 
       expect(response.status).to eq(200)
-      expect(response.content_type).to eq('application/rss+xml')
+      expect(response.media_type).to eq('application/rss+xml')
     end
   end
 
@@ -435,7 +435,7 @@ describe GroupsController do
       get "/groups/#{group.name}/mentions.rss"
 
       expect(response.status).to eq(200)
-      expect(response.content_type).to eq('application/rss+xml')
+      expect(response.media_type).to eq('application/rss+xml')
     end
 
     it 'fails when disabled' do

spec/requests/list_controller_spec.rb

@@ -320,7 +320,7 @@ RSpec.describe ListController do
     it 'renders latest RSS' do
       get "/latest.rss"
       expect(response.status).to eq(200)
-      expect(response.content_type).to eq('application/rss+xml')
+      expect(response.media_type).to eq('application/rss+xml')
     end
 
     it 'renders links correctly with subfolder' do
@@ -337,14 +337,14 @@ RSpec.describe ListController do
     it 'renders top RSS' do
       get "/top.rss"
       expect(response.status).to eq(200)
-      expect(response.content_type).to eq('application/rss+xml')
+      expect(response.media_type).to eq('application/rss+xml')
     end
 
     TopTopic.periods.each do |period|
       it "renders #{period} top RSS" do
         get "/top/#{period}.rss"
         expect(response.status).to eq(200)
-        expect(response.content_type).to eq('application/rss+xml')
+        expect(response.media_type).to eq('application/rss+xml')
       end
     end
   end
@@ -433,7 +433,7 @@ RSpec.describe ListController do
         it 'renders RSS' do
           get "/c/#{category.slug}.rss"
           expect(response.status).to eq(200)
-          expect(response.content_type).to eq('application/rss+xml')
+          expect(response.media_type).to eq('application/rss+xml')
         end
 
         it "renders RSS in subfolder correctly" do

spec/requests/metadata_controller_spec.rb

@@ -20,7 +20,7 @@ RSpec.describe MetadataController do
 
       get "/manifest.webmanifest"
       expect(response.status).to eq(200)
-      expect(response.content_type).to eq('application/manifest+json')
+      expect(response.media_type).to eq('application/manifest+json')
       manifest = JSON.parse(response.body)
 
       expect(manifest["name"]).to eq(title)
@@ -98,7 +98,7 @@ RSpec.describe MetadataController do
       expect(response.body).to include("/search?q={searchTerms}")
       expect(response.body).to include('image/png')
       expect(response.body).to include(UrlHelper.absolute(upload.url))
-      expect(response.content_type).to eq('application/xml')
+      expect(response.media_type).to eq('application/xml')
     end
   end
 
@@ -121,7 +121,7 @@ RSpec.describe MetadataController do
       expect(response.status).to eq(200)
       expect(response.body).to include("hash_of_app_certificate")
       expect(response.body).to include("com.example.app")
-      expect(response.content_type).to eq('application/json')
+      expect(response.media_type).to eq('application/json')
     end
   end
 
@@ -143,7 +143,7 @@ RSpec.describe MetadataController do
 
       expect(response.status).to eq(200)
       expect(response.body).to include("applinks")
-      expect(response.content_type).to eq('application/json')
+      expect(response.media_type).to eq('application/json')
 
       get "/apple-app-site-association.json"
       expect(response.status).to eq(404)

spec/requests/static_controller_spec.rb

@@ -26,7 +26,7 @@ describe StaticController do
         get '/favicon/proxied'
 
         expect(response.status).to eq(200)
-        expect(response.content_type).to eq('image/png')
+        expect(response.media_type).to eq('image/png')
         expect(response.body.bytesize).to eq(SiteIconManager.favicon.filesize)
       end
 
@@ -36,7 +36,7 @@ describe StaticController do
         get '/favicon/proxied'
 
         expect(response.status).to eq(200)
-        expect(response.content_type).to eq('image/png')
+        expect(response.media_type).to eq('image/png')
         expect(response.body.bytesize).to eq(upload.filesize)
       end
     end
@@ -66,7 +66,7 @@ describe StaticController do
         get '/favicon/proxied'
 
         expect(response.status).to eq(200)
-        expect(response.content_type).to eq('image/png')
+        expect(response.media_type).to eq('image/png')
         expect(response.body.bytesize).to eq(upload.filesize)
       end
     end

spec/requests/topics_controller_spec.rb

@@ -1998,7 +1998,7 @@ RSpec.describe TopicsController do
     it 'renders rss of the topic' do
       get "/t/foo/#{topic.id}.rss"
       expect(response.status).to eq(200)
-      expect(response.content_type).to eq('application/rss+xml')
+      expect(response.media_type).to eq('application/rss+xml')
     end
 
     it 'renders rss of the topic correctly with subfolder' do