Use URI.join even when S3 enabled (#4652)

app/helpers/routing_helper.rb

@@ -12,6 +12,8 @@ module RoutingHelper
   end
 
   def full_asset_url(source, options = {})
-    Rails.configuration.x.use_s3 ? source : URI.join(root_url, ActionController::Base.helpers.asset_url(source, options)).to_s
+    source = ActionController::Base.helpers.asset_url(source, options) unless Rails.configuration.x.use_s3
+
+    URI.join(root_url, source).to_s
   end
 end

spec/helpers/routing_helper_spec.rb

@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe RoutingHelper, type: :helper do
+  describe '.full_asset_url' do
+    around do |example|
+      use_s3 = Rails.configuration.x.use_s3
+      example.run
+      Rails.configuration.x.use_s3 = use_s3
+    end
+
+    shared_examples 'returns full path URL' do
+      it 'with host' do
+        url = helper.full_asset_url('https://example.com/avatars/000/000/002/original/icon.png')
+
+        expect(url).to eq 'https://example.com/avatars/000/000/002/original/icon.png'
+      end
+
+      it 'without host' do
+        url = helper.full_asset_url('/avatars/original/missing.png', skip_pipeline: true)
+
+        expect(url).to eq 'http://test.host/avatars/original/missing.png'
+      end
+    end
+
+    context 'Do not use S3' do
+      before do
+        Rails.configuration.x.use_s3 = false
+      end
+
+      it_behaves_like 'returns full path URL'
+    end
+
+    context 'Use S3' do
+      before do
+        Rails.configuration.x.use_s3 = true
+      end
+
+      it_behaves_like 'returns full path URL'
+    end
+  end
+end