Extract methods to get tenant subfolder/file paths

We were using the same logic in many different places, so we're
simplifying the code. I'm not convinced about the method names, though,
so we might change them in the future.

Note using this method for the default tenant in the `TenantDiskService`
class resulted in a `//` in the path, which is probably harmless but
very ugly and it also generates a different key than the one we got
until now. I've added an extra test to make sure that isn't the case.

app/models/machine_learning.rb

@@ -89,15 +89,7 @@ class MachineLearning
     end
 
     def tenant_data_folder
-      File.join(tenant_subfolder, "machine_learning", "data").delete_prefix("/")
-    end
-
-    def tenant_subfolder
-      if Tenant.default?
-        ""
-      else
-        File.join("tenants", Tenant.current_schema)
-      end
+      Tenant.path_with_subfolder("machine_learning/data")
     end
 
     def data_output_files

app/models/tenant.rb

@@ -71,6 +71,18 @@ class Tenant < ApplicationRecord
     end
   end
 
+  def self.subfolder_path
+    if default?
+      ""
+    else
+      File.join("tenants", current_schema)
+    end
+  end
+
+  def self.path_with_subfolder(filename_or_folder)
+    File.join(subfolder_path, filename_or_folder).delete_prefix("/")
+  end
+
   def self.default?
     current_schema == "public"
   end

app/views/robots/index.text.erb

@@ -14,8 +14,4 @@ Disallow: /*?*locale-switcher
 Disallow: /*?*filter
 Disallow: user_id
 
-<% if Tenant.default? %>
-Sitemap: <%= "#{root_url}sitemap.xml" %>
-<% else %>
-Sitemap: <%= "#{root_url}tenants/#{Tenant.current_schema}/sitemap.xml" %>
-<% end %>
+Sitemap: <%= "#{root_url}#{Tenant.path_with_subfolder("sitemap.xml")}" %>

config/sitemap.rb

@@ -10,12 +10,7 @@ SitemapGenerator::Sitemap.verbose = false if Rails.env.test?
 
 Tenant.run_on_each do
   SitemapGenerator::Sitemap.default_host = root_url(Tenant.current_url_options)
-
-  if Tenant.default?
-    SitemapGenerator::Sitemap.sitemaps_path = nil
-  else
-    SitemapGenerator::Sitemap.sitemaps_path = "tenants/#{Tenant.current_schema}"
-  end
+  SitemapGenerator::Sitemap.sitemaps_path = Tenant.subfolder_path
 
   SitemapGenerator::Sitemap.create do
     add help_path

lib/active_storage/service/tenant_disk_service.rb

@@ -6,7 +6,7 @@ module ActiveStorage
       if Tenant.default?
         super
       else
-        super.sub(root, File.join(root, "tenants", Tenant.current_schema))
+        super.sub(root, File.join(root, Tenant.subfolder_path))
       end
     end
   end

spec/models/attachable_spec.rb

@@ -5,6 +5,7 @@ describe Attachable do
     file_path = build(:image).file_path
 
     expect(file_path).to include "storage/"
+    expect(file_path).not_to include "storage//"
     expect(file_path).not_to include "tenants"
   end