Add foreign key to active_storage_attachments for `blob_id` via new migration

We need this in order to be able to add this migration for users that
use ActiveStorage during update their apps from Rails 5.2 to Rails 6.0.

Related to #33405

`rake app:update` should update active_storage

`rake app:update` should execute `rake active_storage:update`
if it is used in the app that is being updated.
It will add new active_storage's migrations to users' apps during update Rails.

Context https://github.com/rails/rails/pull/33405#discussion_r204239399

Also, see a related discussion in the Campfire:
https://3.basecamp.com/3076981/buckets/24956/chats/12416418@1236713081

6 files changed, 31 insertions, 1 deletions

diff --git a/.rubocop.yml b/.rubocop.yml
index 4d2bacde32..dce1a30d9f 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -135,6 +135,7 @@ Style/FrozenStringLiteralComment:
     - 'actionpack/test/**/*.builder'
     - 'actionpack/test/**/*.ruby'
     - 'activestorage/db/migrate/**/*.rb'
+    - 'activestorage/db/update_migrate/**/*.rb'
     - 'actionmailbox/db/migrate/**/*.rb'
     - 'actiontext/db/migrate/**/*.rb'
 
diff --git a/activerecord/lib/active_record/railties/databases.rake b/activerecord/lib/active_record/railties/databases.rake
index d24324ecce..8de06e8466 100644
--- a/activerecord/lib/active_record/railties/databases.rake
+++ b/activerecord/lib/active_record/railties/databases.rake
@@ -407,6 +407,10 @@ namespace :railties do
         if railtie.respond_to?(:paths) && (path = railtie.paths["db/migrate"].first)
           railties[railtie.railtie_name] = path
         end
+
+        unless ENV["MIGRATIONS_PATH"].blank?
+          railties[railtie.railtie_name] = railtie.root + ENV["MIGRATIONS_PATH"]
+        end
       end
 
       on_skip = Proc.new do |name, migration|
diff --git a/activestorage/db/update_migrate/20180723000244_add_foreign_key_constraint_to_active_storage_attachments_for_blob_id.rb b/activestorage/db/update_migrate/20180723000244_add_foreign_key_constraint_to_active_storage_attachments_for_blob_id.rb
new file mode 100644
index 0000000000..6830203cd6
--- /dev/null
+++ b/activestorage/db/update_migrate/20180723000244_add_foreign_key_constraint_to_active_storage_attachments_for_blob_id.rb
@@ -0,0 +1,7 @@
+class AddForeignKeyConstraintToActiveStorageAttachmentsForBlobId < ActiveRecord::Migration[6.0]
+  def up
+    unless foreign_key_exists?(:active_storage_attachments, column: :blob_id)
+      add_foreign_key :active_storage_attachments, :active_storage_blobs, column: :blob_id
+    end
+  end
+end
diff --git a/activestorage/lib/tasks/activestorage.rake b/activestorage/lib/tasks/activestorage.rake
index ac254d717f..6b0469636c 100644
--- a/activestorage/lib/tasks/activestorage.rake
+++ b/activestorage/lib/tasks/activestorage.rake
@@ -12,4 +12,11 @@ namespace :active_storage do
       Rake::Task["app:active_storage:install:migrations"].invoke
     end
   end
+
+  # desc "Copy over the migrations needed to the application upgrading"
+  task update: :environment do
+    ENV["MIGRATIONS_PATH"] = "db/update_migrate"
+
+    Rake::Task["active_storage:install"].invoke
+  end
 end
diff --git a/railties/lib/rails/generators/rails/app/app_generator.rb b/railties/lib/rails/generators/rails/app/app_generator.rb
index e777590be8..5c59566dc2 100644
--- a/railties/lib/rails/generators/rails/app/app_generator.rb
+++ b/railties/lib/rails/generators/rails/app/app_generator.rb
@@ -306,6 +306,13 @@ module Rails
       end
       remove_task :update_bin_files
 
+      def update_active_storage
+        unless skip_active_storage?
+          rails_command "active_storage:update"
+        end
+      end
+      remove_task :update_active_storage
+
       def create_config_files
         build(:config)
       end
diff --git a/railties/lib/rails/tasks/framework.rake b/railties/lib/rails/tasks/framework.rake
index 1a3711c446..2886986865 100644
--- a/railties/lib/rails/tasks/framework.rake
+++ b/railties/lib/rails/tasks/framework.rake
@@ -2,7 +2,7 @@
 
 namespace :app do
   desc "Update configs and some other initially generated files (or use just update:configs or update:bin)"
-  task update: [ "update:configs", "update:bin", "update:upgrade_guide_info" ]
+  task update: [ "update:configs", "update:bin", "update:active_storage", "update:upgrade_guide_info" ]
 
   desc "Applies the template supplied by LOCATION=(/path/to/template) or URL"
   task template: :environment do
@@ -51,6 +51,10 @@ namespace :app do
       Rails::AppUpdater.invoke_from_app_generator :update_bin_files
     end
 
+    task :active_storage do
+      Rails::AppUpdater.invoke_from_app_generator :update_active_storage
+    end
+
     task :upgrade_guide_info do
       Rails::AppUpdater.invoke_from_app_generator :display_upgrade_guide_info
     end