Limit the maximum length of release description

This commit adds the AR validation to the release
model to limit the maximum length of release description
to be less than 1 megabyte.

app/models/release.rb

@@ -24,6 +24,7 @@ class Release < ApplicationRecord
   before_create :set_released_at
 
   validates :project, :tag, presence: true
+  validates :description, length: { maximum: Gitlab::Database::MAX_TEXT_SIZE_LIMIT }, if: :should_validate_description_length?
   validates_associated :milestone_releases, message: -> (_, obj) { obj[:value].map(&:errors).map(&:full_messages).join(",") }
   validates :links, nested_attributes_duplicates: { scope: :release, child_attributes: %i[name url filepath] }
 
@@ -101,6 +102,11 @@ class Release < ApplicationRecord
 
   private
 
+  def should_validate_description_length?
+    description_changed? &&
+      ::Feature.enabled?(:validate_release_description_length, project, default_enabled: :yaml)
+  end
+
   def actual_sha
     sha || actual_tag&.dereferenced_target
   end

config/feature_flags/development/validate_release_description_length.yml

+---
+name: validate_release_description_length
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/60380
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/329192
+milestone: '13.12'
+type: development
+group: group::release
+default_enabled: false

spec/models/release_spec.rb

@@ -38,6 +38,30 @@ RSpec.describe Release do
       end
     end
 
+    context 'when description of a release is longer than the limit' do
+      let(:description) { 'a' * (Gitlab::Database::MAX_TEXT_SIZE_LIMIT + 1) }
+      let(:release) { build(:release, project: project, description: description) }
+
+      it 'creates a validation error' do
+        release.validate
+
+        expect(release.errors.full_messages)
+          .to include("Description is too long (maximum is #{Gitlab::Database::MAX_TEXT_SIZE_LIMIT} characters)")
+      end
+
+      context 'when validate_release_description_length feature flag is disabled' do
+        before do
+          stub_feature_flags(validate_release_description_length: false)
+        end
+
+        it 'does not create a validation error' do
+          release.validate
+
+          expect(release.errors.full_messages).to be_empty
+        end
+      end
+    end
+
     context 'when a release is tied to a milestone for another project' do
       it 'creates a validation error' do
         milestone = build(:milestone, project: create(:project))