AI: address review on PR #469

backend/app/controllers/tag_versions_controller.rb

@@ -69,11 +69,8 @@ class TagVersionsController < ApplicationController
 
       parent_tags =
           build_version_values(cur_parent_tag_ids, prev_parent_tag_ids, key: :tag_id)
-          .filter_map do |h|
+          .map do |h|
-            parent = parent_json[h[:tag_id]]
+            { tag: parent_json.fetch(h[:tag_id]),
-            next unless parent
-
-            { tag: parent,
               type: h[:type] }
           end
 

backend/app/models/post_implication.rb

@@ -8,6 +8,7 @@ class PostImplication < ApplicationRecord
   validates :parent_post_id, presence: true
 
   validate :parent_post_mustnt_be_itself
+  validate :parent_post_mustnt_create_cycle
 
   private
 
@@ -16,4 +17,24 @@ class PostImplication < ApplicationRecord
       errors.add :parent_post_id, '親投稿に同じ投稿を設定することはできません．'
     end
   end
+
+  def parent_post_mustnt_create_cycle
+    return if post_id.blank? || parent_post_id.blank?
+    return if errors[:parent_post_id].present?
+
+    ancestor_ids = Set.new
+    frontier_ids = [parent_post_id]
+
+    until frontier_ids.empty?
+      if frontier_ids.include?(post_id)
+        errors.add :parent_post_id, :invalid
+        return
+      end
+
+      ancestor_ids.merge(frontier_ids)
+      frontier_ids = PostImplication.where(post_id: frontier_ids)
+          .distinct.pluck(:parent_post_id)
+          .reject { ancestor_ids.include?(_1) }
+    end
+  end
 end

backend/spec/models/post_implication_spec.rb

@@ -48,4 +48,47 @@ RSpec.describe PostImplication, type: :model do
     expect(duplicate).not_to be_valid
     expect(duplicate.errors[:post_id]).to be_present
   end
+
+  it 'rejects a parent that would create a two-post cycle' do
+    described_class.create!(post: post_record, parent_post:)
+
+    implication = described_class.new(
+        post: parent_post, parent_post: post_record)
+
+    expect(implication).not_to be_valid
+    expect(implication.errors.of_kind?(:parent_post_id, :invalid)).to be true
+  end
+
+  it 'rejects a parent that would create a three-post cycle' do
+    ancestor_post = create(:post)
+    described_class.create!(post: post_record, parent_post:)
+    described_class.create!(post: parent_post, parent_post: ancestor_post)
+
+    implication = described_class.new(
+        post: ancestor_post, parent_post: post_record)
+
+    expect(implication).not_to be_valid
+    expect(implication.errors.of_kind?(:parent_post_id, :invalid)).to be true
+  end
+
+  it 'allows a parent with an ancestor when no cycle would result' do
+    ancestor_post = create(:post)
+    described_class.create!(post: parent_post, parent_post: ancestor_post)
+
+    implication = described_class.new(post: post_record, parent_post:)
+
+    expect(implication).to be_valid
+  end
+
+  it 'terminates when existing ancestors already contain a cycle' do
+    ancestor_post = create(:post)
+    described_class.create!(post: parent_post, parent_post: ancestor_post)
+    legacy_implication = described_class.new(
+        post: ancestor_post, parent_post:)
+    legacy_implication.save!(validate: false)
+
+    implication = described_class.new(post: post_record, parent_post:)
+
+    expect(implication).to be_valid
+  end
 end

backend/spec/requests/tag_versions_spec.rb

@@ -215,36 +215,6 @@ RSpec.describe 'TagVersions API', type: :request do
       expect(first.fetch('created_at')).to eq(t_v1.iso8601)
     end
 
-    [:parent_shared, :parent_new, :parent_old].each do |parent_key|
-      it "omits deleted #{ parent_key } from parent diffs" do
-        deleted_parent = public_send(parent_key)
-        deleted_parent.tag_names.destroy_all
-        deleted_parent.destroy!
-
-        get '/tags/versions', params: { id: tag.id }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('count')).to eq(2)
-
-        versions = json.fetch('versions')
-        expect(versions.map { _1.fetch('version_no') }).to eq([2, 1])
-
-        expected_parents = [
-            [parent_shared.id, 'context'],
-            [parent_new.id, 'added'],
-            [parent_old.id, 'removed']].reject { _1.first == deleted_parent.id }
-        expect(versions.first.fetch('parent_tags').map { |entry|
-          [entry.fetch('tag').fetch('id'), entry.fetch('type')]
-        }).to eq(expected_parents)
-
-        expected_first_parents = [parent_shared.id, parent_old.id]
-            .reject { _1 == deleted_parent.id }.map { [_1, 'added'] }
-        expect(versions.second.fetch('parent_tags').map { |entry|
-          [entry.fetch('tag').fetch('id'), entry.fetch('type')]
-        }).to eq(expected_first_parents)
-      end
-    end
-
     it 'returns empty when the specified tag has no versions' do
       fresh_tag = create(:tag, primary_name: 'no_versions_tag', category: :general)