backend/app/controllers/posts_controller.rb

@@ -97,6 +97,8 @@ class PostsController < ApplicationController
       tags = Tag.normalise_tags(tag_names)
       tags = Tag.expand_parent_tags(tags)
       sync_post_tags!(post, tags)
+
+      post.reload
       render json: post.as_json(include: { tags: { only: [:id, :category, :post_count],
                                                    methods: [:name, :has_wiki] } }),
              status: :created
@@ -136,6 +138,8 @@ class PostsController < ApplicationController
              Tag.normalise_tags(tag_names, with_tagme: false)
       tags = Tag.expand_parent_tags(tags)
       sync_post_tags!(post, tags)
+
+      post.reload
       json = post.as_json
       json['tags'] = build_tag_tree_for(post.tags)
       render json:, status: :ok
@@ -197,6 +201,8 @@ class PostsController < ApplicationController
   end
 
   def filter_posts_by_tags tag_names, match_type
+    tag_names = TagName.canonicalise(tag_names)
+
     posts = Post.joins(tags: :tag_name)
 
     if match_type == 'any'

backend/app/controllers/tags_controller.rb

@@ -18,13 +18,41 @@ class TagsController < ApplicationController
 
     with_nico = !(params[:nico].to_s.strip.downcase.in?(['0', 'false', 'off', 'no']))
 
-    tags = (Tag.joins(:tag_name).includes(:tag_name)
+    alias_rows =
+        TagName
+        .where('name LIKE ?', "#{ q }%")
+        .where.not(canonical_id: nil)
+        .pluck(:canonical_id, :name)
+
+    matched_alias_by_tag_name_id = { }
+    canonical_ids = []
+
+    alias_rows.each do |canonical_id, alias_name|
+      canonical_ids << canonical_id
+      matched_alias_by_tag_name_id[canonical_id] ||= alias_name
+    end
+
+    base = Tag.joins(:tag_name).includes(:tag_name)
+
+    canonical_hit =
+        base
         .where(((with_nico ? '(tags.category = ? AND tag_names.name LIKE ?) OR ' : '') +
                 'tag_names.name LIKE ?'),
                *(with_nico ? ['nico', "nico:#{ q }%"] : []), "#{ q }%")
-            .order(Arel.sql('post_count DESC, tag_names.name ASC'))
-            .limit(20))
-    render json: tags.as_json(only: [:id, :category, :post_count], methods: [:name, :has_wiki])
+
+    tags =
+        if canonical_ids.present?
+          canonical_hit.or(base.where(tag_name_id: canonical_ids.uniq))
+        else
+          canonical_hit
+        end
+
+    tags = tags.order(Arel.sql('post_count DESC, tag_names.name')).limit(20).to_a
+
+    render json: tags.map { |tag|
+      tag.as_json(only: [:id, :category, :post_count], methods: [:name, :has_wiki])
+          .merge(matched_alias: matched_alias_by_tag_name_id[tag.tag_name_id])
+    }
   end
 
   def show

backend/app/models/post.rb

@@ -9,8 +9,8 @@ class Post < ApplicationRecord
   has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
   has_many :tags, through: :active_post_tags
 
-  has_many :user_post_views, dependent: :destroy
-  has_many :post_similarities, dependent: :destroy
+  has_many :user_post_views, dependent: :delete_all
+  has_many :post_similarities, dependent: :delete_all
 
   has_one_attached :thumbnail
 

backend/app/models/tag.rb

@@ -22,6 +22,8 @@ class Tag < ApplicationRecord
            class_name: 'TagImplication', foreign_key: :tag_id, dependent: :destroy
   has_many :parents, through: :reversed_tag_implications, source: :parent_tag
 
+  has_many :tag_similarities, dependent: :delete_all
+
   belongs_to :tag_name
   delegate :name, to: :tag_name, allow_nil: true
   validates :tag_name, presence: true
@@ -72,7 +74,7 @@ class Tag < ApplicationRecord
 
     tags = tag_names.map do |name|
       pf, cat = CATEGORY_PREFIXES.find { |p, _| name.start_with?(p) } || ['', nil]
-      name = name.delete_prefix(pf)
+      name = TagName.canonicalise(name.delete_prefix(pf)).first
       find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
         if cat && tag.category != cat
           tag.update!(category: cat)
@@ -109,6 +111,8 @@ class Tag < ApplicationRecord
 
   def self.find_or_create_by_tag_name! name, category:
     tn = TagName.find_or_create_by!(name: name.to_s.strip)
+    tn = tn.canonical if tn.canonical_id?
+
     Tag.find_or_create_by!(tag_name_id: tn.id) do |t|
       t.category = category
     end
@@ -127,7 +131,7 @@ class Tag < ApplicationRecord
   end
 
   def tag_name_must_be_canonical
-    if tag_name&.canonical_id
+    if tag_name&.canonical_id?
       errors.add :tag_name, 'tag_names へは実体を示す必要があります．'
     end
   end

backend/app/models/tag_name.rb

@@ -9,6 +9,16 @@ class TagName < ApplicationRecord
 
   validate :canonical_must_be_canonical
   validate :alias_name_must_not_have_prefix
+  validate :canonical_must_not_be_present_with_tag_or_wiki_page
+
+  def self.canonicalise names
+    names = Array(names).map { |n| n.to_s.strip }.reject(&:blank?)
+    return [] if names.blank?
+
+    tns = TagName.includes(:canonical).where(name: names).index_by(&:name)
+
+    names.map { |name| tns[name]&.canonical&.name || name }.uniq
+  end
 
   private
 
@@ -23,4 +33,10 @@ class TagName < ApplicationRecord
       errors.add :name, 'エーリアス名にプレフィクスを含むことはできません．'
     end
   end
+
+  def canonical_must_not_be_present_with_tag_or_wiki_page
+    if canonical_id? && (tag || wiki_page)
+      errors.add :canonical, 'タグもしくは Wiki の参照がある名前はエーリアスになれません．'
+    end
+  end
 end

backend/spec/requests/posts_spec.rb

@@ -155,6 +155,7 @@ RSpec.describe 'Posts API', type: :request do
 
   describe 'POST /posts' do
     let(:member) { create(:user, :member) }
+    let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
 
     it '401 when not logged in' do
       sign_out
@@ -201,10 +202,9 @@ RSpec.describe 'Posts API', type: :request do
       expect(json).to include('id', 'title', 'url')
 
       # tags が name を含むこと（API 側の serialization が正しいこと）
-      expect(json).to have_key('tags')
-      expect(json['tags']).to be_an(Array)
-      expect(json['tags'][0]).to have_key('name')
-      expect(json['tags'][0]['name']).to eq('spec_tag')
+      names = json.fetch('tags').map { |t| t['name'] }
+      expect(names).to include('spec_tag')
+      expect(names).not_to include('manko')
     end
 
     context "when nico tag already exists in tags" do