#76

Reviewed-on: #382

backend/app/controllers/posts_controller.rb

@@ -140,10 +140,11 @@ class PostsController < ApplicationController
     original_created_from = params[:original_created_from]
     original_created_before = params[:original_created_before]
     parent_post_ids = parse_parent_post_ids
+    resized_thumbnail = thumbnail.present? ? Post.resized_thumbnail_attachment(thumbnail) : nil
 
     post = Post.new(title:, url:, thumbnail_base: nil, uploaded_user: current_user,
                     original_created_from:, original_created_before:)
-    post.thumbnail.attach(thumbnail) if thumbnail.present?
+    post.thumbnail.attach(resized_thumbnail) if resized_thumbnail
 
     ApplicationRecord.transaction do
       post.save!
@@ -156,8 +157,6 @@ class PostsController < ApplicationController
 
       sync_parent_posts!(post, parent_post_ids)
 
-      post.resized_thumbnail!
-
       PostVersionRecorder.record!(post:, event_type: :create, created_by_user: current_user)
     end
 
@@ -167,6 +166,8 @@ class PostsController < ApplicationController
     render_validation_error fields: { tags: 'ニコニコ・タグは直接指定できません．' }
   rescue Tag::DeprecatedTagNormalisationError
     render_unprocessable_entity '廃止済みタグは付与できません．', field: :tags
+  rescue MiniMagick::Error
+    render_validation_error fields: { thumbnail: ['サムネイル画像の変換に失敗しました．'] }
   rescue ArgumentError => e
     render_validation_error fields: { parent_post_ids: [e.message] }
   rescue ActiveRecord::RecordInvalid => e

backend/app/controllers/tags_controller.rb

@@ -245,10 +245,7 @@ class TagsController < ApplicationController
     return render_unprocessable_entity('カテゴリは必須です．', field: :category) if category.blank?
     return render_unprocessable_entity '廃止状態は必須です．', field: :deprecated unless params.key?(:deprecated)
 
-    if (name != tag.name &&
-        tag.in?([Tag.tagme, Tag.bot, Tag.no_deerjikist, Tag.video, Tag.niconico]))
-      return render_unprocessable_entity 'システム・タグの名称は変更できません．', field: :name
-    end
+    return unless validate_tag_rename(tag, name)
 
     alias_names = params[:aliases].to_s.split.uniq
     parent_names = params[:parent_tags].to_s.split.uniq
@@ -274,7 +271,7 @@ class TagsController < ApplicationController
       else
         tag.update!(category:, deprecated_at: deprecated ? Time.current : nil)
       end
-      tag.tag_name.update!(name:)
+      rename_tag_name!(tag, name) if name_changed
 
       alias_names << old_name if name_changed
       alias_names.delete(name)
@@ -310,6 +307,8 @@ class TagsController < ApplicationController
       return render_unprocessable_entity 'ニコタグは廃止できません．', field: :deprecated
     end
 
+    return unless validate_tag_rename(tag, name)
+
     if tag.nico? || (category.present? && category == 'nico')
       return render_unprocessable_entity 'ニコタグは変更できません．', field: :category
     end
@@ -321,7 +320,7 @@ class TagsController < ApplicationController
       name_changed = name.present? && name != old_name
       wiki_page = tag.tag_name.wiki_page if name_changed
 
-      tag.tag_name.update!(name:) if name.present?
+      rename_tag_name!(tag, name) if name_changed
       tag.update!(category:) if category.present?
       if deprecated_given && tag.deprecated? != deprecated
         tag.update!(deprecated_at: deprecated ? Time.current : nil)
@@ -535,6 +534,67 @@ class TagsController < ApplicationController
         created_by_user:)
   end
 
+  def validate_tag_rename tag, name
+    return true if name.blank? || name == tag.name
+
+    if tag.in?([Tag.tagme, Tag.bot, Tag.no_deerjikist, Tag.video, Tag.niconico])
+      render_unprocessable_entity 'システム・タグの名称は変更できません．', field: :name
+      return false
+    end
+
+    target_tag_name = TagName.with_discarded.find_by(name:)
+    return true if target_tag_name.nil?
+    return true if target_tag_name.canonical_id?
+
+    render_unprocessable_entity 'その名前は既に使はれてゐます．', field: :name
+    false
+  end
+
+  def rename_tag_name! tag, name
+    return if name == tag.name
+
+    current_tag_name = tag.tag_name
+    target_tag_name = TagName.with_discarded.find_by(name:)
+
+    if target_tag_name.nil?
+      current_tag_name.update!(name:)
+      return
+    end
+
+    promote_tag_alias!(
+        tag,
+        current_tag_name:,
+        promoted_tag_name: target_tag_name)
+  end
+
+  def promote_tag_alias! tag, current_tag_name:, promoted_tag_name:
+    old_owner_tag = promoted_tag_name.canonical&.tag
+
+    if old_owner_tag && old_owner_tag != tag
+      TagVersioning.ensure_snapshot!(old_owner_tag, created_by_user: current_user)
+    end
+
+    promoted_tag_name.undiscard! if promoted_tag_name.discarded?
+    promoted_tag_name.update!(canonical: nil)
+
+    TagName.with_discarded
+           .where(canonical_id: current_tag_name.id)
+           .where.not(id: promoted_tag_name.id)
+           .find_each do |alias_tag_name|
+      alias_tag_name.update!(canonical: promoted_tag_name)
+    end
+
+    current_tag_name.wiki_page&.update!(tag_name: promoted_tag_name)
+    tag.update!(tag_name: promoted_tag_name)
+    current_tag_name.association(:wiki_page).reset
+    current_tag_name.association(:tag).reset
+    current_tag_name.reload.update!(canonical: promoted_tag_name)
+
+    return unless old_owner_tag && old_owner_tag != tag
+
+    record_tag_version!(old_owner_tag.reload, event_type: :update, created_by_user: current_user)
+  end
+
   def update_aliases! tag, alias_names
     alias_names = alias_names.uniq
 

backend/app/models/post.rb

@@ -1,5 +1,19 @@
 class Post < ApplicationRecord
   require 'mini_magick'
+  require 'stringio'
+
+  def self.resized_thumbnail_attachment(upload)
+    upload.rewind
+    image = MiniMagick::Image.read(upload.read)
+    image.resize '180x180'
+    image.format 'jpg'
+
+    { io: StringIO.new(image.to_blob),
+      filename: 'resized_thumbnail.jpg',
+      content_type: 'image/jpeg' }
+  ensure
+    upload.rewind
+  end
 
   belongs_to :uploaded_user, class_name: 'User', optional: true
 
@@ -87,12 +101,7 @@ class Post < ApplicationRecord
   def resized_thumbnail!
     return unless thumbnail.attached?
 
-    image = MiniMagick::Image.read(thumbnail.download)
-    image.resize '180x180'
-    thumbnail.purge
-    thumbnail.attach(io:            File.open(image.path),
-                     filename:      'resized_thumbnail.jpg',
-                     content_type:  'image/jpeg')
+    thumbnail.attach(self.class.resized_thumbnail_attachment(StringIO.new(thumbnail.download)))
   end
 
   private

backend/app/models/tag_implication.rb

@@ -6,6 +6,7 @@ class TagImplication < ApplicationRecord
   validates :parent_tag_id, presence: true
 
   validate :parent_tag_mustnt_be_itself
+  validate :parent_tag_mustnt_create_cycle
 
   private
 
@@ -14,4 +15,27 @@ class TagImplication < ApplicationRecord
       errors.add :parent_tag_id, '親タグは子タグと同一であってはなりません．'
     end
   end
+
+  def parent_tag_mustnt_create_cycle
+    return if tag_id.blank? || parent_tag_id.blank?
+    return if errors[:parent_tag_id].present?
+
+    seen = { }
+    stack = [parent_tag_id]
+
+    until stack.empty?
+      current_id = stack.pop
+      next if seen[current_id]
+
+      seen[current_id] = true
+
+      if current_id == tag_id
+        errors.add :parent_tag_id, '親タグに子孫タグを指定すると循環します．'
+        errors.add :base, 'タグの親子関係が循環します．'
+        return
+      end
+
+      stack.concat(TagImplication.where(tag_id: current_id).pluck(:parent_tag_id))
+    end
+  end
 end

backend/spec/models/tag_implication_spec.rb

@@ -0,0 +1,36 @@
+require 'rails_helper'
+
+RSpec.describe TagImplication, type: :model do
+  it 'rejects a parent tag that would create a cycle' do
+    child = create(:tag, name: 'tag_implication_cycle_child')
+    parent = create(:tag, name: 'tag_implication_cycle_parent')
+
+    described_class.create!(tag: child, parent_tag: parent)
+
+    implication = described_class.new(tag: parent, parent_tag: child)
+
+    expect(implication).not_to be_valid
+    expect(implication.errors[:parent_tag_id]).to include(
+      '親タグに子孫タグを指定すると循環します．'
+    )
+    expect(implication.errors[:base]).to be_present
+  end
+
+  it 'terminates even when existing data already contains a cycle' do
+    child = create(:tag, name: 'tag_implication_existing_cycle_child')
+    parent = create(:tag, name: 'tag_implication_existing_cycle_parent')
+    ancestor = create(:tag, name: 'tag_implication_existing_cycle_ancestor')
+
+    described_class.create!(tag: parent, parent_tag: ancestor)
+    described_class.insert_all!(
+      [
+        { tag_id: ancestor.id, parent_tag_id: parent.id,
+          created_at: Time.current, updated_at: Time.current }
+      ]
+    )
+
+    implication = described_class.new(tag: child, parent_tag: parent)
+
+    expect(implication).to be_valid
+  end
+end

backend/spec/models/tag_spec.rb

@@ -54,7 +54,17 @@ RSpec.describe Tag, type: :model do
       first = create(:tag, name: 'expand_cycle_first')
       second = create(:tag, name: 'expand_cycle_second')
       TagImplication.create!(tag: first, parent_tag: second)
-      TagImplication.create!(tag: second, parent_tag: first)
+      now = Time.current
+      TagImplication.insert_all!(
+        [
+          {
+            tag_id: second.id,
+            parent_tag_id: first.id,
+            created_at: now,
+            updated_at: now
+          }
+        ]
+      )
 
       expect(described_class.expand_parent_tags([first])).to contain_exactly(first, second)
     end

backend/spec/requests/posts_spec.rb

@@ -1,4 +1,5 @@
 require 'rails_helper'
+require 'base64'
 require 'set'
 
 include ActiveSupport::Testing::TimeHelpers
@@ -8,6 +9,11 @@ RSpec.describe 'Posts API', type: :request do
   # resized_thumbnail! が MiniMagick 依存でコケやすいので request spec ではスタブしとくのが無難。
   before do
     allow_any_instance_of(Post).to receive(:resized_thumbnail!).and_return(true)
+    allow(Post).to receive(:resized_thumbnail_attachment).and_return(
+      io: StringIO.new('dummy'),
+      filename: 'resized_thumbnail.jpg',
+      content_type: 'image/jpeg'
+    )
   end
 
   def create_nico_tag!(name)
@@ -19,6 +25,18 @@ RSpec.describe 'Posts API', type: :request do
     Rack::Test::UploadedFile.new(StringIO.new('dummy'), 'image/jpeg', original_filename: 'dummy.jpg')
   end
 
+  def real_thumbnail_upload
+    gif =
+        Base64.decode64(
+            'R0lGODdhAQABAIABAP///wAAACwAAAAAAQABAAACAkQBADs=')
+
+    Rack::Test::UploadedFile.new(
+      StringIO.new(gif),
+      'image/gif',
+      original_filename: 'thumbnail.gif'
+    )
+  end
+
   def post_write_params params = { }
     { parent_post_ids: '' }.merge(params)
   end
@@ -696,6 +714,66 @@ RSpec.describe 'Posts API', type: :request do
       expect(json['tags'][0]).to have_key('name')
     end
 
+    it '201 when posting manually with a thumbnail' do
+      sign_in_as(member)
+      allow(Post).to receive(:resized_thumbnail_attachment).and_call_original
+
+      post '/posts', params: post_write_params(
+        title: 'thumbnail post',
+        url: 'https://example.com/thumbnail-post',
+        tags: 'spec_tag',
+        thumbnail: real_thumbnail_upload
+      )
+
+      expect(response).to have_http_status(:created)
+      post_record = Post.find(json.fetch('id'))
+      expect(post_record.thumbnail).to be_attached
+      expect(post_record.thumbnail.blob.content_type).to eq('image/jpeg')
+      expect { post_record.thumbnail.download }.not_to raise_error
+    end
+
+    it 'resizes the thumbnail before the create transaction begins' do
+      sign_in_as(member)
+
+      open_transactions = []
+      baseline_open_transactions = Post.connection.open_transactions
+      allow(Post).to receive(:resized_thumbnail_attachment) do |_upload|
+        open_transactions << Post.connection.open_transactions
+        { io: StringIO.new('dummy'),
+          filename: 'resized_thumbnail.jpg',
+          content_type: 'image/jpeg' }
+      end
+
+      post '/posts', params: post_write_params(
+        title: 'transaction post',
+        url: 'https://example.com/transaction-post',
+        tags: 'spec_tag',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+      expect(open_transactions).to eq([baseline_open_transactions])
+    end
+
+    it 'returns 422 and does not create a post when thumbnail resize fails' do
+      sign_in_as(member)
+      allow(Post).to receive(:resized_thumbnail_attachment).and_raise(MiniMagick::Error)
+
+      expect {
+        post '/posts', params: post_write_params(
+          title: 'broken thumbnail post',
+          url: 'https://example.com/broken-thumbnail-post',
+          tags: 'spec_tag',
+          thumbnail: dummy_upload
+        )
+      }.not_to change(Post, :count)
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'thumbnail' => ['サムネイル画像の変換に失敗しました．']
+      )
+    end
+
     it '201 and creates post + tags when member and tags have aliases' do
       sign_in_as(member)
 

backend/spec/requests/tag_children_spec.rb

@@ -56,6 +56,17 @@ RSpec.describe "TagChildren", type: :request do
 
         expect(response).to have_http_status(:no_content)
       end
+
+      it 'returns 422 and does not create relation when the new link makes a cycle' do
+        TagImplication.create!(tag: parent, parent_tag: child)
+
+        expect {
+          do_request
+        }.not_to change(TagImplication, :count)
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(TagImplication.where(tag: child, parent_tag: parent)).not_to exist
+      end
     end
 
     context "when Tag.find raises (invalid ids)" do

backend/spec/requests/tags_spec.rb

@@ -581,6 +581,58 @@ RSpec.describe 'Tags API', type: :request do
         expect(response).to have_http_status(:ok)
         expect(wiki_page.reload.wiki_versions.count).to eq(before_wiki_version_count)
       end
+
+      it 'full update で旧名 alias が残った tag を PATCH で旧名へ戻せる' do
+        put "/tags/#{ tag.id }", params: {
+          name: 'patch_roundtrip_target',
+          category: 'general',
+          aliases: 'unko',
+          parent_tags: '',
+          deprecated: '0',
+        }
+
+        expect(response).to have_http_status(:ok)
+        expect(TagName.find_by!(name: 'spec_tag').canonical).to eq(tag.reload.tag_name)
+
+        patch "/tags/#{ tag.id }", params: { name: 'spec_tag' }
+
+        expect(response).to have_http_status(:ok)
+
+        tag.reload
+
+        expect(tag.name).to eq('spec_tag')
+        expect(tag.tag_name.canonical_id).to be_nil
+        expect(TagName.find_by!(name: 'patch_roundtrip_target').canonical).to eq(tag.tag_name)
+      end
+
+      it '別 tag の正規名には変更できない' do
+        wiki_page =
+            Wiki::Commit.create_content!(
+                tag_name: tag.tag_name,
+                body: 'patch collision wiki',
+                created_by_user: member_user,
+                message: 'init')
+
+        patch "/tags/#{ tag.id }", params: { name: 'unknown' }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json.fetch('errors')).to include(
+          'name' => ['その名前は既に使はれてゐます．']
+        )
+
+        expect(tag.reload.name).to eq('spec_tag')
+        expect(tag.tag_name.aliases.map(&:name)).to contain_exactly('unko')
+        expect(wiki_page.reload.tag_name).to eq(tag.tag_name)
+      end
+
+      it 'system tag の name は変更できない' do
+        system_tag = Tag.bot
+
+        patch "/tags/#{ system_tag.id }", params: { name: 'patch_system_tag_renamed' }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(system_tag.reload.name).to eq('bot操作')
+      end
     end
   end
 
@@ -745,7 +797,17 @@ RSpec.describe 'Tags API', type: :request do
       )
       TagImplication.create!(tag: first, parent_tag: root_material)
       TagImplication.create!(tag: second, parent_tag: first)
-      TagImplication.create!(tag: first, parent_tag: second)
+      now = Time.current
+      TagImplication.insert_all!(
+        [
+          {
+            tag_id: first.id,
+            parent_tag_id: second.id,
+            created_at: now,
+            updated_at: now
+          }
+        ]
+      )
 
       get '/tags/with-depth', params: { parent: root_material.id }
 
@@ -1029,6 +1091,42 @@ RSpec.describe 'Tags API', type: :request do
         expect(versions.second.created_by_user_id).to eq(member_user.id)
       end
 
+      it '同じ tag の旧 alias へ戻しても rename できる' do
+        put "/tags/#{ tag.id }", params: {
+          name: 'put_roundtrip_b',
+          category: 'general',
+          aliases: 'unko',
+          parent_tags: '',
+          deprecated: '0',
+        }
+
+        expect(response).to have_http_status(:ok)
+
+        put "/tags/#{ tag.id }", params: {
+          name: 'spec_tag',
+          category: 'general',
+          aliases: 'unko',
+          parent_tags: '',
+          deprecated: '0',
+        }
+
+        expect(response).to have_http_status(:ok)
+
+        tag.reload
+
+        expect(tag.name).to eq('spec_tag')
+        expect(TagName.find_by!(name: 'put_roundtrip_b').canonical).to eq(tag.tag_name)
+        expect(tag.tag_name.aliases.map(&:name)).to contain_exactly('put_roundtrip_b', 'unko')
+        expect(tag.tag_name.aliases.map(&:name)).not_to include('spec_tag')
+        expect(alias_tn.reload.canonical).to eq(tag.tag_name)
+
+        version = tag.tag_versions.order(:version_no).last
+
+        expect(version.event_type).to eq('update')
+        expect(version.name).to eq('spec_tag')
+        expect(version.aliases.split).to contain_exactly('put_roundtrip_b', 'unko')
+      end
+
       it 'parent tag の snapshot も作成する' do
         old_parent = Tag.create!(
           tag_name: TagName.create!(name: 'put_snapshot_old_parent'),
@@ -1153,6 +1251,48 @@ RSpec.describe 'Tags API', type: :request do
         )
       end
 
+      it 'wiki を持つ tag を旧 alias へ戻しても wiki を新 canonical へ移す' do
+        wiki_page =
+            Wiki::Commit.create_content!(
+                tag_name: tag.tag_name,
+                body: 'wiki body before',
+                created_by_user: member_user,
+                message: 'init')
+
+        expect {
+          put "/tags/#{ tag.id }", params: {
+            name: 'put_wiki_roundtrip_b',
+            category: 'general',
+            aliases: 'unko',
+            parent_tags: '',
+            deprecated: '0',
+          }
+
+          put "/tags/#{ tag.id }", params: {
+            name: 'spec_tag',
+            category: 'general',
+            aliases: 'unko',
+            parent_tags: '',
+            deprecated: '0',
+          }
+        }
+            .to change(TagVersion, :count).by(3)
+            .and change(WikiVersion, :count).by(2)
+
+        expect(response).to have_http_status(:ok)
+
+        tag.reload
+
+        expect(wiki_page.reload.tag_name).to eq(tag.tag_name)
+        expect(TagName.find_by!(name: 'put_wiki_roundtrip_b').wiki_page).to be_nil
+        expect(TagName.find_by!(name: 'put_wiki_roundtrip_b').canonical).to eq(tag.tag_name)
+
+        versions = wiki_page.wiki_versions.order(:version_no).last(2)
+
+        expect(versions.map(&:event_type)).to eq(['update', 'update'])
+        expect(versions.map(&:title)).to eq(['put_wiki_roundtrip_b', 'spec_tag'])
+      end
+
       it '別名を他 tag から奪った場合、奪はれた側の tag version も作成する' do
         old_owner = Tag.create!(
           tag_name: TagName.create!(name: 'put_alias_old_owner'),
@@ -1191,9 +1331,49 @@ RSpec.describe 'Tags API', type: :request do
         expect(old_owner_versions.second.aliases.split).not_to include('put_stolen_alias')
       end
 
-      it 'parent_tags に指定すると循環する tag は 422 にする' do
-        pending '#332 で対応予定'
+      it '別 tag の alias 名を rename で奪へる' do
+        old_owner = Tag.create!(
+          tag_name: TagName.create!(name: 'put_alias_collision_owner'),
+          category: :general
+        )
+        stolen_alias = TagName.create!(
+          name: 'put_alias_collision_name',
+          canonical: old_owner.tag_name
+        )
+        wiki_page =
+            Wiki::Commit.create_content!(
+                tag_name: tag.tag_name,
+                body: 'put collision wiki',
+                created_by_user: member_user,
+                message: 'init')
 
+        put "/tags/#{ tag.id }", params: {
+          name: 'put_alias_collision_name',
+          category: 'general',
+          aliases: 'unko',
+          parent_tags: '',
+          deprecated: '0',
+        }
+
+        expect(response).to have_http_status(:ok)
+
+        tag.reload
+        old_owner.reload
+        stolen_alias.reload
+
+        expect(tag.name).to eq('put_alias_collision_name')
+        expect(stolen_alias.canonical_id).to be_nil
+        expect(TagName.find_by!(name: 'spec_tag').canonical).to eq(tag.tag_name)
+        expect(old_owner.tag_name.aliases.map(&:name)).not_to include('put_alias_collision_name')
+
+        old_owner_versions = old_owner.tag_versions.order(:version_no)
+
+        expect(old_owner_versions.last.event_type).to eq('update')
+        expect(old_owner_versions.last.aliases.split).not_to include('put_alias_collision_name')
+        expect(wiki_page.reload.tag_name).to eq(tag.tag_name)
+      end
+
+      it 'parent_tags に指定すると循環する tag は 422 にする' do
         child = Tag.create!(
           tag_name: TagName.create!(name: 'put_cycle_child'),
           category: :general

frontend/src/components/DraggableDroppableTagRow.tsx

@@ -87,10 +87,13 @@ const DraggableDroppableTagRow: FC<Props> = ({ tag, nestLevel, pathKey, parentTa
 	    setDropRef (node)
 	  }}
 	  style={style}
-	  className={cn ('rounded select-none', over && 'ring-2 ring-offset-2')}
+	  className={cn (
+	      'min-w-0 max-w-full overflow-hidden rounded select-none',
+	      over && 'ring-2 ring-offset-2')}
 	  {...attributes}
 	  {...listeners}>
 	<motion.div
+	    className="flex min-w-0 max-w-full items-baseline overflow-hidden"
 	    transition={{ layout: { duration: .2, ease: 'easeOut' } }}
 	    layoutId={`tag-${ sp ? 'sp-' : '' }${ tag.id }`}>
 	  <TagLink tag={tag} nestLevel={nestLevel}/>
@@ -98,4 +101,4 @@ const DraggableDroppableTagRow: FC<Props> = ({ tag, nestLevel, pathKey, parentTa
       </div>)
 }
 
-export default DraggableDroppableTagRow
+export default DraggableDroppableTagRow

frontend/src/components/ResponsiveMarqueeText.tsx

@@ -0,0 +1,243 @@
+import { cn } from '@/lib/utils'
+import { useEffect, useRef, useState } from 'react'
+
+import type { FC } from 'react'
+
+type Props = {
+    text:      string
+    className?: string
+    title?:    string }
+
+const DESKTOP_MARQUEE_MEDIA =
+    '(min-width: 768px) and (hover: hover) and (pointer: fine) and (prefers-reduced-motion: no-preference)'
+const MARQUEE_START_DELAY_MS = 1600
+const MARQUEE_END_HOLD_MS = 2400
+const MARQUEE_SCROLL_PX_PER_SECOND = 43
+const MIN_MARQUEE_OVERFLOW_PX = 1
+
+
+const ResponsiveMarqueeText: FC<Props> = ({ text, className, title }) => {
+  const outerRef = useRef<HTMLSpanElement | null> (null)
+  const staticRef = useRef<HTMLSpanElement | null> (null)
+  const animatedRef = useRef<HTMLSpanElement | null> (null)
+  const animationRef = useRef<Animation | null> (null)
+  const timeoutRef = useRef<number | null> (null)
+  const rafRef = useRef<number | null> (null)
+  const [overflowPx, setOverflowPx] = useState (0)
+  const [desktopMarqueeEnabled, setDesktopMarqueeEnabled] = useState (false)
+  const [active, setActive] = useState (false)
+  const [marqueeVisible, setMarqueeVisible] = useState (false)
+
+  useEffect (() => {
+    const outer = outerRef.current
+    const inner = staticRef.current
+
+    if (!(outer) || !(inner))
+      return
+
+    const measure = () => {
+      const nextOverflow = Math.max (0, Math.ceil (inner.scrollWidth - outer.clientWidth))
+      setOverflowPx (prev => Math.abs (prev - nextOverflow) <= 1 ? prev : nextOverflow)
+    }
+
+    measure ()
+
+    const resizeObserver =
+	typeof ResizeObserver === 'undefined'
+	? null
+	: new ResizeObserver (() => {
+	    measure ()
+	  })
+
+    resizeObserver?.observe (outer)
+    resizeObserver?.observe (inner)
+    addEventListener ('resize', measure)
+
+    return () => {
+      resizeObserver?.disconnect ()
+      removeEventListener ('resize', measure)
+    }
+  }, [text])
+
+  useEffect (() => {
+    if (typeof window === 'undefined' || typeof window.matchMedia !== 'function')
+      return
+
+    const media = window.matchMedia (DESKTOP_MARQUEE_MEDIA)
+    const update = () => {
+      setDesktopMarqueeEnabled (media.matches)
+    }
+
+    update ()
+    media.addEventListener ('change', update)
+
+    return () => {
+      media.removeEventListener ('change', update)
+    }
+  }, [])
+
+  useEffect (() => {
+    const clearScheduled = () => {
+      if (timeoutRef.current != null)
+        {
+          clearTimeout (timeoutRef.current)
+          timeoutRef.current = null
+        }
+      if (rafRef.current != null)
+        {
+          cancelAnimationFrame (rafRef.current)
+          rafRef.current = null
+        }
+      animationRef.current?.cancel ()
+      animationRef.current = null
+    }
+
+    const animated = animatedRef.current
+    const canMarquee = (
+        active
+        && desktopMarqueeEnabled
+        && overflowPx >= MIN_MARQUEE_OVERFLOW_PX
+        && animated != null)
+
+    const resetAnimated = () => {
+      const node = animatedRef.current
+
+      animationRef.current?.cancel ()
+      animationRef.current = null
+      node?.getAnimations?.().forEach (animation => {
+        animation.cancel ()
+      })
+
+      if (!(node))
+        return
+
+      node.style.transition = 'none'
+      node.style.transform = 'translateX(0)'
+    }
+
+    if (!canMarquee)
+      {
+        clearScheduled ()
+        resetAnimated ()
+        setMarqueeVisible (false)
+        return
+      }
+
+    let cancelled = false
+
+    const sleep = (ms: number) =>
+	new Promise<void> (resolve => {
+	  timeoutRef.current = window.setTimeout (() => {
+	    timeoutRef.current = null
+	    resolve ()
+	  }, ms)
+	})
+
+    const runLoop = async () => {
+      while (!cancelled)
+        {
+          resetAnimated ()
+          setMarqueeVisible (true)
+
+          await sleep (MARQUEE_START_DELAY_MS)
+          if (cancelled || !(animatedRef.current))
+            break
+
+          const moveDurationMs =
+	      overflowPx / MARQUEE_SCROLL_PX_PER_SECOND * 1000
+          const node = animatedRef.current
+
+          if (typeof node.animate === 'function')
+            {
+              const animation = node.animate (
+		  [
+		    { transform: 'translateX(0)' },
+		    { transform: `translateX(-${ overflowPx }px)` },
+		  ],
+		  { duration: moveDurationMs, easing: 'linear', fill: 'forwards' })
+              animationRef.current = animation
+              try
+              {
+                await animation.finished
+              }
+              catch
+              {
+                break
+              }
+
+              node.style.transform = `translateX(-${ overflowPx }px)`
+              animation.cancel ()
+              if (animationRef.current === animation)
+                animationRef.current = null
+            }
+          else
+            {
+              node.style.transition = `transform ${ moveDurationMs }ms linear`
+              await new Promise<void> (resolve => {
+                rafRef.current = requestAnimationFrame (() => {
+                  rafRef.current = null
+                  node.style.transform = `translateX(-${ overflowPx }px)`
+                  resolve ()
+                })
+              })
+              await sleep (moveDurationMs)
+              node.style.transition = 'none'
+              node.style.transform = `translateX(-${ overflowPx }px)`
+            }
+
+          if (cancelled)
+            break
+
+          await sleep (MARQUEE_END_HOLD_MS)
+          if (cancelled)
+            break
+
+          resetAnimated ()
+        }
+    }
+
+    void runLoop ()
+
+    return () => {
+      cancelled = true
+      clearScheduled ()
+      resetAnimated ()
+      setMarqueeVisible (false)
+    }
+  }, [active, desktopMarqueeEnabled, overflowPx, text])
+
+  return (
+      <span
+	  ref={outerRef}
+	  title={title ?? text}
+	  onMouseEnter={() => setActive (true)}
+	  onMouseLeave={() => setActive (false)}
+	  onFocus={() => setActive (true)}
+	  onBlur={() => setActive (false)}
+	  className={cn (
+	      'tag-marquee inline-block max-w-full min-w-0 align-bottom',
+	      'whitespace-normal [overflow-wrap:anywhere]',
+	      'md:overflow-hidden md:whitespace-nowrap',
+	      className)}>
+	<span
+	    ref={staticRef}
+	    className={cn (
+		'tag-marquee__static block max-w-full',
+		'whitespace-normal [overflow-wrap:anywhere]',
+		'md:overflow-hidden md:text-ellipsis md:whitespace-nowrap',
+		marqueeVisible && 'md:opacity-0')}>
+	  {text}
+	</span>
+	{overflowPx >= MIN_MARQUEE_OVERFLOW_PX && (
+	    <span
+		ref={animatedRef}
+		aria-hidden="true"
+		className={cn (
+		    'tag-marquee__animated hidden md:block',
+		    marqueeVisible ? 'md:opacity-100' : 'md:opacity-0')}>
+	      {text}
+	    </span>)}
+      </span>)
+}
+
+export default ResponsiveMarqueeText

frontend/src/components/TagLink.tsx

@@ -1,4 +1,5 @@
 import PrefetchLink from '@/components/PrefetchLink'
+import ResponsiveMarqueeText from '@/components/ResponsiveMarqueeText'
 import { LIGHT_COLOUR_SHADE, DARK_COLOUR_SHADE, TAG_COLOUR } from '@/consts'
 import { cn } from '@/lib/utils'
 
@@ -33,6 +34,7 @@ const TagLink: FC<Props> = ({ tag,
 			      withWiki  = true,
 			      withCount = true,
 			      className,
+			      title,
 			      ...props }) => {
   const spanClass = cn (
       `text-${ TAG_COLOUR[tag.category] }-${ LIGHT_COLOUR_SHADE }`,
@@ -41,11 +43,14 @@ const TagLink: FC<Props> = ({ tag,
       spanClass,
       `hover:text-${ TAG_COLOUR[tag.category] }-${ LIGHT_COLOUR_SHADE - 200 }`,
       `dark:hover:text-${ TAG_COLOUR[tag.category] }-${ DARK_COLOUR_SHADE - 200 }`)
+  const textClass = 'group inline-block min-w-0 max-w-full align-bottom'
+  const textTitle = title
+      ?? (tag.matchedAlias == null ? tag.name : `${ tag.matchedAlias } → ${ tag.name }`)
 
   return (
       <>
 	{(linkFlg && withWiki) && (
-	    <span className="mr-1">
+	    <span className="mr-1 shrink-0">
 	      {(tag.materialId != null || tag.hasWiki || tag.hasDeerjikists)
 	       ? (
 		  tag.materialId == null && !(tag.hasDeerjikists)
@@ -100,14 +105,17 @@ const TagLink: FC<Props> = ({ tag,
 	    </span>)}
 	{nestLevel > 0 && (
 	    <span
-		className="ml-1 mr-1"
+		className="ml-1 mr-1 shrink-0"
 		style={{ paddingLeft: `${ (nestLevel - 1) }rem` }}>
 	      ↳
 	    </span>)}
 	{tag.matchedAlias != null && (
 	    <>
-	      <span className={cn (spanClass, className)} {...props}>
-		{tag.matchedAlias}
+	      <span
+		  title={textTitle}
+		  className={cn (spanClass, textClass, className)}
+		  {...props}>
+		<ResponsiveMarqueeText text={tag.matchedAlias} title={textTitle}/>
 	      </span>
 	      <> → </>
 	    </>)}
@@ -115,17 +123,20 @@ const TagLink: FC<Props> = ({ tag,
 	 ? (
 	    <PrefetchLink
 		to={`/posts?${ (new URLSearchParams ({ tags: tag.name })).toString () }`}
-		className={cn (linkClass, className)}
+		title={textTitle}
+		className={cn (linkClass, textClass, className)}
 		{...props}>
-	      {tag.name}
+	      <ResponsiveMarqueeText text={tag.name} title={textTitle}/>
 	    </PrefetchLink>)
 	 : (
-	    <span className={cn (spanClass, className)}
+	    <span
+		  title={textTitle}
+		  className={cn (spanClass, textClass, className)}
 		  {...props}>
-	      {tag.name}
+	      <ResponsiveMarqueeText text={tag.name} title={textTitle}/>
 	    </span>)}
 	{withCount && (
-	    <span className="ml-1">{tag.postCount}</span>)}
+	    <span className="ml-1 shrink-0">{tag.postCount}</span>)}
       </>)
 }
 

frontend/src/components/TagSearchBox.tsx

@@ -20,12 +20,14 @@ const TagSearchBox: FC<Props> = ({ suggestions, activeIndex, onSelect }) => {
 		     rounded shadow">
 	{suggestions.map ((tag, i) => (
 	    <li key={tag.id}
-		className={cn ('px-3 py-2 cursor-pointer hover:bg-gray-300 dark:hover:bg-gray-700', 
+		className={cn ('min-w-0 overflow-hidden px-3 py-2 cursor-pointer hover:bg-gray-300 dark:hover:bg-gray-700',
 			       i === activeIndex && 'bg-gray-300 dark:bg-gray-700')}
 		onMouseDown={() => onSelect (tag)}>
-	      <TagLink tag={tag} linkFlg={false} withWiki={false}/>
+	      <div className="flex min-w-0 max-w-full items-baseline overflow-hidden">
+		<TagLink tag={tag} linkFlg={false} withWiki={false}/>
+	      </div>
 	    </li>))}
       </ul>)
 }
 
-export default TagSearchBox
+export default TagSearchBox

frontend/src/components/TagSidebar.tsx

@@ -64,8 +64,9 @@ const TagSidebar: FC<Props> = ({ posts, onClick }) => {
 	<ul>
 	  {CATEGORIES.flatMap (cat => cat in tags ? (
 	      tags[cat].map (tag => (
-		  <li key={tag.id} className="mb-1">
+		  <li key={tag.id} className="mb-1 min-w-0 max-w-full overflow-hidden">
 		    <motion.div
+			className="flex min-w-0 max-w-full items-baseline overflow-hidden"
 			transition={{ layout: { duration: .2, ease: 'easeOut' } }}
 			layoutId={`tag-${ tag.id }`}>
 		      <TagLink tag={tag} onClick={onClick}/>
@@ -128,4 +129,4 @@ const TagSidebar: FC<Props> = ({ posts, onClick }) => {
       </SidebarComponent>)
 }
 
-export default TagSidebar
+export default TagSidebar

frontend/src/index.css

@@ -132,3 +132,20 @@ body
   0%, 100% { color: #f87171; }
   50% { color: #60a5fa; }
 }
+
+.tag-marquee
+{
+  position: relative;
+}
+
+.tag-marquee__animated
+{
+  position: absolute;
+  inset: 0 auto 0 0;
+  min-width: 100%;
+  width: max-content;
+  opacity: 0;
+  pointer-events: none;
+  white-space: nowrap;
+  will-change: transform;
+}