#351

backend/app/controllers/posts_controller.rb

@@ -45,7 +45,9 @@ class PostsController < ApplicationController
         .joins("LEFT JOIN (#{ pt_max_sql }) pt_max ON pt_max.post_id = posts.id")
         .reselect('posts.*', Arel.sql("#{ updated_at_all_sql } AS updated_at_all"))
         .preload(:uploaded_user, :parents, :children,
-                 tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+                 active_post_tags: [:sections,
+                                    { tag: [:deerjikists, :materials,
+                                            { tag_name: :wiki_page }] }])
         .with_attached_thumbnail
 
     q = q.where('posts.url LIKE ?', "%#{ url }%") if url
@@ -97,7 +99,9 @@ class PostsController < ApplicationController
 
   def random
     post = filtered_posts.preload(:uploaded_user, :parents, :children,
-                                  tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+                                  active_post_tags: [:sections,
+                                                     { tag: [:deerjikists, :materials,
+                                                             { tag_name: :wiki_page }] }])
                          .with_attached_thumbnail
                          .order('RAND()')
                          .first
@@ -110,7 +114,9 @@ class PostsController < ApplicationController
     post =
         Post
         .includes(:uploaded_user, :parents, :children,
-                  tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+                  active_post_tags: [:sections,
+                                     { tag: [:deerjikists, :materials,
+                                             { tag_name: :wiki_page }] }])
         .with_attached_thumbnail
         .find_by(id: params[:id])
     return head :not_found unless post
@@ -168,6 +174,8 @@ 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 Tag::SectionLiteralParseError
+    render_validation_error fields: { tags: ['タグ区間の記法が不正です．'] }
   rescue ArgumentError => e
     render_validation_error fields: { parent_post_ids: [e.message] }
   rescue ActiveRecord::RecordInvalid => e
@@ -260,6 +268,8 @@ 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 Tag::SectionLiteralParseError
+    render_validation_error fields: { tags: ['タグ区間の記法が不正です．'] }
   rescue ArgumentError => e
     render_validation_error fields: { parent_post_ids: [e.message] }
   rescue ActiveRecord::RecordInvalid => e
@@ -390,7 +400,8 @@ class PostsController < ApplicationController
   end
 
   def build_tag_tree_for post
-    tags = post.tags.reject(&:deprecated?).to_a
+    post_tags = post.active_post_tags.reject { |post_tag| post_tag.tag.deprecated? }
+    tags = post_tags.map(&:tag)
     tag_ids = tags.map(&:id)
 
     implications = TagImplication.where(parent_tag_id: tag_ids, tag_id: tag_ids)
@@ -405,11 +416,9 @@ class PostsController < ApplicationController
     root_ids = tag_ids - child_ids
 
     tags_by_id = tags.index_by(&:id)
-    sections_by_tag_id =
+    sections_by_tag_id = post_tags.to_h { |post_tag|
-        PostTagSection
+      [post_tag.tag_id, post_tag.sections.as_json(only: [:begin_ms, :end_ms])]
-        .where(post_id: post.id, tag_id: tag_ids)
+    }
-        .order(:begin_ms)
-        .group_by(&:tag_id)
 
     memo = { }
 
@@ -418,7 +427,6 @@ class PostsController < ApplicationController
       return nil unless tag
 
       sections = sections_by_tag_id.fetch(tag_id, [])
-                                   .as_json(only: [:begin_ms, :end_ms])
 
       if path.include?(tag_id)
         return TagRepr.inline(tag).merge(children: [], sections:)
@@ -578,7 +586,7 @@ class PostsController < ApplicationController
   end
 
   def section_literal section
-    "[#{ Post.ms_to_time(section[0]) }-#{ Post.ms_to_time(section[1]) }]"
+    "[#{ Post.ms_to_time(section[0]) }-#{ section[1] ? Post.ms_to_time(section[1]) : '' }]"
   end
 
   def post_conflict_json post:, base_version_no:, base_snapshot:,

backend/app/models/post.rb

@@ -86,7 +86,7 @@ class Post < ApplicationRecord
   end
 
   def self.section_literal section
-    "[#{ Post.ms_to_time(section.begin_ms) }-#{ Post.ms_to_time(section.end_ms) }]"
+    "[#{ Post.ms_to_time(section.begin_ms) }-#{ section.end_ms ? Post.ms_to_time(section.end_ms) : '' }]"
   end
 
   def self.ms_to_time ms

backend/app/models/post_tag_section.rb

@@ -15,6 +15,6 @@ class PostTagSection < ApplicationRecord
   validates :begin_ms, presence: true,
                        numericality: { only_integer: true, greater_than_or_equal_to: 0 }
 
-  validates :end_ms, presence: true,
+  validates :end_ms, numericality: { only_integer: true, greater_than: :begin_ms },
-                     numericality: { only_integer: true, greater_than: :begin_ms }
+                     allow_nil: true
 end

backend/app/models/tag.rb

@@ -17,6 +17,16 @@ class Tag < ApplicationRecord
     end
   end
 
+  class SectionLiteralParseError < ArgumentError
+    attr_reader :tag_name, :literal
+
+    def initialize tag_name, literal
+      @tag_name = tag_name
+      @literal = literal
+      super("invalid section literal for tag #{ tag_name }: #{ literal }")
+    end
+  end
+
   has_many :post_tags, inverse_of: :tag
   has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :tag
   has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
@@ -113,20 +123,22 @@ class Tag < ApplicationRecord
 
     sections = { }
     tags = tag_names.map do |name|
+      raw_name = name
       pf, cat = CATEGORY_PREFIXES.find { |p, _| name.downcase.start_with?(p) } || ['', nil]
 
       name = name.sub(/\A#{ pf }/i, '')
 
       sections_by_tag = []
-      while n = name.sub!(/^(\S*?)\[([0-9:.]*?)-([0-9:.]*?)\](\S*?)$/, '\1\4 \2 \3')
+      while (match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/))
-        name, *section_raw = n.split
+        name = "#{ match[1] }#{ match[4] }"
+        sections_by_tag << normalise_section_range!(
+            begin_raw: match[2],
+            end_raw: match[3],
+            tag_name: name)
+      end
 
-        begin_ms, end_ms = section_raw.map { time_to_ms(_1) }
+      if name.include?('[') || name.include?(']')
-        next if begin_ms == end_ms
+        raise SectionLiteralParseError.new(raw_name, raw_name)
-
-        begin_ms, end_ms = end_ms, begin_ms if begin_ms > end_ms
-
-        sections_by_tag << [begin_ms, end_ms]
       end
 
       name = TagName.canonicalise(name).first
@@ -141,6 +153,7 @@ class Tag < ApplicationRecord
 
         sections[tag.id] ||= []
         sections[tag.id].concat(sections_by_tag)
+        sections[tag.id] = merge_section_ranges(sections[tag.id])
       end
     end
 
@@ -178,6 +191,45 @@ class Tag < ApplicationRecord
     (result + tags).uniq { |t| t.id }
   end
 
+  def self.normalise_section_range! begin_raw:, end_raw:, tag_name:
+    begin_ms = begin_raw.empty? ? 0 : time_to_ms!(begin_raw, tag_name:)
+    end_ms = end_raw.empty? ? nil : time_to_ms!(end_raw, tag_name:)
+
+    if end_ms
+      begin_ms, end_ms = end_ms, begin_ms if begin_ms > end_ms
+      end_ms = begin_ms + 1 if begin_ms == end_ms
+    end
+
+    [begin_ms, end_ms]
+  end
+
+  def self.merge_section_ranges ranges
+    sorted_ranges = ranges.sort_by { |begin_ms, end_ms| [begin_ms, end_ms || Float::INFINITY] }
+    merged = []
+
+    sorted_ranges.each do |begin_ms, end_ms|
+      if merged.empty?
+        merged << [begin_ms, end_ms]
+        next
+      end
+
+      last_begin_ms, last_end_ms = merged[-1]
+      if last_end_ms.nil? || begin_ms <= last_end_ms
+        merged[-1] = [last_begin_ms, merge_section_end(last_end_ms, end_ms)]
+      else
+        merged << [begin_ms, end_ms]
+      end
+    end
+
+    merged
+  end
+
+  def self.merge_section_end left_end_ms, right_end_ms
+    return nil if left_end_ms.nil? || right_end_ms.nil?
+
+    [left_end_ms, right_end_ms].max
+  end
+
   def self.find_or_create_by_tag_name! name, category:
     tn = TagName.find_undiscard_or_create_by!(name: name.to_s.strip)
     tn = tn.canonical if tn.canonical_id?
@@ -274,23 +326,30 @@ class Tag < ApplicationRecord
     end
   end
 
-  def self.time_to_ms str
+  def self.time_to_ms! str, tag_name:
-    parts = str.split(':')
+    match =
+        case str
+        when /\A(?<seconds>\d+)(?:\.(?<ms>\d{1,3}))?\z/
+          { hours: nil, minutes: nil, seconds: Regexp.last_match[:seconds],
+            ms: Regexp.last_match[:ms] }
+        when /\A(?<minutes>\d+):(?<seconds>[0-5]?\d)(?:\.(?<ms>\d{1,3}))?\z/
+          { hours: nil, minutes: Regexp.last_match[:minutes],
+            seconds: Regexp.last_match[:seconds],
+            ms: Regexp.last_match[:ms] }
+        when /\A(?<hours>\d+):(?<minutes>[0-5]?\d):(?<seconds>[0-5]?\d)(?:\.(?<ms>\d{1,3}))?\z/
+          { hours: Regexp.last_match[:hours],
+            minutes: Regexp.last_match[:minutes],
+            seconds: Regexp.last_match[:seconds],
+            ms: Regexp.last_match[:ms] }
+        end
 
-    s_part = parts.pop
+    raise SectionLiteralParseError.new(tag_name, str) unless match
-    s, ms = s_part.split('.')
 
-    total_s = s.to_i
+    total_s = match[:seconds].to_i
+    total_s += match[:minutes].to_i * 60 if match[:minutes]
+    total_s += match[:hours].to_i * 3_600 if match[:hours]
 
-    if parts.length >= 1
+    total_s * 1_000 + match[:ms].to_s.ljust(3, '0')[0, 3].to_i
-      total_s += parts.pop.to_i * 60
-    end
-
-    if parts.length >= 1
-      total_s += parts.pop.to_i * 3_600
-    end
-
-    total_s * 1_000 + ms.to_s.ljust(3, '0')[0, 3].to_i
   end
 
   def nico_tags_cannot_be_deprecated

backend/app/representations/post_repr.rb

@@ -18,7 +18,7 @@ module PostRepr
 
   def base post, current_user = nil
     json = common(post)
-    json['tags'] = tag_json(post.tags)
+    json['tags'] = tag_json(post)
     json['uploaded_user'] = post.uploaded_user && UserRepr.base(post.uploaded_user)
     json['viewed'] = current_user ? current_user.viewed?(post) : false
     json
@@ -52,8 +52,16 @@ module PostRepr
                .merge('thumbnail' => thumbnail_url(post))
   end
 
-  def tag_json tags
+  def tag_json post
-    tags.reject(&:deprecated?).map { |tag| TagRepr.inline(tag) }
+    post
+        .active_post_tags
+        .reject { _1.tag.deprecated? }
+        .sort_by { _1.tag.name }
+        .map { |post_tag|
+      TagRepr.inline(post_tag.tag).merge(
+          'children' => [],
+          'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
+    }
   end
 
   def thumbnail_url post

backend/db/migrate/20260622010000_create_post_tag_sections.rb

@@ -4,7 +4,7 @@ class CreatePostTagSections < ActiveRecord::Migration[8.0]
       t.references :post, null: false, foreign_key: true, index: false
       t.references :tag, null: false, foreign_key: true, index: false
       t.integer :begin_ms, null: false
-      t.integer :end_ms, null: false
+      t.integer :end_ms, null: true
       t.timestamps
 
       t.index [:post_id, :begin_ms], name: 'idx_post_tag_sections_post_id_begin_ms'
@@ -12,7 +12,7 @@ class CreatePostTagSections < ActiveRecord::Migration[8.0]
       t.check_constraint 'begin_ms >= 0',
                          name: 'chk_post_tag_sections_begin_ms_natural'
 
-      t.check_constraint 'begin_ms < end_ms',
+      t.check_constraint 'end_ms IS NULL OR begin_ms < end_ms',
                          name: 'chk_post_tag_sections_end_ms_after_begin_ms'
     end
   end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_06_21_000000) do
+ActiveRecord::Schema[8.0].define(version: 2026_06_22_010000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -214,12 +214,12 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_21_000000) do
     t.bigint "post_id", null: false
     t.bigint "tag_id", null: false
     t.integer "begin_ms", null: false
-    t.integer "end_ms", null: false
+    t.integer "end_ms"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["post_id", "begin_ms"], name: "idx_post_tag_sections_post_id_begin_ms"
     t.index ["tag_id"], name: "fk_rails_8be3847903"
-    t.check_constraint "`begin_ms` < `end_ms`", name: "chk_post_tag_sections_end_ms_after_begin_ms"
+    t.check_constraint "(`end_ms` is null) or (`begin_ms` < `end_ms`)", name: "chk_post_tag_sections_end_ms_after_begin_ms"
     t.check_constraint "`begin_ms` >= 0", name: "chk_post_tag_sections_begin_ms_natural"
   end
 
@@ -432,7 +432,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_21_000000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["expires_at"], name: "index_theatre_watching_users_on_expires_at"
-    t.index ["theatre_id", "expires_at"], name: "idx_on_theatre_id_skip_expires_at_4c8de1dd42"
     t.index ["theatre_id", "expires_at"], name: "index_theatre_watching_users_on_theatre_id_and_expires_at"
     t.index ["theatre_id"], name: "index_theatre_watching_users_on_theatre_id"
     t.index ["user_id"], name: "index_theatre_watching_users_on_user_id"

backend/spec/models/post_tag_spec.rb

@@ -25,5 +25,17 @@ RSpec.describe PostTag, type: :model do
 
       expect(post_tag.sections).to be_empty
     end
+
+    it 'allows open-ended sections' do
+      post_tag = create(:post_tag)
+      section = create(:post_tag_section,
+                       post: post_tag.post,
+                       tag: post_tag.tag,
+                       begin_ms: 1000,
+                       end_ms: nil)
+
+      expect(section).to be_valid
+      expect(post_tag.sections).to contain_exactly(section)
+    end
   end
 end

backend/spec/models/tag_spec.rb

@@ -19,6 +19,85 @@ RSpec.describe Tag, type: :model do
         expect(error.tag_names).to eq([deprecated_tag.name])
       }
     end
+
+    it 'rejects invalid section literals instead of treating them as zero' do
+      expect {
+        described_class.normalise_tags!(
+          ['normalise_invalid_section[1:aa-2:00]'],
+          with_sections: true
+        )
+      }.to raise_error(Tag::SectionLiteralParseError)
+    end
+
+    it 'parses open-ended section literals' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[1:00-]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
+    end
+
+    it 'parses omitted begin as zero' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[-1:00]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[0, 60_000]])
+    end
+
+    it 'parses fully open section literals as zero to end-of-video' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[-]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[0, nil]])
+    end
+
+    it 'expands zero-width sections to one millisecond' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[1:00-1:00]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, 60_001]])
+    end
+
+    it 'swaps reversed section boundaries' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[2:00-1:00]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, 120_000]])
+    end
+
+    it 'merges open-ended sections over later bounded sections' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[1:00-][2:00-3:00]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
+    end
+
+    it 'merges adjacent bounded and open-ended sections' do
+      result = described_class.normalise_tags!(
+        ['伊地知ニジカ[1:00-3:00][3:00-]'],
+        with_sections: true
+      )
+
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
+      expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
+    end
   end
 
   describe '.expand_parent_tags' do

backend/spec/requests/posts_spec.rb

@@ -127,6 +127,22 @@ RSpec.describe 'Posts API', type: :request do
       expect(all_tag_names).to include("spec_tag")
     end
 
+    it 'keeps children and sections keys in non-detail tag responses' do
+      PostTagSection.create!(post: hit_post, tag:, begin_ms: 1_000, end_ms: nil)
+
+      get '/posts'
+
+      expect(response).to have_http_status(:ok)
+
+      hit_json = json.fetch('posts').find { |post| post['id'] == hit_post.id }
+      tag_json = hit_json.fetch('tags').find { |item| item['name'] == 'spec_tag' }
+
+      expect(tag_json.fetch('children')).to eq([])
+      expect(tag_json.fetch('sections')).to eq([
+        { 'begin_ms' => 1_000, 'end_ms' => nil }
+      ])
+    end
+
     context "when q is provided" do
       it "filters posts by q (hit case)" do
         get "/posts", params: { tags: "spec_tag" }
@@ -767,6 +783,87 @@ RSpec.describe 'Posts API', type: :request do
       expect(saved_names).not_to include('deprecated_parent', 'deprecated_grandparent')
     end
 
+    it 'returns validation error for an invalid section literal' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'invalid section literal',
+        url: 'https://example.com/invalid-section-literal',
+        tags: 'spec_tag[1:aa-2:00]',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json).to include(
+        'type' => 'validation_error',
+        'message' => '入力内容を確認してください．'
+      )
+      expect(json.fetch('errors')).to include(
+        'tags' => ['タグ区間の記法が不正です．']
+      )
+    end
+
+    it 'saves open-ended sections with end_ms NULL' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'open ended section literal',
+        url: 'https://example.com/open-ended-section-literal',
+        tags: '伊地知ニジカ[1:00-]',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+
+      created_post = Post.find(json.fetch('id'))
+      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
+      section = PostTagSection.find_by!(post: created_post, tag:)
+
+      expect(section.begin_ms).to eq(60_000)
+      expect(section.end_ms).to be_nil
+    end
+
+    it 'treats [-] as [0:00-] and saves end_ms NULL' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'fully open section literal',
+        url: 'https://example.com/fully-open-section-literal',
+        tags: '伊地知ニジカ[-]',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+
+      created_post = Post.find(json.fetch('id'))
+      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
+      section = PostTagSection.find_by!(post: created_post, tag:)
+
+      expect(section.begin_ms).to eq(0)
+      expect(section.end_ms).to be_nil
+    end
+
+    it 'returns end_ms null for open-ended sections in show response' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'show open ended section literal',
+        url: 'https://example.com/show-open-ended-section-literal',
+        tags: '伊地知ニジカ[1:00-]',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+
+      get "/posts/#{ json.fetch('id') }"
+
+      expect(response).to have_http_status(:ok)
+      tag_json = json.fetch('tags').find { |item| item['name'] == '伊地知ニジカ' }
+      expect(tag_json.fetch('sections')).to eq([
+        { 'begin_ms' => 60_000, 'end_ms' => nil }
+      ])
+    end
+
     context "when nico tag already exists in tags" do
       before do
         Tag.find_undiscard_or_create_by!(

frontend/src/components/PostEditForm.tsx

@@ -33,7 +33,7 @@ const tagsToStr = (tags: TagWithSections[]): string => {
 
   return [...(new Set (result.map (t =>
       `${ t.name }${ t.sections
-		     .map (s => `[${ msToTime (s.beginMs) }-${ msToTime (s.endMs) }]`)
+		     .map (s => `[${ msToTime (s.beginMs) }-${ s.endMs == null ? '' : msToTime (s.endMs) }]`)
 		     .join ('') }`)))].join (' ')
 }
 

frontend/src/types.ts

@@ -221,7 +221,7 @@ export type TagVersion = {
     createdByUser:          { id: number; name: string | null } | null }
 
 export type TagWithSections = Tag & { sections: { beginMs:  number
-						  endMs:    number }[]
+						  endMs:    number | null }[]
 			              children: TagWithSections[] }
 
 export type Theatre = {