FEATURE: categories can require topics have a tag from a tag group

In a category's settings, the Tags tab has two new fields to
specify the number of tags that must be added to a topic
from a tag group. When creating a new topic, an error will be
shown to the user if the requirement isn't met.

app/assets/javascripts/discourse/models/category.js.es6

@@ -31,6 +31,13 @@ const Category = RestModel.extend({
     }
   },
 
+  @on("init")
+  setupRequiredTagGroups() {
+    if (this.required_tag_group_name) {
+      this.set("required_tag_groups", [this.required_tag_group_name]);
+    }
+  },
+
   @computed
   availablePermissions() {
     return [
@@ -127,6 +134,10 @@ const Category = RestModel.extend({
         allowed_tags: this.allowed_tags,
         allowed_tag_groups: this.allowed_tag_groups,
         allow_global_tags: this.allow_global_tags,
+        required_tag_group_name: this.required_tag_groups
+          ? this.required_tag_groups[0]
+          : null,
+        min_tags_from_required_group: this.min_tags_from_required_group,
         sort_order: this.sort_order,
         sort_ascending: this.sort_ascending,
         topic_featured_link_allowed: this.topic_featured_link_allowed,

app/assets/javascripts/discourse/templates/components/edit-category-tags.hbs

@@ -24,3 +24,23 @@
 <section class='field'>
   {{i18n 'category.tags_tab_description'}}
 </section>
+
+<section class="field">
+  {{i18n 'category.required_tag_group_description'}}
+</section>
+
+<section class="field with-items">
+  <section class="field-item">
+    <label>{{i18n 'category.min_tags_from_required_group_label'}}</label>
+    {{text-field value=category.min_tags_from_required_group id="category-min-tags-from-group" type="number" min="1"}}
+  </section>
+  <section class="field-item">
+    <label>{{i18n 'category.required_tag_group_label'}}</label>
+    {{tag-group-chooser
+      id="category-required-tag-group"
+      tagGroups=category.required_tag_groups
+      maximum=1
+      filterPlaceholder="category.tag_group_selector_placeholder"
+    }}
+  </section>
+</section>

app/assets/stylesheets/common/base/modal.scss

@@ -268,12 +268,15 @@
   section.field {
     padding: 0.25em 0;
     margin-bottom: 5px;
+    &.with-items {
+      display: flex;
+      align-items: flex-start;
     }
-
-  section.field .field-item {
+    .field-item {
       display: inline-block;
       margin-right: 10px;
     }
+  }
 
   // password reset modal
   .modal-body.forgot-password-modal p {
@@ -446,6 +449,9 @@
       }
     }
   }
+  #category-min-tags-from-group {
+    width: 100px;
+  }
 }
 
 .incoming-email-modal {

app/controllers/categories_controller.rb

@@ -313,6 +313,8 @@ class CategoriesController < ApplicationController
         :navigate_to_first_post_after_read,
         :search_priority,
         :allow_global_tags,
+        :required_tag_group_name,
+        :min_tags_from_required_group,
         custom_fields: [params[:custom_fields].try(:keys)],
         permissions: [*p.try(:keys)],
         allowed_tags: [],

app/models/category.rb

@@ -51,6 +51,7 @@ class Category < ActiveRecord::Base
 
   validates :num_featured_topics, numericality: { only_integer: true, greater_than: 0 }
   validates :search_priority, inclusion: { in: Searchable::PRIORITIES.values }
+  validates :min_tags_from_required_group, numericality: { only_integer: true, greater_than: 0 }
 
   validate :parent_category_validator
   validate :email_in_validator
@@ -93,6 +94,8 @@ class Category < ActiveRecord::Base
   has_many :tags, through: :category_tags
   has_many :category_tag_groups, dependent: :destroy
   has_many :tag_groups, through: :category_tag_groups
+  belongs_to :required_tag_group, class_name: 'TagGroup'
+
   belongs_to :reviewable_by_group, class_name: 'Group'
 
   scope :latest, -> { order('topic_count DESC') }
@@ -555,6 +558,10 @@ class Category < ActiveRecord::Base
     self.tag_groups = TagGroup.where(name: group_names).all.to_a
   end
 
+  def required_tag_group_name=(group_name)
+    self.required_tag_group = group_name ? TagGroup.where(name: group_name).first : nil
+  end
+
   def downcase_email
     self.email_in = (email_in || "").strip.downcase.presence
   end

app/serializers/site_category_serializer.rb

@@ -4,7 +4,9 @@ class SiteCategorySerializer < BasicCategorySerializer
 
   attributes :allowed_tags,
              :allowed_tag_groups,
-             :allow_global_tags
+             :allow_global_tags,
+             :min_tags_from_required_group,
+             :required_tag_group_name
 
   def include_allowed_tags?
     SiteSetting.tagging_enabled
@@ -26,4 +28,8 @@ class SiteCategorySerializer < BasicCategorySerializer
     SiteSetting.tagging_enabled
   end
 
+  def required_tag_group_name
+    object.required_tag_group&.name
+  end
+
 end

config/locales/client.en.yml

@@ -2606,10 +2606,14 @@ en:
       tags_allowed_tags: "Restrict these tags to this category:"
       tags_allowed_tag_groups: "Restrict these tag groups to this category:"
       tags_placeholder: "(Optional) list of allowed tags"
-      tags_tab_description: "Tags and tag groups specified here will only be available in this category and other categories that also specify them. They won't be available for use in other categories."
+      tags_tab_description: "Tags and tag groups specified above will only be available in this category and other categories that also specify them. They won't be available for use in other categories."
       tag_groups_placeholder: "(Optional) list of allowed tag groups"
       manage_tag_groups_link: "Manage tag groups here."
       allow_global_tags_label: "Also allow other tags"
+      tag_group_selector_placeholder: "(Optional) Tag group"
+      required_tag_group_description: "Require new topics to have tags from a tag group:"
+      min_tags_from_required_group_label: 'Num Tags:'
+      required_tag_group_label: "Tag group:"
       topic_featured_link_allowed: "Allow featured links in this category"
       delete: "Delete Category"
       create: "New Category"

config/locales/server.en.yml

@@ -4344,6 +4344,9 @@ en:
       restricted_to:
         one: '"%{tag_name}" is restricted to the "%{category_names}" category'
         other: '"%{tag_name}" is restricted to the following categories: %{category_names}'
+    required_tags_from_group:
+      one: "You must include at least %{count} %{tag_group_name} tag."
+      other: "You must include at least %{count} %{tag_group_name} tags."
   rss_by_tag: "Topics tagged %{tag}"
 
   finish_installation:

db/migrate/20191030155530_add_required_tag_group_to_categories.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class AddRequiredTagGroupToCategories < ActiveRecord::Migration[6.0]
+  def change
+    add_column :categories, :required_tag_group_id, :integer, null: true
+    add_column :categories, :min_tags_from_required_group, :integer, null: false, default: 1
+  end
+end

lib/discourse_tagging.rb

@@ -88,11 +88,8 @@ module DiscourseTagging
           tags = tags + Tag.where(id: missing_parent_tag_ids).all
         end
 
-        # validate minimum required tags for a category
-        if !guardian.is_staff? && category && category.minimum_required_tags > 0 && tags.length < category.minimum_required_tags
-          topic.errors.add(:base, I18n.t("tags.minimum_required_tags", count: category.minimum_required_tags))
-          return false
-        end
+        return false unless validate_min_required_tags_for_category(guardian, topic, category, tags)
+        return false unless validate_required_tags_from_group(guardian, topic, category, tags)
 
         if tags.size == 0
           topic.errors.add(:base, I18n.t("tags.forbidden.invalid", count: new_tag_names.size))
@@ -101,11 +98,8 @@ module DiscourseTagging
 
         topic.tags = tags
       else
-        # validate minimum required tags for a category
-        if !guardian.is_staff? && category && category.minimum_required_tags > 0
-          topic.errors.add(:base, I18n.t("tags.minimum_required_tags", count: category.minimum_required_tags))
-          return false
-        end
+        return false unless validate_min_required_tags_for_category(guardian, topic, category)
+        return false unless validate_required_tags_from_group(guardian, topic, category)
 
         topic.tags = []
       end
@@ -114,6 +108,39 @@ module DiscourseTagging
     true
   end
 
+  def self.validate_min_required_tags_for_category(guardian, topic, category, tags = [])
+    if !guardian.is_staff? &&
+        category &&
+        category.minimum_required_tags > 0 &&
+        tags.length < category.minimum_required_tags
+
+      topic.errors.add(:base, I18n.t("tags.minimum_required_tags", count: category.minimum_required_tags))
+      false
+    else
+      true
+    end
+  end
+
+  def self.validate_required_tags_from_group(guardian, topic, category, tags = [])
+    if !guardian.is_staff? &&
+        category &&
+        category.required_tag_group &&
+        (tags.length < category.min_tags_from_required_group ||
+          category.required_tag_group.tags.where("tags.id in (?)", tags.map(&:id)).count < category.min_tags_from_required_group)
+
+      topic.errors.add(:base,
+        I18n.t(
+          "tags.required_tags_from_group",
+          count: category.min_tags_from_required_group,
+          tag_group_name: category.required_tag_group.name
+        )
+      )
+      false
+    else
+      true
+    end
+  end
+
   # Options:
   #   term: a search term to filter tags by name
   #   category: a Category to which the object being tagged belongs

lib/topic_creator.rb

@@ -147,10 +147,10 @@ class TopicCreator
   def setup_tags(topic)
     if @opts[:tags].blank?
       unless @guardian.is_staff? || !guardian.can_tag?(topic)
-        # Validate minimum required tags for a category
         category = find_category
-        if category.present? && category.minimum_required_tags > 0
-          topic.errors.add(:base, I18n.t("tags.minimum_required_tags", count: category.minimum_required_tags))
+
+        if !DiscourseTagging.validate_min_required_tags_for_category(@guardian, topic, category) ||
+            !DiscourseTagging.validate_required_tags_from_group(@guardian, topic, category)
           rollback_from_errors!(topic)
         end
       end

spec/components/discourse_tagging_spec.rb

@@ -236,6 +236,52 @@ describe DiscourseTagging do
         expect(topic.reload.tags.map(&:name)).to contain_exactly(*[parent_tag, common].map(&:name))
       end
     end
+
+    context "enforces required tags from a tag group" do
+      fab!(:category) { Fabricate(:category) }
+      fab!(:tag_group) { Fabricate(:tag_group) }
+      fab!(:topic) { Fabricate(:topic, category: category) }
+
+      before do
+        tag_group.tags = [tag1, tag2]
+        category.update(
+          required_tag_group: tag_group,
+          min_tags_from_required_group: 1
+        )
+      end
+
+      it "when no tags are present" do
+        valid = DiscourseTagging.tag_topic_by_names(topic, Guardian.new(user), [])
+        expect(valid).to eq(false)
+        expect(topic.errors[:base]&.first).to eq(
+          I18n.t("tags.required_tags_from_group", count: 1, tag_group_name: tag_group.name)
+        )
+      end
+
+      it "when tags are not part of the tag group" do
+        valid = DiscourseTagging.tag_topic_by_names(topic, Guardian.new(user), [tag3.name])
+        expect(valid).to eq(false)
+        expect(topic.errors[:base]&.first).to eq(
+          I18n.t("tags.required_tags_from_group", count: 1, tag_group_name: tag_group.name)
+        )
+      end
+
+      it "when requirement is met" do
+        valid = DiscourseTagging.tag_topic_by_names(topic, Guardian.new(user), [tag1.name])
+        expect(valid).to eq(true)
+        valid = DiscourseTagging.tag_topic_by_names(topic, Guardian.new(user), [tag1.name, tag2.name])
+        expect(valid).to eq(true)
+        valid = DiscourseTagging.tag_topic_by_names(topic, Guardian.new(user), [tag2.name, tag3.name])
+        expect(valid).to eq(true)
+      end
+
+      it "lets staff ignore the restriction" do
+        valid = DiscourseTagging.tag_topic_by_names(topic, Guardian.new(admin), [])
+        expect(valid).to eq(true)
+        valid = DiscourseTagging.tag_topic_by_names(topic, Guardian.new(admin), [tag3.name])
+        expect(valid).to eq(true)
+      end
+    end
   end
 
   describe '#tags_for_saving' do

spec/components/post_revisor_spec.rb

@@ -810,6 +810,37 @@ describe PostRevisor do
             end
           end
 
+          context "required tag group" do
+            fab!(:tag1) { Fabricate(:tag) }
+            fab!(:tag2) { Fabricate(:tag) }
+            fab!(:tag3) { Fabricate(:tag) }
+            fab!(:tag_group) { Fabricate(:tag_group, tags: [tag1, tag2]) }
+            fab!(:category) { Fabricate(:category, name: "beta", required_tag_group: tag_group, min_tags_from_required_group: 1) }
+
+            before do
+              post.topic.update(category: category)
+            end
+
+            it "doesn't allow removing all tags from the group" do
+              post.topic.tags = [tag1, tag2]
+              result = subject.revise!(user, raw: "lets totally update the body", tags: [])
+              expect(result).to eq(false)
+            end
+
+            it "allows removing some tags" do
+              post.topic.tags = [tag1, tag2, tag3]
+              result = subject.revise!(user, raw: "lets totally update the body", tags: [tag1.name])
+              expect(result).to eq(true)
+              expect(post.reload.topic.tags.map(&:name)).to eq([tag1.name])
+            end
+
+            it "allows admins to remove the tags" do
+              post.topic.tags = [tag1, tag2, tag3]
+              result = subject.revise!(admin, raw: "lets totally update the body", tags: [])
+              expect(result).to eq(true)
+              expect(post.reload.topic.tags.size).to eq(0)
+            end
+          end
         end
 
         context "cannot create tags" do

spec/components/topic_creator_spec.rb

@@ -126,6 +126,35 @@ describe TopicCreator do
           expect(topic).to be_valid
         end
       end
+
+      context 'required tag group' do
+        fab!(:tag_group) { Fabricate(:tag_group, tags: [tag1]) }
+        fab!(:category) { Fabricate(:category, name: "beta", required_tag_group: tag_group, min_tags_from_required_group: 1) }
+
+        it "when no tags are not present" do
+          expect do
+            TopicCreator.create(user, Guardian.new(user), valid_attrs.merge(category: category.id))
+          end.to raise_error(ActiveRecord::Rollback)
+        end
+
+        it "when tags are not part of the tag group" do
+          expect do
+            TopicCreator.create(user, Guardian.new(user), valid_attrs.merge(category: category.id, tags: ['nope']))
+          end.to raise_error(ActiveRecord::Rollback)
+        end
+
+        it "when requirement is met" do
+          topic = TopicCreator.create(user, Guardian.new(user), valid_attrs.merge(category: category.id, tags: [tag1.name, tag2.name]))
+          expect(topic).to be_valid
+          expect(topic.tags.length).to eq(2)
+        end
+
+        it "lets staff ignore the restriction" do
+          topic = TopicCreator.create(user, Guardian.new(admin), valid_attrs.merge(category: category.id))
+          expect(topic).to be_valid
+          expect(topic.tags.length).to eq(0)
+        end
+      end
     end
 
     context 'personal message' do

spec/requests/categories_controller_spec.rb

@@ -349,6 +349,7 @@ describe CategoriesController do
         it "updates attributes correctly" do
           readonly = CategoryGroup.permission_types[:readonly]
           create_post = CategoryGroup.permission_types[:create_post]
+          tag_group = Fabricate(:tag_group)
 
           put "/categories/#{category.id}.json", params: {
             name: "hello",
@@ -364,7 +365,9 @@ describe CategoriesController do
               "dancing" => "frogs"
             },
             minimum_required_tags: "",
-            allow_global_tags: 'true'
+            allow_global_tags: 'true',
+            required_tag_group_name: tag_group.name,
+            min_tags_from_required_group: 2
           }
 
           expect(response.status).to eq(200)
@@ -379,6 +382,8 @@ describe CategoriesController do
           expect(category.custom_fields).to eq("dancing" => "frogs")
           expect(category.minimum_required_tags).to eq(0)
           expect(category.allow_global_tags).to eq(true)
+          expect(category.required_tag_group_id).to eq(tag_group.id)
+          expect(category.min_tags_from_required_group).to eq(2)
         end
 
         it 'logs the changes correctly' do