DEV: Support filter for topics in specific subcategories on /filter (#20927)

This commit adds support for filtering for topics in specific
subcategories via the categories filter query language.

For example: `category:documentation:admins` will filter for topics and
subcategory topics in
the category with slug "admins" whose parent category has the slug
"documentation".

The `=` prefix can also be used such that
`=category:documentation:admins` will exclude subcategory topics of the
category with slug "admins" whose parent category has the slug
"documentation".

app/models/category.rb

@@ -215,6 +215,48 @@ class Category < ActiveRecord::Base
     Category.reset_topic_ids_cache
   end
 
+  # Accepts an array of slugs with each item in the array
+  # Returns the category ids of the last slug in the array. The slugs array has to follow the proper category
+  # nesting hierarchy. If any of the slug in the array is invalid or if the slugs array does not follow the proper
+  # category nesting hierarchy, nil is returned.
+  #
+  # When only a single slug is provided, the category id of all the categories with that slug is returned.
+  def self.ids_from_slugs(slugs)
+    return [] if slugs.blank?
+
+    params = {}
+    params_index = 0
+
+    sqls =
+      slugs.map do |slug|
+        category_slugs = slug.split(":").first(SiteSetting.max_category_nesting)
+        sql = ""
+
+        if category_slugs.length == 1
+          params[:"slug_#{params_index}"] = category_slugs.first
+          sql = "SELECT id FROM categories WHERE slug = :slug_#{params_index}"
+          params_index += 1
+        else
+          category_slugs.each_with_index do |category_slug, index|
+            params[:"slug_#{params_index}"] = category_slug
+
+            sql =
+              if index == 0
+                "SELECT id FROM categories WHERE slug = :slug_#{params_index} AND parent_category_id IS NULL"
+              else
+                "SELECT id FROM categories WHERE parent_category_id = (#{sql}) AND slug = :slug_#{params_index}"
+              end
+
+            params_index += 1
+          end
+        end
+
+        sql
+      end
+
+    DB.query_single(sqls.join("\nUNION ALL\n"), params)
+  end
+
   @@subcategory_ids = DistributedCache.new("subcategory_ids")
 
   def self.subcategory_ids(category_id)

lib/topics_filter.rb

@@ -10,7 +10,7 @@ class TopicsFilter
     return @scope if query_string.blank?
 
     query_string.scan(
-      /(?<key_prefix>[-=])?(?<key>\w+):(?<value>[^:\s]+)/,
+      /(?<key_prefix>[-=])?(?<key>\w+):(?<value>[^\s]+)/,
     ) do |key_prefix, key, value|
       case key
       when "status"
@@ -37,7 +37,7 @@ class TopicsFilter
         end
       when "category", "categories"
         value.scan(
-          /^(?<category_slugs>([a-zA-Z0-9\-]+)(?<delimiter>[,])?([a-zA-Z0-9\-]+)?(\k<delimiter>[a-zA-Z0-9\-]+)*)$/,
+          /^(?<category_slugs>([a-zA-Z0-9\-:]+)(?<delimiter>[,])?([a-zA-Z0-9\-:]+)?(\k<delimiter>[a-zA-Z0-9\-:]+)*)$/,
         ) do |category_slugs, delimiter|
           break if key_prefix && key_prefix != "="
 
@@ -81,13 +81,16 @@ class TopicsFilter
   private
 
   def filter_categories(category_slugs:, exclude_subcategories: false)
+    category_ids = Category.ids_from_slugs(category_slugs)
+
     category_ids =
       Category
-        .where(slug: category_slugs)
+        .where(id: category_ids)
         .filter { |category| @guardian.can_see_category?(category) }
         .map(&:id)
 
-    return @scope.none if category_ids.length != category_slugs.length
+    # Don't return any records if the user does not have access to any of the categories
+    return @scope.none if category_ids.length < category_slugs.length
 
     if !exclude_subcategories
       category_ids = category_ids.flat_map { |category_id| Category.subcategory_ids(category_id) }

spec/lib/topics_filter_spec.rb

@@ -159,6 +159,152 @@ RSpec.describe TopicsFilter do
           ).to contain_exactly(topic_in_category.id, topic_in_category2.id)
         end
       end
+
+      describe "when multiple categories have subcategories with the same name" do
+        fab!(:category_subcategory) do
+          Fabricate(:category, parent_category: category, name: "subcategory")
+        end
+
+        fab!(:category2_subcategory) do
+          Fabricate(:category, parent_category: category2, name: "subcategory")
+        end
+
+        fab!(:topic_in_category_subcategory) { Fabricate(:topic, category: category_subcategory) }
+        fab!(:topic_in_category2_subcategory) { Fabricate(:topic, category: category2_subcategory) }
+
+        describe "when query string is `category:subcategory`" do
+          it "should return topics from subcategories of both categories" do
+            expect(
+              TopicsFilter
+                .new(guardian: Guardian.new)
+                .filter_from_query_string("category:subcategory")
+                .pluck(:id),
+            ).to contain_exactly(
+              topic_in_category_subcategory.id,
+              topic_in_category2_subcategory.id,
+            )
+          end
+        end
+
+        describe "when query string is `category:category:subcategory`" do
+          it "should return topics from subcategories of the specified category" do
+            expect(
+              TopicsFilter
+                .new(guardian: Guardian.new)
+                .filter_from_query_string("category:category:subcategory")
+                .pluck(:id),
+            ).to contain_exactly(topic_in_category_subcategory.id)
+          end
+        end
+
+        describe "when query string is `category:category2:subcategory`" do
+          it "should return topics from subcategories of the specified category" do
+            expect(
+              TopicsFilter
+                .new(guardian: Guardian.new)
+                .filter_from_query_string("category:category2:subcategory")
+                .pluck(:id),
+            ).to contain_exactly(topic_in_category2_subcategory.id)
+          end
+        end
+
+        describe "when query string is `category:category:subcategory,category2:subcategory`" do
+          it "should return topics from either subcategory" do
+            expect(
+              TopicsFilter
+                .new(guardian: Guardian.new)
+                .filter_from_query_string("category:category:subcategory,category2:subcategory")
+                .pluck(:id),
+            ).to contain_exactly(
+              topic_in_category_subcategory.id,
+              topic_in_category2_subcategory.id,
+            )
+          end
+        end
+
+        describe "when max category nesting is 3" do
+          fab!(:category_subcategory_subcategory) do
+            SiteSetting.max_category_nesting = 3
+            Fabricate(:category, parent_category: category_subcategory, name: "sub-subcategory")
+          end
+
+          fab!(:category2_subcategory_subcategory) do
+            SiteSetting.max_category_nesting = 3
+            Fabricate(:category, parent_category: category2_subcategory, name: "sub-subcategory")
+          end
+
+          fab!(:topic_in_category_subcategory_subcategory) do
+            Fabricate(:topic, category: category_subcategory_subcategory)
+          end
+
+          fab!(:topic_in_category2_subcategory_subcategory) do
+            Fabricate(:topic, category: category2_subcategory_subcategory)
+          end
+
+          before { SiteSetting.max_category_nesting = 3 }
+
+          describe "when query string is `category:category:subcategory:sub-subcategory`" do
+            it "return topics from category with slug 'sub-subcategory' with the category ancestor chain of 'subcategory' and 'category'" do
+              expect(
+                TopicsFilter
+                  .new(guardian: Guardian.new)
+                  .filter_from_query_string("category:category:subcategory:sub-subcategory")
+                  .pluck(:id),
+              ).to contain_exactly(topic_in_category_subcategory_subcategory.id)
+            end
+          end
+
+          describe "when query string is `=category:category2:subcategory`" do
+            it "return topics from category with slug 'subcategory' with the category ancestor chain of 'category2'" do
+              expect(
+                TopicsFilter
+                  .new(guardian: Guardian.new)
+                  .filter_from_query_string("=category:category2:subcategory")
+                  .pluck(:id),
+              ).to contain_exactly(topic_in_category2_subcategory.id)
+            end
+          end
+
+          describe "when query string is `category:category2:subcategory`" do
+            it "return topics and subcategories topics from category with slug 'subcategory' with the category ancestor chain of 'category2'" do
+              category2_subcategory_subcategory2 =
+                Fabricate(
+                  :category,
+                  parent_category: category2_subcategory,
+                  name: "sub-subcategory2",
+                )
+
+              topic_in_category2_subcategory_subcategory2 =
+                Fabricate(:topic, category: category2_subcategory_subcategory2)
+
+              expect(
+                TopicsFilter
+                  .new(guardian: Guardian.new)
+                  .filter_from_query_string("category:category2:subcategory")
+                  .pluck(:id),
+              ).to contain_exactly(
+                topic_in_category2_subcategory.id,
+                topic_in_category2_subcategory_subcategory.id,
+                topic_in_category2_subcategory_subcategory2.id,
+              )
+            end
+          end
+
+          describe "when query string is `category:sub-subcategory`" do
+            it "return topics from either category with slug 'sub-subcategory'" do
+              expect(
+                TopicsFilter
+                  .new(guardian: Guardian.new)
+                  .filter_from_query_string("category:sub-subcategory")
+                  .pluck(:id),
+              ).to contain_exactly(
+                topic_in_category_subcategory_subcategory.id,
+                topic_in_category2_subcategory_subcategory.id,
+              )
+            end
+          end
+        end
+      end
     end
 
     describe "when filtering by status" do

spec/models/category_spec.rb

@@ -1352,4 +1352,77 @@ RSpec.describe Category do
       expect(SiteSetting.general_category_id).to be < 1
     end
   end
+
+  describe ".ids_from_slugs" do
+    fab!(:category) { Fabricate(:category, slug: "category") }
+    fab!(:category2) { Fabricate(:category, slug: "category2") }
+    fab!(:subcategory) { Fabricate(:category, parent_category: category, slug: "subcategory") }
+    fab!(:subcategory2) { Fabricate(:category, parent_category: category2, slug: "subcategory") }
+
+    it "returns [] when inputs is []" do
+      expect(Category.ids_from_slugs([])).to eq([])
+    end
+
+    it 'returns the ids of category when input is ["category"]' do
+      expect(Category.ids_from_slugs(%w[category])).to contain_exactly(category.id)
+    end
+
+    it 'returns the ids of subcategory when input is ["category:subcategory"]' do
+      expect(Category.ids_from_slugs(%w[category:subcategory])).to contain_exactly(subcategory.id)
+    end
+
+    it 'returns the ids of subcategory2 when input is ["category2:subcategory"]' do
+      expect(Category.ids_from_slugs(%w[category2:subcategory])).to contain_exactly(subcategory2.id)
+    end
+
+    it "returns the ids of category and category2 when input is ['category', 'category2']" do
+      expect(Category.ids_from_slugs(%w[category category2])).to contain_exactly(
+        category.id,
+        category2.id,
+      )
+    end
+
+    it "returns the ids of subcategory and subcategory2 when input is ['category:subcategory', 'category2:subcategory']" do
+      expect(
+        Category.ids_from_slugs(%w[category:subcategory category2:subcategory]),
+      ).to contain_exactly(subcategory.id, subcategory2.id)
+    end
+
+    it "returns the ids of subcategory when input is ['category:subcategory', 'invalid:subcategory']" do
+      expect(
+        Category.ids_from_slugs(%w[category:subcategory invalid:subcategory]),
+      ).to contain_exactly(subcategory.id)
+    end
+
+    it 'returns the ids of sub-subcategory when input is ["category:subcategory:sub-subcategory"] and maximum category nesting is 3' do
+      SiteSetting.max_category_nesting = 3
+      sub_subcategory = Fabricate(:category, parent_category: subcategory, slug: "sub-subcategory")
+
+      expect(Category.ids_from_slugs(%w[category:subcategory:sub-subcategory])).to contain_exactly(
+        sub_subcategory.id,
+      )
+    end
+
+    it 'returns nil when input is ["category:invalid-slug:sub-subcategory"] and maximum category nesting is 3' do
+      SiteSetting.max_category_nesting = 3
+      sub_subcategory = Fabricate(:category, parent_category: subcategory, slug: "sub-subcategory")
+
+      expect(Category.ids_from_slugs(%w[category:invalid-slug:sub-subcategory])).to eq([])
+    end
+
+    it 'returns the ids of subcategory when input is ["category:subcategory:sub-subcategory"] but maximum category nesting is 2' do
+      SiteSetting.max_category_nesting = 2
+
+      expect(Category.ids_from_slugs(%w[category:subcategory:sub-subcategory])).to contain_exactly(
+        subcategory.id,
+      )
+    end
+
+    it 'returns the ids of subcategory and subcategory2 when input is ["subcategory"]' do
+      expect(Category.ids_from_slugs(%w[subcategory])).to contain_exactly(
+        subcategory.id,
+        subcategory2.id,
+      )
+    end
+  end
 end