FEATURE: align with /filter and allow multiple category search (#27440)

This introduces the syntax of

`category:a,b,c` which will search across multiple categories.

Previously there was no way to allow search across a wide selection of
categories.

lib/search.rb

@@ -542,20 +542,46 @@ class Search
 
   advanced_filter(/\Awith:images\z/i) { |posts| posts.where("posts.image_upload_id IS NOT NULL") }
 
-  advanced_filter(/\Acategory:(.+)\z/i) do |posts, match|
-    exact = false
+  advanced_filter(/\Acategor(?:y|ies):(.+)\z/i) do |posts, terms|
+    category_ids = []
 
-    if match[0] == "="
-      exact = true
-      match = match[1..-1]
+    matches =
+      terms
+        .split(",")
+        .map do |term|
+          if term[0] == "="
+            [term[1..-1], true]
+          else
+            [term, false]
+          end
+        end
+        .to_h
+
+    if matches.present?
+      sql = <<~SQL
+      SELECT c.id, term
+      FROM
+          categories c
+      JOIN
+          unnest(ARRAY[:matches]) AS term ON
+          c.slug ILIKE term OR
+          c.name ILIKE term OR
+          (term ~ '^[0-9]{1,10}$' AND c.id = term::int)
+      SQL
+
+      found = DB.query(sql, matches: matches.keys)
+
+      if found.present?
+        found.each do |row|
+          category_ids << row.id
+          @category_filter_matched ||= true
+          category_ids += Category.subcategory_ids(row.id) if !matches[row.term]
+        end
+      end
     end
 
-    category_ids =
-      Category.where("slug ilike ? OR name ilike ? OR id = ?", match, match, match.to_i).pluck(:id)
     if category_ids.present?
-      category_ids += Category.subcategory_ids(category_ids.first) unless exact
-      @category_filter_matched ||= true
-      posts.where("topics.category_id IN (?)", category_ids)
+      posts.where("topics.category_id IN (?)", category_ids.uniq)
     else
       posts.where("1 = 0")
     end

spec/lib/search_spec.rb

@@ -1255,6 +1255,41 @@ RSpec.describe Search do
       )
     end
 
+    it "allow searching for multiple categories" do
+      category2 = Fabricate(:category, name: "abc")
+      topic2 = Fabricate(:topic, category: category2)
+      post2 = Fabricate(:post, topic: topic2, raw: "snow monkey")
+
+      category3 = Fabricate(:category, name: "def")
+      topic3 = Fabricate(:topic, category: category3)
+      post3 = Fabricate(:post, topic: topic3, raw: "snow monkey")
+
+      search = Search.execute("monkey category:abc,def")
+      expect(search.posts.map(&:id)).to contain_exactly(post2.id, post3.id)
+
+      search = Search.execute("monkey categories:abc,def")
+      expect(search.posts.map(&:id)).to contain_exactly(post2.id, post3.id)
+
+      search = Search.execute("monkey categories:xxxxx,=abc,=def")
+      expect(search.posts.map(&:id)).to contain_exactly(post2.id, post3.id)
+
+      search = Search.execute("snow category:abc,#{category.id}")
+      expect(search.posts.map(&:id)).to contain_exactly(post.id, post2.id)
+
+      child_category = Fabricate(:category, parent_category: category2)
+      child_topic = Fabricate(:topic, category: child_category)
+      child_post = Fabricate(:post, topic: child_topic, raw: "snow monkey")
+
+      search = Search.execute("monkey category:zzz,nnn,=abc,mmm")
+      expect(search.posts.map(&:id)).to contain_exactly(post2.id)
+
+      search =
+        Search.execute(
+          "monkey category:0007847874874874874748749398384398439843984938439843948394834984934839483984983498394834983498349834983,zzz,nnn,abc,mmm",
+        )
+      expect(search.posts.map(&:id)).to contain_exactly(post2.id, child_post.id)
+    end
+
     it "should return the right categories" do
       search = Search.execute("monkey")