Search for operator words instead of parsing them

The search box keeps only word characters, but FTS5 still reads AND, OR,
NOT and NEAR in the query as operators, so searching for "AND" or for
"salt AND" raised "fts5: syntax error" and answered with a 500. Quoting
each word makes FTS5 look for it as text, which is how it already treats
the same words in lower case.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NuTtwJKhb77Dv7EQqv2C3C

app/models/message/searchable.rb

@@ -6,7 +6,15 @@ module Message::Searchable
     after_update_commit  :update_in_index
     after_destroy_commit :remove_from_index
 
-    scope :search, ->(query) { joins("join message_search_index idx on messages.id = idx.rowid").where("idx.body match ?", query).ordered }
+    scope :search, ->(query) { joins("join message_search_index idx on messages.id = idx.rowid").where("idx.body match ?", match_terms(query)).ordered }
+  end
+
+  class_methods do
+    # Quotes each word, so that FTS5 searches for AND, OR, NOT and NEAR rather than
+    # parsing them as operators, which fails on a query like "AND" or "salt AND".
+    def match_terms(query)
+      query.split.map { |word| %("#{word.gsub('"', '""')}") }.join(" ")
+    end
   end
 
   private

test/controllers/searches_controller_test.rb

@@ -20,6 +20,24 @@ class SearchesControllerTest < ActionDispatch::IntegrationTest
     assert_select ".message", text: /Hello world!/
   end
 
+  test "operator words are searched for as words" do
+    rooms(:designers).messages.create! body: "Salt and pepper", client_message_id: "operators", creator: users(:david)
+
+    get searches_url, params: { q: "salt AND" }
+
+    assert_response :success
+    assert_select ".message", text: /Salt and pepper/
+  end
+
+  test "searching for an operator word alone doesn't fail" do
+    %w[ AND OR NOT ].each do |word|
+      get searches_url, params: { q: word }
+
+      assert_response :success
+      assert_select ".message", count: 0
+    end
+  end
+
   test "unreachable messages are not found" do
     memberships(:david_designers).destroy!
 

test/models/message_test.rb

@@ -65,6 +65,12 @@ class MessageTest < ActiveSupport::TestCase
     assert_equal room.messages.ordered.first(Message::Pagination::PAGE_SIZE).map(&:id), room.messages.first_page.map(&:id)
   end
 
+  test "search reads quotes and operator words in the query as text" do
+    message = rooms(:designers).messages.create!(body: "Say hi, NOT bye", client_message_id: "quoted", creator: users(:david))
+
+    assert_equal [ message ], Message.search(%(say "hi NOT)).to_a
+  end
+
   private
     def create_new_message_in(room)
       room.messages.create!(creator: users(:jason), body: "Hello", client_message_id: "123")