Add API parameter to safeguard unexpect mentions in new posts (#18350)

spec/services/post_status_service_spec.rb

@@ -138,7 +138,26 @@ RSpec.describe PostStatusService, type: :service do
     status = subject.call(account, text: "test status update")
 
     expect(ProcessMentionsService).to have_received(:new)
-    expect(mention_service).to have_received(:call).with(status)
+    expect(mention_service).to have_received(:call).with(status, save_records: false)
+  end
+
+  it 'safeguards mentions' do
+    account = Fabricate(:account)
+    mentioned_account = Fabricate(:account, username: 'alice')
+    unexpected_mentioned_account = Fabricate(:account, username: 'bob')
+
+    expect do
+      subject.call(account, text: '@alice hm, @bob is really annoying lately', allowed_mentions: [mentioned_account.id])
+    end.to raise_error(an_instance_of(PostStatusService::UnexpectedMentionsError).and having_attributes(accounts: [unexpected_mentioned_account]))
+  end
+
+  it 'processes duplicate mentions correctly' do
+    account = Fabricate(:account)
+    mentioned_account = Fabricate(:account, username: 'alice')
+
+    expect do
+      subject.call(account, text: '@alice @alice @alice hey @alice')
+    end.not_to raise_error
   end
 
   it 'processes hashtags' do

spec/services/process_mentions_service_spec.rb

@@ -47,6 +47,19 @@ RSpec.describe ProcessMentionsService, type: :service do
         end
       end
 
+      context 'mentioning a user several times when not saving records' do
+        let!(:remote_user) { Fabricate(:account, username: 'remote_user', protocol: :activitypub, domain: 'example.com', inbox_url: 'http://example.com/inbox') }
+        let(:status)       { Fabricate(:status, account: account, text: "Hello @#{remote_user.acct} @#{remote_user.acct} @#{remote_user.acct}", visibility: :public) }
+
+        before do
+          subject.call(status, save_records: false)
+        end
+
+        it 'creates exactly one mention' do
+          expect(status.mentions.size).to eq 1
+        end
+      end
+
       context 'with an IDN domain' do
         let!(:remote_user) { Fabricate(:account, username: 'sneak', protocol: :activitypub, domain: 'xn--hresiar-mxa.ch', inbox_url: 'http://example.com/inbox') }
         let!(:status) { Fabricate(:status, account: account, text: "Hello @sneak@hæresiar.ch") }