Ko detection fails after app restart

herzbube / littlego

Little Go. An iOS application that lets you play the game of Go on the iPhone or iPad.

https://littlego.herzbube.ch/

Apache License 2.0

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Ko detection fails after app restart #372

Closed herzbube closed 2 years ago

herzbube commented 2 years ago

Steps to reproduce:

Start a new human vs. human game.
Create a Ko situation, e.g. play B A1, W A2, B B2, W pass, B C1, W B1 (killing black stone at A1).
Try to play B A1. The game prevents you from playing B A1 because this is a ko move.
Suspend the app, then kill the app.
Launch the app.
Try to play B A1.

Expected: The game prevents you from playing B A1 because this is a ko move. Actual: The game lets you play B A1, then reports that Fuego rejected the move.

herzbube commented 2 years ago

The problem is that Zobrist hashes are not calculated correctly when the app restores its state after a restart.

The issue was introduced by the fix for bug #357. The fix removed the archiving of GoMove properties next and previous to avoid a stack overflow error. Instead the fix introduced relinking moves after an app restart, but the relinking occurs too late, i.e. after Zobrist hash calculation.