ref: 5030d87903191d581586ecda2382ad5bcd70f63d
parent: 517b14e666b0b71fc0bcd5da1b22cdc90d3434c9
author: Simon Tatham <anakin@pobox.com>
date: Sun Feb 5 05:29:42 EST 2023
latin_solver_alloc: handle clashing numbers in input grid. In the setup phase of the centralised latin.c solver, we start by going over the input grid containing already-placed clue numbers, and calling latin_solver_place to enter each on into the solver's data structure. This has the side effect of ruling out each number from the rest of the row and column, and _also_ checking by assertion that the number being placed is not ruled out. Those are a bad combination, because it means that if you give an obviously inconsistent input grid to latin_solver_alloc (e.g. with two identical numbers in a row already), it will fail an assertion. In that situation, you want the solver run as a whole to return diff_impossible so that the error is reported cleanly. This assertion failure could be provoked by giving either Towers or Group a manually-constructed game description inconsistent in that way, and hitting Solve. Worse, it could be provoked during live play in Unequal, by filling in a number clashing with a clue and then pressing 'h' to get hints.