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Similarly to the previous commit, if you started Pearl with at least some kinds of invalid puzzle (e.g. "6x6:abBfWcWWrBa") and then pressed 'h' to get hints, you could provoke an assertion failure. But this time the assertion wasn't in the solver itself; the solver gave up gracefully and didn't crash, but it _did_ leave the links between squares in the game_state in an inconsistent state, in that one square was marked as linking to its neighbour without the neighbour also linking back to it. This caused the /* should have reciprocal link */ assertion in dsf_update_completion to fail, when that was called from check_completion after the solver had finished, to decide whether the puzzle was now solved. In this commit, I arrange that whether or not pearl_solve returns a grid layout that's legal by the rules of the _puzzle_, it at least returns one that's legal by the rules of the _data representation_, in that every link between squares is either bidirectional or absent. This is a better solution than just removing the assertion, because if the inconsistent data were allowed to persist, it would lead to further problems in gameplay. For example, if you just remove that assertion instead of this fix and press 'h' on the example puzzle id above, you'll find that the non-reciprocal links are actually visible, in the form of several thick lines that stop at a grid square boundary instead of connecting two square-centres. (It looks even sillier if you set PEARL_GUI_LOOPY=y.) That's a situation that can't be created by a normal move, and if you try to make normal moves after it (e.g. click one of the weird edges), you'll find that both sides of the half-link get toggled, so now it's a half-link the other way round. So not only can't you _create_ this situation in normal play, you can't get rid of it either! That assertion in dsf_update_completion was commented out at one point, and I put it back in commit c5500926bf7458a saying that if it failed I'd like to know about it. And indeed, I'm glad I did, because this kind of unfixable wrongness in the resulting game_state was worth noticing and getting rid of!
This is the README accompanying the source code to Simon Tatham's puzzle collection. The collection's web site is at <https://www.chiark.greenend.org.uk/~sgtatham/puzzles/>. The puzzle collection is built using CMake <https://cmake.org/>. To compile in the simplest way (on any of Linux, Windows or Mac), run these commands in the source directory: cmake . cmake --build . The manual is provided in Windows Help format for the Windows build; in text format for anyone who needs it; and in HTML for the Mac OS X application and for the web site. It is generated from a Halibut source file (puzzles.but), which is the preferred form for modification. To generate the manual in other formats, rebuild it, or learn about Halibut, visit the Halibut website at <https://www.chiark.greenend.org.uk/~sgtatham/halibut/>.