I found a slightly odd-looking line of code in this file a few days

[sgt/puzzles] / midend.c

diff --git a/midend.c b/midend.c
index 64edfd3..833cbef 100644 (file)
--- a/midend.c
+++ b/midend.c
@@ -356,8 +356,24 @@ void midend_new_game(midend *me)
     }
 
     ensure(me);
+
+    /*
+     * It might seem a bit odd that we're using me->params to
+     * create the initial game state, rather than me->curparams
+     * which is better tailored to this specific game and which we
+     * always know.
+     * 
+     * It's supposed to be an invariant in the midend that
+     * me->params and me->curparams differ in no aspect that is
+     * important after generation (i.e. after new_desc()). By
+     * deliberately passing the _less_ specific of these two
+     * parameter sets, we provoke play-time misbehaviour in the
+     * case where a game has failed to encode a play-time parameter
+     * in the non-full version of encode_params().
+     */
     me->states[me->nstates].state =
        me->ourgame->new_game(me, me->params, me->desc);
+
     me->states[me->nstates].movestr = NULL;
     me->states[me->nstates].movetype = NEWGAME;
     me->nstates++;
@@ -1167,12 +1183,15 @@ char *midend_solve(midend *me)
     if (me->statepos < 1)
        return "No game set up to solve";   /* _shouldn't_ happen! */
 
-    msg = "Solve operation failed";    /* game _should_ overwrite on error */
+    msg = NULL;
     movestr = me->ourgame->solve(me->states[0].state,
                                 me->states[me->statepos-1].state,
                                 me->aux_info, &msg);
-    if (!movestr)
+    if (!movestr) {
+       if (!msg)
+           msg = "Solve operation failed";   /* _shouldn't_ happen, but can */
        return msg;
+    }
     s = me->ourgame->execute_move(me->states[me->statepos-1].state, movestr);
     assert(s);