fix issue #1350 - shop purchasing

Aka issue #1339 take II

For hero-owned container with some unpaid items, the itemized
shopping bill had a spurious index into the traditional shopping
bill (since it wasn't in that bill due not being unpaid).  When mixed
with unpaid items that weren't in the container, that could cause
bill corruption while updating the traditional bill during payment,
leading to impossible warnings.

Fixes #1339
Fixes #1350

src/shk.c

@@ -33,11 +33,15 @@ enum billitem_status {
    unpaid and by cost within each of those two categories */
 struct sortbill_item {
     struct obj *obj;
-    long cost;
-    long quan;
-    int bidx;
-    int8 usedup; /* small but signed */
-    boolean queuedpay;
+    long cost;   /* full amount for current quantity, not per-unit amount */
+    long quan;   /* count for this entry; subset if this is partly used or
+                  * partly intact */
+    int bidx;    /* index into ESHK(shkp)->bill_p[]; hero-owned container,
+                  * which isn't in bill_p[], uses bidx == -1 */
+    int8 usedup; /* billitem_status, small but needs to be signed for qsort()
+                  * [for an earlier edition; 'signed' no longer necessary] */
+    boolean queuedpay; /* buy without asking when containers are involved
+                        * or purchase targets have been picked via menu */
 };
 typedef struct sortbill_item Bill;
 
@@ -1457,6 +1461,7 @@ cheapest_item(int ibillct, Bill *ibill)
     return gmin;
 }
 
+
 /* for itemized purchasing, create an alternate shop bill that hides
    container contents */
 staticfn int /* returns number of entries */
@@ -1469,7 +1474,7 @@ make_itemized_bill(
     struct bill_x *bp;
     struct obj *otmp;
     struct eshk *eshkp = ESHK(shkp);
-    int i, n, ebillct = eshkp->billct;
+    int i, n, bidx, ebillct = eshkp->billct;
     int8 used;
     long quan, cost;
 
@@ -1491,6 +1496,7 @@ make_itemized_bill(
             impossible("Can't find shop bill entry for #%d", bp->bo_id);
             continue;
         }
+        bidx = i; /* index into bill_p[], except for hero-owner container */
 
         if (otmp->quan == 0L || otmp->where == OBJ_ONBILL) {
             /* item is completely used up; restore quantity from when it
@@ -1506,7 +1512,7 @@ make_itemized_bill(
             ibill[n].obj = otmp;
             ibill[n].quan = bp->bquan - otmp->quan;
             ibill[n].cost = bp->price * ibill[n].quan;
-            ibill[n].bidx = i; /* duplicate index into eshkp->bill_p[] */
+            ibill[n].bidx = bidx; /* duplicate index into eshkp->bill_p[] */
             ibill[n].usedup = PartlyUsedUp; /* for sorting */
             ++n; /* intact portion will be a separate entry, next */
         }
@@ -1547,6 +1553,8 @@ make_itemized_bill(
             /* include 1 container containing unpaid item(s) */
             quan = 1L;
             cost = unpaid_cost(otmp, COST_CONTENTS);
+            if (!otmp->unpaid)
+                bidx = -1;
             /* an unpaid container without any unpaid contents is classified
                as 'FullyIntact'; a container with unpaid contents will be
                '*Container' regardless of whether it is unpaid itself */
@@ -1564,7 +1572,7 @@ make_itemized_bill(
         ibill[n].obj = otmp;
         ibill[n].quan = quan;
         ibill[n].cost = cost;
-        ibill[n].bidx = i;
+        ibill[n].bidx = bidx;
         ibill[n].usedup = used;
         ++n;
     }
@@ -2034,11 +2042,7 @@ pay_billed_items(
         if (queuedpay && !ibill[indx].queuedpay)
             continue;
 
-        bidx = ibill[indx].bidx;
-        bp = &eshkp->bill_p[bidx];
-        otmp = ibill[indx].obj;
-        pass = (ibill[indx].usedup <= PartlyUsedUp) ? 0 : 1;
-
+        otmp = ibill[indx].obj; /* ordinary object or outermost container */
         if (ibill[indx].usedup >= KnownContainer) {
             /* when successfull, buy_container() will call both
                dopayobj() and update_bill(), possibly multiple times */
@@ -2054,6 +2058,10 @@ pay_billed_items(
                 buy = PAY_CANT;
             }
         } else {
+            bidx = ibill[indx].bidx;
+            bp = &eshkp->bill_p[bidx];
+            pass = (ibill[indx].usedup <= PartlyUsedUp) ? 0 : 1;
+
             buy = dopayobj(shkp, bp, otmp, pass, itemize, FALSE);
 
             if (buy == PAY_BUY)
@@ -2091,12 +2099,11 @@ update_bill(
     struct obj *paiditem)
 {
     int j, newebillct;
-    int bidx = ibill[indx].bidx;
 
     /* remove from eshkp->bill_p[] unless this was the used up portion
        of partly used item (since removal would take out both; note:
        can't buy PartlyIntact until PartlyUsedUp has been paid for) */
-    if (ibill[indx].usedup == PartlyUsedUp) {
+    if (indx >= 0 && ibill[indx].usedup == PartlyUsedUp) {
         /* 'paiditem' points to the partly intact portion still in invent or
            inside a container (ibill[indx].obj points to the container) */
         bp->bquan = paiditem->quan;
@@ -2117,13 +2124,11 @@ update_bill(
         }
         newebillct = eshkp->billct - 1;
         *bp = eshkp->bill_p[newebillct];
-#if 0   /* [this is responsible for github issue #1339; it's not clear why] */
-        for (j = 0; j < ibillct; ++j)
-            if (ibill[j].bidx == newebillct)
-                ibill[j].bidx = bidx;
-#else
-        nhUse(bidx);
-#endif
+        if (indx >= 0) {
+            for (j = 0; j < ibillct; ++j)
+                if (ibill[j].bidx == newebillct)
+                    ibill[j].bidx = ibill[indx].bidx;
+        }
         eshkp->billct = newebillct; /* eshkp->billct - 1 */
     }
     return;
@@ -2306,7 +2311,7 @@ buy_container(
         }
         /* [updating cost here is not necessary but useful when debugging] */
         ibill[indx].cost -= (bp->price * bp->bquan); /* update container */
-        update_bill(indx, ibillct, ibill, eshkp, bp, otmp);
+        update_bill(-1, ibillct, ibill, eshkp, bp, otmp);
         ++buycount;
     }
     if (buycount && sightunseen) {