fix bz16 - book becoming cursed while being read

Attempting to read a cursed spellbook fails with a nasty effect.  But
a non-cursed book can become cursed while being read (malignant aura
after Wizard has been killed).  Assuming no interruption for other
reasons, the read would finish, the spell be learned, and then the
nasty effect would be given.  This changes things so that if the book
being read becomes cursed and the hero notices (book's bknown flag is
set), the read-in-progress will be interrupted.  Resuming will take
the attempting-to-read-a-cursed-book path.  Unfortunately, if the
hero doesn't notice, the old behavior still applies.  Maybe the new
behavior should happen even if bknown isn't set (but then player
won't be told why the interruption occurred).

doc/fixes36.1

@@ -139,6 +139,11 @@ monsters fleeing up the upstairs on level 1 were supposed to escape the
 monster hitting fire-dealing monster with weapon triggered passive damage to
 	weapon every time, when hero doing so only had 1/6 chance per hit
 hitting steam vortex with flammable weapon would damage the weapon with fire
+if a non-cursed spellbook being read becomes cursed and hero recognizes that
+	(bknown is set), interrupt reading
+if a non-cursed spellbook being read becomes cursed and hero doesn't notice,
+	don't leave it flagged as in-use (hence to be deleted during the
+	next save/restore cycle) if contact-poison cursed book effect occurs
 
 
 Platform- and/or Interface-Specific Fixes

include/extern.h

@@ -2197,6 +2197,7 @@ E boolean FDECL(load_special, (const char *));
 
 /* ### spell.c ### */
 
+E void FDECL(book_cursed, (struct obj *));
 #ifdef USE_TRAMPOLI
 E int NDECL(learn);
 #endif

src/mkobj.c

@@ -1247,12 +1247,14 @@ void
 curse(otmp)
 register struct obj *otmp;
 {
+    unsigned already_cursed;
     int old_light = 0;
 
     if (otmp->oclass == COIN_CLASS)
         return;
     if (otmp->lamplit)
         old_light = arti_light_radius(otmp);
+    already_cursed = otmp->cursed;
     otmp->blessed = 0;
     otmp->cursed = 1;
     /* welded two-handed weapon interferes with some armor removal */
@@ -1263,14 +1265,18 @@ register struct obj *otmp;
     if (otmp == uswapwep && u.twoweap)
         drop_uswapwep();
     /* some cursed items need immediate updating */
-    if (carried(otmp) && confers_luck(otmp))
+    if (carried(otmp) && confers_luck(otmp)) {
         set_moreluck();
-    else if (otmp->otyp == BAG_OF_HOLDING)
+    } else if (otmp->otyp == BAG_OF_HOLDING) {
         otmp->owt = weight(otmp);
-    else if (otmp->otyp == FIGURINE) {
+    } else if (otmp->otyp == FIGURINE) {
         if (otmp->corpsenm != NON_PM && !dead_species(otmp->corpsenm, TRUE)
             && (carried(otmp) || mcarried(otmp)))
             attach_fig_transform_timeout(otmp);
+    } else if (otmp->oclass == SPBOOK_CLASS) {
+        /* if book hero is reading becomes cursed, interrupt */
+        if (!already_cursed)
+            book_cursed(otmp);
     }
     if (otmp->lamplit)
         maybe_adjust_light(otmp, old_light);

src/spell.c

@@ -120,6 +120,7 @@ STATIC_OVL boolean
 cursed_book(bp)
 struct obj *bp;
 {
+    boolean was_in_use;
     int lev = objects[bp->otyp].oc_level;
     int dmg = 0;
 
@@ -149,11 +150,12 @@ struct obj *bp;
             break;
         }
         /* temp disable in_use; death should not destroy the book */
+        was_in_use = bp->in_use;
         bp->in_use = FALSE;
         losestr(Poison_resistance ? rn1(2, 1) : rn1(4, 3));
         losehp(rnd(Poison_resistance ? 6 : 10), "contact-poisoned spellbook",
                KILLED_BY_AN);
-        bp->in_use = TRUE;
+        bp->in_use = was_in_use;
         break;
     case 6:
         if (Antimagic) {
@@ -322,6 +324,17 @@ struct obj *book2;
     return;
 }
 
+/* 'book' has just become cursed; if we're reading it and realize it is
+   now cursed, interrupt */
+void
+book_cursed(book)
+struct obj *book;
+{
+    if (occupation == learn && context.spbook.book == book
+        && book->cursed && book->bknown && multi >= 0)
+        stop_occupation();
+}
+
 STATIC_PTR int
 learn(VOID_ARGS)
 {
@@ -344,9 +357,8 @@ learn(VOID_ARGS)
         context.spbook.delay = 0;
         return 0;
     }
-    if (context
-            .spbook.delay) { /* not if (context.spbook.delay++), so at end
-                                delay == 0 */
+    if (context.spbook.delay) {
+        /* not if (context.spbook.delay++), so at end delay == 0 */
         context.spbook.delay++;
         return 1; /* still busy */
     }
@@ -516,15 +528,16 @@ register struct obj *spellbook;
                 too_hard = TRUE;
             } else {
                 /* uncursed - chance to fail */
-                int read_ability =
-                    ACURR(A_INT) + 4 + u.ulevel / 2
-                    - 2 * objects[booktype].oc_level
-                    + ((ublindf && ublindf->otyp == LENSES) ? 2 : 0);
+                int read_ability = ACURR(A_INT) + 4 + u.ulevel / 2
+                                   - 2 * objects[booktype].oc_level
+                             + ((ublindf && ublindf->otyp == LENSES) ? 2 : 0);
+
                 /* only wizards know if a spell is too difficult */
                 if (Role_if(PM_WIZARD) && read_ability < 20 && !confused) {
                     char qbuf[QBUFSZ];
+
                     Sprintf(qbuf,
-                     "This spellbook is %sdifficult to comprehend. Continue?",
+                    "This spellbook is %sdifficult to comprehend.  Continue?",
                             (read_ability < 12 ? "very " : ""));
                     if (yn(qbuf) != 'y') {
                         spellbook->in_use = FALSE;