Some monsters can eat through iron bars

Any monster with rusting or corrosion attack can eat through
the bars. This includes rust monsters, grey oozes, and black puddings.

Original patch by Malcolm Ryan

doc/fixes35.0

@@ -899,6 +899,7 @@ pudding corpses behave somewhat differently than before
 mithril armor should have silver color
 lichen corpse is an acid indicator
 camera may contain a picture-painting demon
+some monsters can eat through iron bars
 
 
 Platform- and/or Interface-Specific Fixes

include/extern.h

@@ -1367,6 +1367,7 @@ E boolean FDECL(onscary, (int,int,struct monst *));
 E void FDECL(monflee, (struct monst *, int, BOOLEAN_P, BOOLEAN_P));
 E int FDECL(dochug, (struct monst *));
 E int FDECL(m_move, (struct monst *,int));
+E void FDECL(dissolve_bars, (int,int));
 E boolean FDECL(closed_door, (int,int));
 E boolean FDECL(accessible, (int,int));
 E void FDECL(set_apparxy, (struct monst *));

src/hack.c

@@ -347,7 +347,7 @@ still_chewing(x,y)
 
     if (!boulder && IS_ROCK(lev->typ) && !may_dig(x,y)) {
     You("hurt your teeth on the %s.",
-        IS_TREE(lev->typ) ? "tree" : "hard stone");
+        lev->typ == IRONBARS ? "bars" : (IS_TREE(lev->typ) ? "tree" : "hard stone"));
     nomul(0);
     return 1;
     } else if (context.digging.pos.x != x || context.digging.pos.y != y ||
@@ -362,9 +362,10 @@ still_chewing(x,y)
     context.digging.effort =
         (IS_ROCK(lev->typ) && !IS_TREE(lev->typ) ? 30 : 60) + u.udaminc;
     You("start chewing %s %s.",
-        (boulder || IS_TREE(lev->typ)) ? "on a" : "a hole in the",
+        (boulder || IS_TREE(lev->typ) || lev->typ == IRONBARS) ? "on a" : "a hole in the",
         boulder ? "boulder" :
-        IS_TREE(lev->typ) ? "tree" : IS_ROCK(lev->typ) ? "rock" : "door");
+        IS_TREE(lev->typ) ? "tree" : IS_ROCK(lev->typ) ? "rock" :
+	lev->typ == IRONBARS ? "bar" : "door");
     watch_dig((struct monst *)0, x, y, FALSE);
     return 1;
     } else if ((context.digging.effort += (30 + u.udaminc)) <= 100)  {
@@ -373,7 +374,8 @@ still_chewing(x,y)
         context.digging.chew ? "continue" : "begin",
         boulder ? "boulder" :
         IS_TREE(lev->typ) ? "tree" :
-        IS_ROCK(lev->typ) ? "rock" : "door");
+        IS_ROCK(lev->typ) ? "rock" :
+	    lev->typ == IRONBARS ? "bars" : "door");
     context.digging.chew = TRUE;
     watch_dig((struct monst *)0, x, y, FALSE);
     return 1;
@@ -418,6 +420,9 @@ still_chewing(x,y)
     } else if (IS_TREE(lev->typ)) {
     digtxt = "chew through the tree.";
     lev->typ = ROOM;
+    } else if (lev->typ == IRONBARS) {
+	digtxt = "eat through the bars.";
+	dissolve_bars(x,y);
     } else if (lev->typ == SDOOR) {
     if (lev->doormask & D_TRAPPED) {
         lev->doormask = D_NODOOR;
@@ -630,10 +635,15 @@ int mode;
     if (Passes_walls && may_passwall(x,y)) {
         ;	/* do nothing */
     } else if (tmpr->typ == IRONBARS) {
+	    if ((dmgtype(youmonst.data, AD_RUST) ||
+		 dmgtype(youmonst.data, AD_CORR)) &&
+		mode == DO_MOVE && still_chewing(x,y)) {
+		return FALSE;
+	    }
 	    if (!(Passes_walls || passes_bars(youmonst.data))) {
 		if (iflags.mention_walls)
 		    You("cannot pass through the bars.");
-        return FALSE;
+		return FALSE;
 	    }
     } else if (tunnels(youmonst.data) && !needspick(youmonst.data)) {
         /* Eat the rock. */

src/mondata.c

@@ -285,6 +285,7 @@ struct permonst *mptr;
 {
     return (boolean) (passes_walls(mptr) || amorphous(mptr) ||
 		      unsolid(mptr) || is_whirly(mptr) || verysmall(mptr) ||
+		      dmgtype(mptr, AD_CORR) || dmgtype(mptr, AD_RUST) ||
 		      (slithy(mptr) && !bigmonst(mptr)));
 }
 

src/monmove.c

@@ -1180,7 +1180,14 @@ postmov:
 			    add_damage(mtmp->mx, mtmp->my, 0L);
 		    }
 		} else if (levl[mtmp->mx][mtmp->my].typ == IRONBARS) {
-			if (flags.verbose && canseemon(mtmp))
+		    if (may_dig(mtmp->mx,mtmp->my) &&
+			(dmgtype(ptr, AD_RUST) || dmgtype(ptr, AD_CORR))) {
+			if (canseemon(mtmp))
+			    pline("%s eats through the iron bars.",
+				  Monnam(mtmp));
+			dissolve_bars(mtmp->mx, mtmp->my);
+			return(3);
+		    } else if (flags.verbose && canseemon(mtmp))
 			    Norep("%s %s %s the iron bars.", Monnam(mtmp),
 				  /* pluralization fakes verb conjugation */
 				  makeplural(locomotion(ptr, "pass")),
@@ -1266,6 +1273,14 @@ postmov:
 	return(mmoved);
 }
 
+void
+dissolve_bars(x, y)
+register int x, y;
+{
+    levl[x][y].typ = (Is_special(&u.uz) || *in_rooms(x,y,0)) ? ROOM : CORR;
+    newsym(x, y);
+}
+
 boolean
 closed_door(x, y)
 register int x, y;