fix github issue #1170 - trapped without a trap

Issue reported by mkuoppal:  drum of earthquake triggers a sanity
check warning which the fuzzer escalated to panic.

Analysis by entrez.  If a pit gets created next to a pool or moat or
lava, liquid might flow there and replace the pit.  But the drum of
earthquake code assumed that the pit was still there.  If there was a
monster there and it wasn't levitating or flying and it wasn't killed
by the liquid, it got marked as trapped even though the pit was gone.
'sanity_check' noticed.

With difficulty I was able to reproduce the impossible warning before
the fix, but the are a bunch of random factors at play.  After the
fix I can't reproduce it again, but that's not a guarantee that it's
actually fixed.  The analysis seems correct though and the fix is
based on dealing with that.

Closes #1170

doc/fixes3-7-0.txt

@@ -1323,6 +1323,11 @@ change [master] mind flayer, the Wizard, and the riders to bright magenta
 walking into a shopkeeper tries to pay the bill
 show billed items in a menu when paying with non-traditional menustyle
 prioritize paying shopkeeper next to you even if multiple are detected
+avoid impossible "trapped without a trap (fmon)" from 'sanity_check' when a
+	drum of earthquake made a pit at a monster's spot and pit creation
+	caused adjacent pool/moat/lava to flood that spot; if a non-floater,
+	non-flyer monster survived that it got marked as trapped even though
+	flooding deleted the trap
 
 
 Fixes to 3.7.0-x General Problems Exposed Via git Repository

src/dig.c

@@ -1,4 +1,4 @@
-/* NetHack 3.7	dig.c	$NHDT-Date: 1596498156 2020/08/03 23:42:36 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.142 $ */
+/* NetHack 3.7	dig.c	$NHDT-Date: 1702206282 2023/12/10 11:04:42 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.204 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Michael Allison, 2012. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -747,19 +747,32 @@ digactualhole(coordxy x, coordxy y, struct monst *madeby, int ttyp)
 DISABLE_WARNING_FORMAT_NONLITERAL
 
 /*
- * Called from dighole(), but also from do_break_wand()
- * in apply.c.
+ * Called from dighole(); also from do_break_wand() in apply.c
+ * and do_earthquake() in music.c.
  */
 void
-liquid_flow(coordxy x, coordxy y, schar typ, struct trap *ttmp,
-            const char *fillmsg)
+liquid_flow(
+    coordxy x, coordxy y,
+    schar typ,
+    struct trap *ttmp,
+    const char *fillmsg)
 {
     struct obj *objchain;
     struct monst *mon;
     boolean u_spot = u_at(x, y);
 
+    /* caller should have changed levl[x][y].typ to POOL, MOAT, or LAVA */
+    if (!is_pool_or_lava(x, y)) {
+        if (iflags.sanity_check) {
+            impossible("Insane liquid_flow(%d,%d,%s,%s).", x, y,
+                       ttmp ? trapname(ttmp->ttyp, TRUE) : "no trap",
+                       fillmsg ? fillmsg : "no mesg");
+        }
+        return;
+    }
+
     if (ttmp)
-        (void) delfloortrap(ttmp);
+        (void) delfloortrap(ttmp); /* will untrap monster is one is here */
     /* if any objects were frozen here, they're released now */
     unearth_objs(x, y);
 

src/music.c

@@ -1,4 +1,4 @@
-/* NetHack 3.7	music.c	$NHDT-Date: 1646688067 2022/03/07 21:21:07 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.77 $ */
+/* NetHack 3.7	music.c	$NHDT-Date: 1702206294 2023/12/10 11:04:54 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.101 $ */
 /*      Copyright (c) 1989 by Jean-Christophe Collet */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -337,8 +337,11 @@ do_earthquake(int force)
                    wand of digging if you alter this sequence. */
                 filltype = fillholetyp(x, y, FALSE);
                 if (filltype != ROOM) {
-                    levl[x][y].typ = filltype; /* flags set via doormask */
+                    set_levltyp(x, y, filltype); /* levl[x][y] = filltype; */
                     liquid_flow(x, y, filltype, chasm, (char *) 0);
+                    /* liquid_flow() deletes trap, might kill mtmp */
+                    if ((chasm = t_at(x, y)) == NULL)
+                        break; /* from switch, not loop */
                 }
 
                 mtmp = m_at(x, y); /* (redundant?) */
@@ -353,8 +356,8 @@ do_earthquake(int force)
                     break; /* from switch, not loop */
                 }
 
-                /* We have to check whether monsters or player
-                   falls in a chasm... */
+                /* We have to check whether monsters or hero falls into a
+                   new pit....  Note: if we get here, chasm is non-Null. */
                 if (mtmp) {
                     if (!is_flyer(mtmp->data) && !is_clinger(mtmp->data)) {
                         boolean m_already_trapped = mtmp->mtrapped;
@@ -427,7 +430,7 @@ do_earthquake(int force)
                             exercise(A_DEX, TRUE);
                         else
                             selftouch((Upolyd && (slithy(gy.youmonst.data)
-                                                  || nolimbs(gy.youmonst.data)))
+                                                || nolimbs(gy.youmonst.data)))
                                       ? "Shaken, you"
                                       : "Falling down, you");
                     }