buglist - full level triggers impossible() from migrating mons

<email deleted> wrote:
> If more monsters fall through a trap door than can fit on the
> level below, when you go down the stairs, you get the following
> message:
>  "Program in disorder - perhaps you'd better #quit.
>  rloc(): couldn't relocate monster"
> This message seems to appear once for every monster-too-many that
> fell through the hole. I originally found this while
> intentionally completely filling a level with black puddings
> (there was a trap door I didn't know about). I also confirmed it
> in a wiz-mode test using gremlins and water.

[confirmed: moveloop -> deferred_goto -> goto_level ->
 losedogs -> mon_arrive -> rloc -> impossible]

This patch:
- causes rloc() to return TRUE if successful,
  or FALSE if it wasn't.
- adds code to mon_arrive() in dog.c to deal with
  the failed rloc()
- allows the x,y parameters to mkcorpstat() to
  be 0,0 in order to trigger random placement of the
  corpse on the level
- if you define DEBUG_MIGRATING_MONS when you build cmd.c
  then you'll have a debug-mode command #migratemons to
  store the number of random monsters that you specify
  on the migrating monsters chain.

src/teleport.c

@@ -953,16 +953,18 @@ register int x, y;
 }
 
 /* place a monster at a random location, typically due to teleport */
-void
-rloc(mtmp)
+/* return TRUE if successful, FALSE if not */
+boolean
+rloc(mtmp, suppress_impossible)
 struct monst *mtmp;	/* mx==0 implies migrating monster arrival */
+boolean suppress_impossible;
 {
 	register int x, y, trycount;
 
 #ifdef STEED
 	if (mtmp == u.usteed) {
 	    tele();
-	    return;
+	    return TRUE;
 	}
 #endif
 
@@ -996,11 +998,13 @@ struct monst *mtmp;	/* mx==0 implies migrating monster arrival */
 		    goto found_xy;
 
 	/* level either full of monsters or somehow faulty */
-	impossible("rloc(): couldn't relocate monster");
-	return;
+	if (!suppress_impossible)
+		impossible("rloc(): couldn't relocate monster");
+	return FALSE;
 
  found_xy:
 	rloc_to(mtmp, x, y);
+	return TRUE;
 }
 
 STATIC_OVL void
@@ -1015,7 +1019,7 @@ struct monst *mtmp;
 		rloc_to(mtmp, c.x, c.y);
 		return;
 	}
-	rloc(mtmp);
+	(void) rloc(mtmp, FALSE);
 }
 
 boolean
@@ -1049,7 +1053,7 @@ int in_sight;
 	     * the guard isn't going to come for it...
 	     */
 	    if (trap->once) mvault_tele(mtmp);
-	    else rloc(mtmp);
+	    else (void) rloc(mtmp, FALSE);
 
 	    if (in_sight) {
 		if (canseemon(mtmp))
@@ -1253,12 +1257,12 @@ boolean give_feedback;
 	    if (give_feedback)
 		You("are no longer inside %s!", mon_nam(mtmp));
 	    unstuck(mtmp);
-	    rloc(mtmp);
+	    (void) rloc(mtmp, FALSE);
 	} else if (is_rider(mtmp->data) && rn2(13) &&
 		   enexto(&cc, u.ux, u.uy, mtmp->data))
 	    rloc_to(mtmp, cc.x, cc.y);
 	else
-	    rloc(mtmp);
+	    (void) rloc(mtmp, FALSE);
 	return TRUE;
 }