fix #H6042 - leash use while engulfed

Prevent using a leash while engulfed.  If someone wants to supply a
better message, go ahead.  I just tried to get the logic straight.
(The new swallowed part is easy; the previous lack of handling for
remembered unseen monsters wasn't quite so easy.)

Applying a leash was always using a move, even if player cancelled
at the prompt to pick an adjacent monster.  Now some of the early
exits don't use a move.

doc/fixes36.1

@@ -434,6 +434,9 @@ when returning to quest nemesis' level, the message for some roles (A,S,T,W)
 when the Amulet increased spell casting cost, nothing actually happened (aside
 	from the message about feeling the Amulet drain the hero's power) if
 	hero lacked sufficient energy to cast the spell
+if was possible to leash an adjacent pet while engulfed
+if leash or unleash attempt was directed at "remembered, unseen monster" glyph
+	and yielded "there's no creature there", the glyph wasn't removed
 
 
 Fixes to Post-3.6.0 Problems that Were Exposed Via git Repository

src/apply.c

@@ -12,7 +12,7 @@ STATIC_DCL boolean FDECL(its_dead, (int, int, int *));
 STATIC_DCL int FDECL(use_stethoscope, (struct obj *));
 STATIC_DCL void FDECL(use_whistle, (struct obj *));
 STATIC_DCL void FDECL(use_magic_whistle, (struct obj *));
-STATIC_DCL void FDECL(use_leash, (struct obj *));
+STATIC_DCL int FDECL(use_leash, (struct obj *));
 STATIC_DCL int FDECL(use_mirror, (struct obj *));
 STATIC_DCL void FDECL(use_bell, (struct obj **));
 STATIC_DCL void FDECL(use_candelabrum, (struct obj *));
@@ -573,6 +573,10 @@ unleash_all()
 
 #define MAXLEASHED 2
 
+/* TODO:
+ *  This ought to exclude various other things, such as lights and gas
+ *  spore, is_whirly() critters, ethereal creatures, possibly others.
+ */
 static boolean
 leashable(mtmp)
 struct monst *mtmp;
@@ -581,82 +585,102 @@ struct monst *mtmp;
 }
 
 /* ARGSUSED */
-STATIC_OVL void
+STATIC_OVL int
 use_leash(obj)
 struct obj *obj;
 {
     coord cc;
-    register struct monst *mtmp;
+    struct monst *mtmp;
     int spotmon;
 
+    if (u.uswallow) {
+        /* if the leash isn't in use, assume we're trying to leash
+           the engulfer; if it is use, distinguish between removing
+           it from the engulfer versus from some other creature
+           (note: the two in-use cases can't actually occur; all
+           leashes are released when the hero gets engulfed) */
+        You_cant((!obj->leashmon
+                  ? "leash %s from inside."
+                  : (obj->leashmon == (int) u.ustuck->m_id)
+                    ? "unleash %s from inside."
+                    : "unleash anything from inside %s."),
+                 noit_mon_nam(u.ustuck));
+        return 0;
+    }
     if (!obj->leashmon && number_leashed() >= MAXLEASHED) {
         You("cannot leash any more pets.");
-        return;
+        return 0;
     }
 
     if (!get_adjacent_loc((char *) 0, (char *) 0, u.ux, u.uy, &cc))
-        return;
+        return 0;
 
-    if ((cc.x == u.ux) && (cc.y == u.uy)) {
+    if (cc.x == u.ux && cc.y == u.uy) {
         if (u.usteed && u.dz > 0) {
             mtmp = u.usteed;
             spotmon = 1;
             goto got_target;
         }
         pline("Leash yourself?  Very funny...");
-        return;
+        return 0;
     }
 
+    /*
+     * From here on out, return value is 1 == a move is used.
+     */
+
     if (!(mtmp = m_at(cc.x, cc.y))) {
         There("is no creature there.");
-        return;
+        if (glyph_is_invisible(levl[cc.x][cc.y].glyph)) {
+            unmap_object(cc.x, cc.y);
+            newsym(cc.x, cc.y);
+        }
+        return 1;
     }
 
     spotmon = canspotmon(mtmp);
-got_target:
+ got_target:
 
-    if (!mtmp->mtame) {
+    if (!spotmon && !glyph_is_invisible(levl[cc.x][cc.y].glyph)) {
-        if (!spotmon)
+        /* for the unleash case, we don't verify whether this unseen
-            There("is no creature there.");
+           monster is the creature attached to the current leash */
-        else
+        You("fail to %sleash something.", obj->leashmon ? "un" : "");
-            pline("%s %s leashed!", Monnam(mtmp),
+        /* trying again will work provided the monster is tame
-                  (!obj->leashmon) ? "cannot be" : "is not");
+           (and also that it doesn't change location by retry time) */
-        return;
+        map_invisible(cc.x, cc.y);
-    }
+    } else if (!mtmp->mtame) {
-    if (!obj->leashmon) {
+        pline("%s %s leashed!", Monnam(mtmp),
+              (!obj->leashmon) ? "cannot be" : "is not");
+    } else if (!obj->leashmon) {
+        /* applying a leash which isn't currently in use */
         if (mtmp->mleashed) {
             pline("This %s is already leashed.",
-                  spotmon ? l_monnam(mtmp) : "monster");
+                  spotmon ? l_monnam(mtmp) : "creature");
-            return;
+        } else if (!leashable(mtmp)) {
-        }
-        if (!leashable(mtmp)) {
             pline("The leash won't fit onto %s%s.", spotmon ? "your " : "",
                   l_monnam(mtmp));
-            return;
+        } else {
+            You("slip the leash around %s%s.", spotmon ? "your " : "",
+                l_monnam(mtmp));
+            mtmp->mleashed = 1;
+            obj->leashmon = (int) mtmp->m_id;
+            mtmp->msleeping = 0;
         }
-
-        You("slip the leash around %s%s.", spotmon ? "your " : "",
-            l_monnam(mtmp));
-        mtmp->mleashed = 1;
-        obj->leashmon = (int) mtmp->m_id;
-        mtmp->msleeping = 0;
-        return;
-    }
-    if (obj->leashmon != (int) mtmp->m_id) {
-        pline("This leash is not attached to that creature.");
-        return;
     } else {
-        if (obj->cursed) {
+        /* applying a leash which is currently in use */
+        if (obj->leashmon != (int) mtmp->m_id) {
+            pline("This leash is not attached to that creature.");
+        } else if (obj->cursed) {
             pline_The("leash would not come off!");
-            obj->bknown = TRUE;
+            obj->bknown = 1;
-            return;
+        } else {
+            mtmp->mleashed = 0;
+            obj->leashmon = 0;
+            You("remove the leash from %s%s.",
+                spotmon ? "your " : "", l_monnam(mtmp));
         }
-        mtmp->mleashed = 0;
-        obj->leashmon = 0;
-        You("remove the leash from %s%s.", spotmon ? "your " : "",
-            l_monnam(mtmp));
     }
-    return;
+    return 1;
 }
 
 /* assuming mtmp->mleashed has been checked */
@@ -3555,7 +3579,7 @@ doapply()
         use_tinning_kit(obj);
         break;
     case LEASH:
-        use_leash(obj);
+        res = use_leash(obj);
         break;
     case SADDLE:
         res = use_saddle(obj);