kick/joust monster positioning (trunk only)

From a 7.5 year old news posting (with a reply by Kevin Hugo speaking
on behalf of slash'em...):  when a monster "nimbly jumps to evade" hero's
kick, it can pass through walls and grid bugs can jump off their grid.
Likewise when a joust or staggering blow knocks a monster back, it could
move grid bugs diagonally.  This fixes both cases.

     Offhand I can't think of any other non-standard movement situations
which might need similar handling, but it wouldn't surprise me if there
are some.  Leashed movement is close but I don't think maybe_mnexto helps.

doc/fixes35.0

@@ -231,6 +231,8 @@ override non-silver vs shades for artifacts which deal extra damage to undead
 assorted mirror fixes--mainly visibility issues
 some monsters can't be strangled; self-polymorph can stop/restart strangulation
 re-adjust gem generation probabilities when revisiting existing dungeon levels
+kick evasion shouldn't move monsters through walls
+kick evasion and jousting/staggering blows shouldn't move grid bugs diagonally
 
 
 Platform- and/or Interface-Specific Fixes

include/extern.h

@@ -1289,6 +1289,7 @@ E void FDECL(killed, (struct monst *));
 E void FDECL(xkilled, (struct monst *,int));
 E void FDECL(mon_to_stone, (struct monst*));
 E void FDECL(mnexto, (struct monst *));
+E void FDECL(maybe_mnexto, (struct monst *));
 E boolean FDECL(mnearto, (struct monst *,XCHAR_P,XCHAR_P,BOOLEAN_P));
 E void FDECL(m_respond, (struct monst *));
 E void FDECL(setmangry, (struct monst *));

src/dokick.c

@@ -206,7 +206,7 @@ doit:
 		(void) passive(mon, FALSE, 1, AT_KICK, FALSE);
 		return;
 	    } else {
-		mnexto(mon);
+		maybe_mnexto(mon);
 		if(mon->mx != x || mon->my != y) {
 		    if(glyph_is_invisible(levl[x][y].glyph)) {
 			unmap_object(x, y);

src/dothrow.c

@@ -724,6 +724,8 @@ mhurtle(mon, dx, dy, range)
     dx = sgn(dx);
     dy = sgn(dy);
     if(!range || (!dx && !dy)) return; /* paranoia */
+    /* don't let grid bugs be hurtled diagonally */
+    if (dx && dy && NODIAG(monsndx(mon->data))) return;
 
 	/* Send the monster along the path */
 	mc.x = mon->mx;

src/mon.c

@@ -2121,6 +2121,7 @@ mon_to_stone(mtmp)
 	impossible("Can't polystone %s!", a_monnam(mtmp));
 }
 
+/* might place monst on far side of a wall or boulder */
 void
 mnexto(mtmp)	/* Make monster mtmp next to you (if possible) */
 	struct monst *mtmp;
@@ -2148,6 +2149,27 @@ mnexto(mtmp)	/* Make monster mtmp next to you (if possible) */
 	return;
 }
 
+/* like mnexto() but requires destination to be directly accessible */
+void
+maybe_mnexto(mtmp)
+struct monst *mtmp;
+{
+	coord mm;
+	struct permonst *ptr = mtmp->data;
+	boolean diagok = !NODIAG(ptr - mons);
+	int tryct = 20;
+
+	do {
+	    if (!enexto(&mm, u.ux, u.uy, ptr)) return;
+	    if (couldsee(mm.x, mm.y) &&
+		    /* don't move grid bugs diagonally */
+		    (diagok || mm.x == mtmp->mx || mm.y == mtmp->my)) {
+		rloc_to(mtmp, mm.x, mm.y);
+		return;
+	    }
+	} while (--tryct > 0);
+}
+
 /* mnearto()
  * Put monster near (or at) location if possible.
  * Returns: