Revert "Bye bye clinging."

Clinging might be a minor feature, but it's a distinguishing one, it's thematic
and it's working quite well.
Player/monster symmetry has never been a goal, so it seems dubious to invoke it
as the reason to throw away all the work that has been put into clinging. We
can always say that the player turns into a different kind of spider which is
unable to cling for some reason.

This reverts commit bdc56382eacf7af1b2330dc6444916d368741fec.
This reverts commit d689486464fcaaac025a6f469ab69674a2f4d173.
This reverts commit 1addaaf8ee92de5060fdb436f93251843abd2035.

1 files changed, 10 insertions, 2 deletions

diff --git a/crawl-ref/source/mon-movetarget.cc b/crawl-ref/source/mon-movetarget.cc
index 0fbd37fdc7..d8003f6bdf 100644
--- a/crawl-ref/source/mon-movetarget.cc
+++ b/crawl-ref/source/mon-movetarget.cc
@@ -61,6 +61,10 @@ static void _mark_neighbours_target_unreachable(monster* mon)
         if (mons_primary_habitat(m) != habit)
             continue;
 
+        // Wall clinging monsters use different pathfinding.
+        if (mon->can_cling_to_walls() != m->can_cling_to_walls())
+            continue;
+
         // A flying monster has an advantage over a non-flying one.
         // Same for a swimming one.
         if (!flies && mons_flies(m)
@@ -171,9 +175,13 @@ bool try_pathfind(monster* mon)
 
     // If the target is "unreachable" (the monster already tried,
     // and failed, to find a path), there's a chance of trying again.
-    // Retreating monsters retry every turn.
-    if (target_is_unreachable(mon) && !one_chance_in(12))
+    // The chance is higher for wall clinging monsters to help them avoid
+    // shallow water. Retreating monsters retry every turn.
+    if (target_is_unreachable(mon) && !one_chance_in(12)
+        && !(mon->can_cling_to_walls() && one_chance_in(4)))
+    {
         return false;
+    }
 
 #ifdef DEBUG_PATHFIND
     mprf("%s: Player out of reach! What now?",