Clear the subvault stack on each placement attempt

This fixes a rare corner case (#7435) where a vault's subvaults could be
placed correctly while the vault itself is not, causing the builder to
fail to place its subvaults on subsequent attempts.

Also add a debug message for when the validate lua call fails.

1 files changed, 6 insertions, 3 deletions

diff --git a/crawl-ref/source/maps.cc b/crawl-ref/source/maps.cc
index d1b192e40e..0eebfd02ea 100644
--- a/crawl-ref/source/maps.cc
+++ b/crawl-ref/source/maps.cc
@@ -118,9 +118,6 @@ static map_section_type _write_vault(map_def &mdef,
                                      vault_placement &place,
                                      bool check_place)
 {
-    // We're a regular vault, so clear the subvault stack.
-    clear_subvault_stack();
-
     mdef.load();
 
     // Copy the map so we can monkey with it.
@@ -134,6 +131,9 @@ static map_section_type _write_vault(map_def &mdef,
 
     while (tries-- > 0)
     {
+        // We're a regular vault, so clear the subvault stack.
+        clear_subvault_stack();
+
         if (place.map.test_lua_veto())
             break;
 
@@ -189,7 +189,10 @@ static bool _resolve_map_lua(map_def &map)
     }
 
     if (!map.test_lua_validate(false))
+    {
+        dprf("Lua validation for map %s failed.", map.name.c_str());
         return false;
+    }
 
     return true;
 }