Fast Micro AI: add [filter] and [filter_second] tags

These can be used to limit the attackers and attack targets in the same
way as the ‘attacks’ facet does with [filter_own] and [filter_enemy]
for the default AI combat candidate action.
This does not affect the move-to-targets candidate action of the Fast
Micro AI.

data/ai/micro_ais/cas/ca_fast_combat.lua

@@ -10,7 +10,10 @@ function ca_fast_combat:evaluation(ai, cfg, self)
     self.data.gamedata = FAU.gamedata_setup()
 
     if (not self.data.fast_combat_units) or (not self.data.fast_combat_units[1]) then
-        self.data.fast_combat_units = wesnoth.get_units { side = wesnoth.current.side }
+        self.data.fast_combat_units = wesnoth.get_units {
+            side = wesnoth.current.side,
+            { "and", cfg.filter }
+        }
         if (not self.data.fast_combat_units[1]) then return 0 end
 
         -- For speed reasons, we'll go through the arrays from the end, so they are sorted backwards
@@ -21,8 +24,21 @@ function ca_fast_combat:evaluation(ai, cfg, self)
         end
     end
 
-    -- Exclude hidden enemies, except if attack_hidden_enemies=yes is set in [micro_ai] tag
     local excluded_enemies_map = LS.create()
+
+    -- Exclude enemies not matching [filter_second]
+    if (cfg.filter_second) then
+        local excluded_enemies = wesnoth.get_units {
+            { "filter_side", { { "enemy_of", { side = wesnoth.current.side } } } },
+            { "not", cfg.filter_second }
+        }
+
+        for _,e in ipairs(excluded_enemies) do
+            excluded_enemies_map:insert(e.x, e.y)
+        end
+    end
+
+    -- Exclude hidden enemies, except if attack_hidden_enemies=yes is set in [micro_ai] tag
     if (not cfg.attack_hidden_enemies) then
         local hidden_enemies = wesnoth.get_units {
             { "filter_side", { { "enemy_of", { side = wesnoth.current.side } } } },

data/ai/micro_ais/micro_ai_wml_tag.lua

@@ -460,7 +460,8 @@ function wesnoth.wml_actions.micro_ai(cfg)
 
     elseif (cfg.ai_type == 'fast_ai') then
         optional_keys = {
-            "attack_hidden_enemies", "dungeon_mode", "include_occupied_attack_hexes", "move_cost_factor",
+            "attack_hidden_enemies", "dungeon_mode", "filter", "filter_second",
+            "include_occupied_attack_hexes", "move_cost_factor",
             "weak_units_first", "skip_combat_ca", "skip_move_ca"
         }
         CA_parms = {