add amla advancement to [modify_unit_type]

Addresses https://github.com/wesnoth/wesnoth/issues/9309
when used, the amlas in [unit_type] are replaced by list of amlas in [modify_unit_type],i cannot done add [advancement] without erase amla already present.

data/schema/core/addons.cfg

@@ -162,6 +162,9 @@
 		{SIMPLE_KEY set_advances_to string_list}
 		{SIMPLE_KEY set_cost int}
 		{SIMPLE_KEY set_experience int}
+		# link the advancement tag
+		# to enable AMLA support
+		{LINK_TAG "units/$modifications/advancement"}
 	[/tag]
 	{DATA_TAG "world_conquest_data" 0 1 any}
 [/tag]

data/test/scenarios/wml_tests/ScenarioWML/add_advancements.cfg

@@ -71,3 +71,47 @@
         {SUCCEED}
     [/event]
 )}
+
+#####
+# API(s) being tested: [modify_unit_type][advancement]
+##
+# Actions:
+# Modify the cavalier unit type to add add_level amla.
+# Spawn a cavalier unit.
+# Make advances cavalier
+##
+# Expected end state:
+# The spawned cavalier should have level=4.
+#####
+{GENERIC_UNIT_TEST "add_or_replace_amla" (
+    [modify_unit_type]
+        type="Cavalier"
+        [advancement]
+            id = add_level
+            [effect]
+                apply_to = level
+                increase=1
+            [/effect]
+        [/advancement]
+    [/modify_unit_type]
+    [event]
+        name=start
+        [unit]
+            x = 1
+            y = 1
+            type = Cavalier
+            side = 1
+            id = charlie
+            canrecruit = no
+        [/unit]
+        {ADVANCE_UNIT id=charlie ""}
+        [store_unit]
+            variable=cavalier
+            [filter]
+                id = charlie
+            [/filter]
+        [/store_unit]
+        {ASSERT ({VARIABLE_CONDITIONAL cavalier.level equals 4})}
+        {SUCCEED}
+    [/event]
+)}

src/units/types.cpp

@@ -86,6 +86,7 @@ unit_type::unit_type(const unit_type& o)
 	, hide_help_(o.hide_help_)
 	, do_not_list_(o.do_not_list_)
 	, advances_to_(o.advances_to_)
+	, advancements_(o.advancements_)
 	, experience_needed_(o.experience_needed_)
 	, alignment_(o.alignment_)
 	, movement_type_(o.movement_type_)
@@ -137,6 +138,7 @@ unit_type::unit_type(defaut_ctor_t, const config& cfg, const std::string & paren
 	, hide_help_(false)
 	, do_not_list_()
 	, advances_to_()
+	, advancements_(cfg.child_range("advancement"))
 	, experience_needed_(0)
 	, alignment_(unit_alignments::type::neutral)
 	, movement_type_()
@@ -1395,6 +1397,10 @@ void unit_type::apply_scenario_fix(const config& cfg)
 		}
 	}
 
+	if(cfg.has_child("advancement")) {
+		advancements_ = cfg.child_range("advancement");
+	}
+
 	// apply recursively to subtypes.
 	for(int gender = 0; gender <= 1; ++gender) {
 		if(!gender_types_[gender]) {
@@ -1444,6 +1450,7 @@ void unit_type::remove_scenario_fixes()
 	for(auto& v : variations_) {
 		v.second.remove_scenario_fixes();
 	}
+	advancements_ = get_cfg().child_range("advancement");
 }
 
 void unit_type_data::remove_scenario_fixes()

src/units/types.hpp

@@ -118,7 +118,7 @@ public:
 
 	/** Returns two iterators pointing to a range of AMLA configs. */
 	config::const_child_itors modification_advancements() const
-	{ return get_cfg().child_range("advancement"); }
+	{ return advancements_; }
 
 	/**
 	 * Returns a gendered variant of this unit_type.
@@ -235,7 +235,7 @@ public:
 	{ return get_cfg().child_or_empty("abilities"); }
 
 	config::const_child_itors advancements() const
-	{ return get_cfg().child_range("advancement"); }
+	{ return advancements_; }
 
 	config::const_child_itors events() const
 	{ return get_cfg().child_range("event"); }
@@ -364,6 +364,7 @@ private:
 	bool zoc_, hide_help_, do_not_list_;
 
 	std::vector<std::string> advances_to_;
+	config::const_child_itors advancements_;
 	int experience_needed_;
 
 

wml_test_schedule

@@ -231,6 +231,7 @@
 0 test_attacks_used
 0 no_duplicate_advancements
 0 add_advancement
+0 add_or_replace_amla
 0 harm_unit_survivable_experience_no
 0 harm_unit_survivable_experience_unset
 0 harm_unit_survivable_experience_yes