Fix landed title definitions from multiple files not being correctly merged

ImperatorToCK3.UnitTests/CK3/Titles/LandedTitlesTests.cs

@@ -582,4 +582,29 @@ public void GetBaronyForProvinceReturnsCorrectBaronyOrNullWhenNotFound() {
 		Assert.Equal("b_barony3", titles.GetBaronyForProvince(3)?.Id);
 		Assert.Null(titles.GetBaronyForProvince(4));
 	}
-}
+
+	[Fact]
+	public void TitlesCanBeExpandedInOtherFiles() {
+		var titles = new Title.LandedTitles();
+		titles.LoadTitles(ck3ModFS, new TestCK3LocDB());
+
+		// e_mongolia's color is defined in base_landed_titles.txt.
+		// But its capital is defined in extra_landed_titles.txt.
+		// If both are properly set, it means that we're correctly loading a title from multiple files.
+		var mongoliaEmpire = titles["e_mongolia"];
+		Assert.Equal(new Color(90, 90, 240), mongoliaEmpire.Color1);
+		Assert.Equal("c_karakorum", mongoliaEmpire.CapitalCountyId);
+
+		// It has k_mongolia and k_angara defined as de jure vassals in base_landed_titles.txt.
+		// It also has k_jubu defined as a de jure vassal in extra_landed_titles.txt.
+		Assert.Equal(3, mongoliaEmpire.DeJureVassals.Count);
+
+		// k_mongolia's color is defined in base_landed_titles.txt.
+		// But its capital is defined in extra_landed_titles.txt.
+		// This checks if we can correctly load lower rank titles (nested in the structure) from multiple files.
+		var mongoliaKingdom = titles["k_mongolia"];
+		Assert.Equal(new Color(20, 65, 25), mongoliaKingdom.Color1);
+		Assert.Equal("c_karakorum", mongoliaKingdom.CapitalCountyId);
+	}
+}
+

ImperatorToCK3.UnitTests/TestFiles/LandedTitlesTests/CK3/game/common/landed_titles/base_landed_titles.txt

@@ -0,0 +1,9 @@
+e_mongolia = {
+	color = { 90 90 240 }
+
+	k_mongolia = {
+		color = { 20 65 25 }
+	}
+
+	k_angara = {}
+}

ImperatorToCK3.UnitTests/TestFiles/LandedTitlesTests/CK3/game/common/landed_titles/extra_landed_titles.txt

@@ -0,0 +1,9 @@
+e_mongolia = {
+	capital = c_karakorum
+
+	k_mongolia = {
+		capital = c_karakorum
+	}
+
+	k_jubu = {}
+}

ImperatorToCK3/CK3/Titles/LandedTitles.cs

@@ -119,9 +119,14 @@ private void RegisterKeys(Parser parser) {
 				Variables[variableName[1..]] = variableValue;
 			});
 			parser.RegisterRegex(Regexes.TitleId, (reader, titleNameStr) => {
-				// Pull the titles beneath this one and add them to the lot, overwriting existing ones.
-				var newTitle = Add(titleNameStr);
-				newTitle.LoadTitles(reader);
+				// Pull the titles beneath this one and add them to the lot.
+				// A title can be defined in multiple files, in that case merge the definitions.
+				if (TryGetValue(titleNameStr, out var titleToUpdate)) {
+					titleToUpdate.LoadTitles(reader);
+				} else {
+					var newTitle = Add(titleNameStr);
+					newTitle.LoadTitles(reader);
+				}
 			});
 			parser.IgnoreAndLogUnregisteredItems();
 		}
@@ -221,8 +226,7 @@ ImperatorRegionMapper imperatorRegionMapper
 		}
 		public override void Remove(string name) {
 			if (dict.TryGetValue(name, out var titleToErase)) {
-				var deJureLiege = titleToErase.DeJureLiege;
-				deJureLiege?.DeJureVassals.Remove(name);
+				titleToErase.DeJureLiege = null; // Remove two-way liege-vassal link.
 
 				foreach (var vassal in titleToErase.DeJureVassals) {
 					vassal.DeJureLiege = null;

ImperatorToCK3/CK3/Titles/Title.cs

@@ -940,9 +940,9 @@ public Title? DeJureLiege { // direct de jure liege title
 				Logger.Warn($"Cannot set de jure liege {value} to {Id}: rank is not higher!");
 				return;
 			}
-			deJureLiege?.DeJureVassals.Remove(Id);
+			deJureLiege?.deJureVassals.Remove(Id);
 			deJureLiege = value;
-			value?.DeJureVassals.AddOrReplace(this);
+			value?.deJureVassals.AddOrReplace(this);
 		}
 	}
 	public Title? GetDeFactoLiege(Date date) { // direct de facto liege title
@@ -978,7 +978,8 @@ public void SetDeFactoLiege(Title? newLiege, Date date) {
 		}
 	}
 
-	[SerializeOnlyValue] public TitleCollection DeJureVassals { get; } = new(); // DIRECT de jure vassals
+	private readonly TitleCollection deJureVassals = [];
+	[SerializeOnlyValue] public IReadOnlyTitleCollection DeJureVassals => deJureVassals; // DIRECT de jure vassals
 	public IDictionary<string, Title> GetDeJureVassalsAndBelow() {
 		return GetDeJureVassalsAndBelow("bcdke");
 	}
@@ -1090,16 +1091,21 @@ public ICollection<string> GetSuccessionLaws(Date date) {
 
 	private void RegisterKeys(Parser parser) {
 		parser.RegisterRegex(Regexes.TitleId, (reader, titleNameStr) => {
-			// Pull the titles beneath this one and add them to the lot, overwriting existing ones.
-			var newTitle = parentCollection.Add(titleNameStr);
-			newTitle.LoadTitles(reader);
+			// Pull the titles beneath this one and add them to the lot.
+			// A title can be defined in multiple files, in that case merge the definitions.
+			if (parentCollection.TryGetValue(titleNameStr, out var childTitle)) {
+				childTitle.LoadTitles(reader);
+			} else {
+				childTitle = parentCollection.Add(titleNameStr);
+				childTitle.LoadTitles(reader);
+			}
 
-			if (newTitle.Rank == TitleRank.barony && string.IsNullOrEmpty(CapitalBaronyId)) {
+			if (childTitle.Rank == TitleRank.barony && string.IsNullOrEmpty(CapitalBaronyId)) {
 				// title is a barony, and no other barony has been found in this scope yet
-				CapitalBaronyId = newTitle.Id;
+				CapitalBaronyId = childTitle.Id;
 			}
-
-			newTitle.DeJureLiege = this;
+			
+			childTitle.DeJureLiege = this;
 		});
 		parser.RegisterKeyword("definite_form", reader => HasDefiniteForm = reader.GetBool());
 		parser.RegisterKeyword("ruler_uses_title_name", reader => RulerUsesTitleName = reader.GetBool());

ImperatorToCK3/CK3/Titles/TitleCollection.cs

@@ -1,5 +1,10 @@
 using commonItems.Collections;
+using System.Collections.Generic;
 
 namespace ImperatorToCK3.CK3.Titles;
 
-public class TitleCollection : IdObjectCollection<string, Title>;
+public interface IReadOnlyTitleCollection : IReadOnlyCollection<Title> {
+	public bool ContainsKey(string key);
+}
+
+public class TitleCollection : IdObjectCollection<string, Title>, IReadOnlyTitleCollection;