fix(reg): Include explicitly specified fonts in info.plist for backward compatibilty

Author: jeromelaban

src/SourceGenerators/Uno.UI.Tasks/Assets/RetargetAssets.Fonts.cs

@@ -3,6 +3,7 @@
 using System.Diagnostics;
 using System.IO;
 using System.Linq;
+using System.Xml;
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
 using Uno.UI.Tasks.Helpers;
@@ -31,10 +32,15 @@ public partial class RetargetAssets_v0
 		</plist>
 		""";
 
-	private ITaskItem[] GenerateFontPartialManifest(List<string> fontAssets)
+	private ITaskItem[] GenerateFontPartialManifest(List<string> fontAssets, string iOSAppManifest)
 	{
 		if (TargetPlatform == "ios")
 		{
+			// For compatibility measures, get the fonts from the iOS app manifest
+			// and merge them with the generated ones, so existing apps don't lose
+			// explicitly specified ones.
+			var existingFonts = EnumerateFontsFromPList(IosAppManifest);
+
 			var outputManifestFile = Path.Combine(IntermediateOutputPath, "FontsPartialInfo.plist");
 
 			using var writer = File.CreateText(outputManifestFile);
@@ -46,7 +52,7 @@ private ITaskItem[] GenerateFontPartialManifest(List<string> fontAssets)
 				writer.WriteLine("  <key>UIAppFonts</key>");
 				writer.WriteLine("  <array>");
 
-				foreach (var font in fontAssets)
+				foreach (var font in fontAssets.Concat(existingFonts))
 				{
 					writer.WriteLine("    <string>" + font + "</string>");
 				}
@@ -63,4 +69,17 @@ private ITaskItem[] GenerateFontPartialManifest(List<string> fontAssets)
 			return Array.Empty<ITaskItem>();
 		}
 	}
+
+	private string[] EnumerateFontsFromPList(string iosAppManifest)
+	{
+		XmlDocument doc = new();
+		doc.Load(iosAppManifest);
+
+		// Get the list of registered fonts in the info.plist
+		return doc
+			.SelectNodes("//key[text()='UIAppFonts']/following-sibling::array[1]/string")
+			.OfType<XmlNode>()
+			.Select(n => n.InnerText)
+			.ToArray();
+	}
 }

src/SourceGenerators/Uno.UI.Tasks/Assets/RetargetAssets.cs

@@ -31,6 +31,8 @@ public partial class RetargetAssets_v0 : Task
 
 		public string AndroidAssetsPrefix { get; set; }
 
+		public string IosAppManifest { get; set; }
+
 		[Required]
 		public string DefaultLanguage { get; set; }
 
@@ -169,7 +171,7 @@ private void ProcessContentItems(ITaskItem[] assets, Func<ResourceCandidate, str
 			}
 
 			RetargetedAssets = retargetdAssets.ToArray();
-			PartialAppManifests = GenerateFontPartialManifest(fontAssets);
+			PartialAppManifests = GenerateFontPartialManifest(fontAssets, IosAppManifest);
 		}
 
 

src/SourceGenerators/Uno.UI.Tasks/Content/Uno.UI.Tasks.targets

@@ -128,6 +128,7 @@
 							IntermediateOutputPath="$(IntermediateOutputPath)"
 							ContentItems="@(Content);@(_SourceItemsToCopyToOutputDirectory)"
 							AndroidAssetsPrefix="$(MonoAndroidAssetsPrefix)"
+							IosAppManifest="$(AppBundleManifest)"
 							Condition="'$(XamarinProjectType)'!=''">
 			<Output TaskParameter="Assets"
 							ItemName="Assets" />