[TrimmableTypeMap] Keep user AndroidJavaSource Java under R8 shrinking

src/Xamarin.Android.Build.Tasks/Tasks/R8.cs

@@ -37,6 +37,10 @@ public class R8 : D8
 		public ITaskItem []? ProguardConfigurationFiles { get; set; }
 		public bool UseTrimmableNativeAotProguardConfiguration { get; set; }
 
+		// User-authored AndroidJavaSource (Bind != true) .java files. These have no managed peer and are
+		// therefore absent from the acw-map, so they must be kept explicitly when shrinking is enabled.
+		public ITaskItem []? JavaSourceFiles { get; set; }
+
 		protected override string MainClass => "com.android.tools.r8.R8";
 
 		readonly List<string> tempFiles = new List<string> ();
@@ -52,6 +56,52 @@ public override bool RunTask ()
 			}
 		}
 
+		// Derive the fully-qualified Java type name from each user .java source file. Java requires the
+		// public top-level type name to match the file name, so '<package>.<FileNameWithoutExtension>' is
+		// the type to keep. Files that no longer exist are skipped.
+		IEnumerable<string> GetUserJavaTypes ()
+		{
+			if (JavaSourceFiles == null) {
+				yield break;
+			}
+			var seen = new HashSet<string> (StringComparer.Ordinal);
+			foreach (var item in JavaSourceFiles) {
+				var path = item.ItemSpec;
+				if (path.IsNullOrEmpty () || !File.Exists (path)) {
+					continue;
+				}
+				var typeName = Path.GetFileNameWithoutExtension (path);
+				var package = ReadJavaPackage (path);
+				if (!package.IsNullOrEmpty ()) {
+					typeName = $"{package}.{typeName}";
+				}
+				if (seen.Add (typeName)) {
+					yield return typeName;
+				}
+			}
+		}
+
+		static string? ReadJavaPackage (string path)
+		{
+			foreach (var raw in File.ReadLines (path)) {
+				var line = raw.Trim ();
+				if (line.Length == 0 || line.StartsWith ("//", StringComparison.Ordinal) || line.StartsWith ("*", StringComparison.Ordinal) || line.StartsWith ("/*", StringComparison.Ordinal)) {
+					continue;
+				}
+				if (line.StartsWith ("package ", StringComparison.Ordinal)) {
+					var end = line.IndexOf (';');
+					if (end > "package ".Length) {
+						return line.Substring ("package ".Length, end - "package ".Length).Trim ();
+					}
+				}
+				// The package declaration, if present, must precede any type declaration.
+				if (line.StartsWith ("import ", StringComparison.Ordinal) || line.Contains ("class ") || line.Contains ("interface ") || line.Contains ("enum ")) {
+					break;
+				}
+			}
+			return null;
+		}
+
 		/// <summary>
 		/// Override CreateResponseFile to add R8-specific arguments to the response file.
 		/// This ensures all arguments are passed via response file to avoid command line length limits.
@@ -109,6 +159,11 @@ protected override string CreateResponseFile ()
 						foreach (var java in javaTypes) {
 							appcfg.WriteLine ($"-keep class {java} {{ *; }}");
 						}
+						// User-authored AndroidJavaSource (Bind != true) has no managed peer and is absent
+						// from the acw-map, so keep it explicitly; otherwise shrinking removes it.
+						foreach (var java in GetUserJavaTypes ()) {
+							appcfg.WriteLine ($"-keep class {java} {{ *; }}");
+						}
 					}
 				}
 				if (!ProguardCommonXamarinConfiguration.IsNullOrWhiteSpace ()) {

src/Xamarin.Android.Build.Tasks/Xamarin.Android.D8.targets

@@ -51,6 +51,9 @@ Copyright (C) 2018 Xamarin. All rights reserved.
     <ItemGroup>
       <_AndroidD8MapDiagnostics Condition=" '$(AndroidD8IgnoreWarnings)' == 'true' " Include="warning" To="info" />
       <_AndroidR8MapDiagnostics Condition=" '$(AndroidR8IgnoreWarnings)' == 'true' " Include="warning" To="info" />
+      <!-- User-authored AndroidJavaSource (Bind != True) is not in the acw-map; pass it to R8 so it
+           is kept when shrinking is enabled rather than silently removed. -->
+      <_R8KeepJavaSource Include="@(AndroidJavaSource)" Condition=" '%(AndroidJavaSource.Bind)' != 'True' " />
     </ItemGroup>
 
     <R8
@@ -69,6 +72,7 @@ Copyright (C) 2018 Xamarin. All rights reserved.
         EnableDesugar="$(AndroidEnableDesugar)"
         AndroidSdkBuildToolsPath="$(AndroidSdkBuildToolsPath)"
         AcwMapFile="$(_AcwMapFile)"
+        JavaSourceFiles="@(_R8KeepJavaSource)"
         ProguardCommonXamarinConfiguration="$(IntermediateOutputPath)proguard\proguard_xamarin.cfg"
         ProguardGeneratedReferenceConfiguration="$(_ProguardProjectConfiguration)"
         ProguardGeneratedApplicationConfiguration="$(IntermediateOutputPath)proguard\proguard_project_primary.cfg"