[Xamarin.Android.Build.Tasks] Generate R8 JNI remapping tables

Documentation/docs-mobile/TOC.yml

@@ -390,6 +390,10 @@
         href: messages/xa4323.md
       - name: XA4324
         href: messages/xa4324.md
+      - name: XA4325
+        href: messages/xa4325.md
+      - name: XA4326
+        href: messages/xa4326.md
       - name: XA4327
         href: messages/xa4327.md
       - name: XA4328

Documentation/docs-mobile/messages/index.md

@@ -266,6 +266,8 @@ Either change the value in the AndroidManifest.xml to match the $(SupportedOSPla
 + [XA4322](xa4322.md): Skipping library ProGuard configuration file '{file}' (from {source}) because it contains the unsupported global option '{option}'. Global ProGuard options are only allowed in application projects.
 + [XA4323](xa4323.md): Ignoring directory '{directory}' as it does not exist.
 + [XA4324](xa4324.md): [{arch}] Unable to delete source file '{file}'.
++ [XA4325](xa4325.md): Failed to generate the R8 JNI remapping data. {0}
++ [XA4326](xa4326.md): The R8 JNI remapping data is incomplete. {0}
 + [XA4327](xa4327.md): Could not extract Java type map keys from '{0}': {1}
 + [XA4328](xa4328.md): Could not generate typemap ProGuard configuration from '{0}': {1}
 

Documentation/docs-mobile/messages/xa4325.md

@@ -0,0 +1,29 @@
+---
+title: .NET for Android error XA4325
+description: XA4325 error code
+ms.date: 09/30/2026
+f1_keywords:
+  - "XA4325"
+---
+
+# .NET for Android error XA4325
+
+## Example message
+
+```
+error XA4325: Failed to generate the R8 JNI remapping data. The R8 mapping file 'mapping.txt' was not found.
+```
+
+## Issue
+
+The build could not generate runtime JNI remapping data from the final R8
+mapping. The mapping, linked managed metadata, or NativeAOT retention object
+is missing, unreadable, malformed, or contains entries that cannot be
+represented unambiguously by the runtime lookup tables.
+
+## Solution
+
+Fix the reported input path or earlier build failure. If the files were
+generated by .NET for Android, clean and rebuild the application. If the
+error reports ambiguous entries, use R8 keep rules so the affected Java
+classes or members are not merged into the same runtime lookup key.

Documentation/docs-mobile/messages/xa4326.md

@@ -0,0 +1,28 @@
+---
+title: .NET for Android warning XA4326
+description: XA4326 warning code
+ms.date: 09/30/2026
+f1_keywords:
+  - "XA4326"
+---
+
+# .NET for Android warning XA4326
+
+## Example message
+
+```
+warning XA4326: The R8 JNI remapping data is incomplete. The entry for 'example/Peer.run' was not emitted.
+```
+
+## Issue
+
+The build omitted an R8 JNI remapping entry because another remapping input
+already owns the same lookup key, or because a Java member signature could
+not be converted to a JNI descriptor. The runtime remapping data can
+therefore be incomplete for the affected type or member.
+
+## Solution
+
+Review the reported remapping inputs and Java signature. Remove conflicting
+custom remapping entries, correct malformed signatures, or add R8 keep rules
+for the affected Java type or member.

src/Xamarin.Android.Build.Tasks/Properties/Resources.resx

@@ -838,6 +838,93 @@ Remove the '{0}' reference from your project and add the '{1}' NuGet package ins
     <value>[{0}] Unable to delete source file '{1}'</value>
     <comment>{0} - The target architecture, such as Arm, Arm64, or X86_64
 {1} - The path to the source file which could not be deleted.</comment>
+  </data>
+  <data name="XA4325" xml:space="preserve">
+    <value>Failed to generate the R8 JNI remapping data. {0}</value>
+    <comment>The following are literal names and should not be translated: R8, JNI.
+{0} - A sentence describing the specific failure.</comment>
+  </data>
+  <data name="XA4325_MappingNotFound" xml:space="preserve">
+    <value>The R8 mapping file '{0}' was not found.</value>
+    <comment>The following is a literal name and should not be translated: R8.
+{0} - The path of the missing mapping file.</comment>
+  </data>
+  <data name="XA4325_MappingDataFailure" xml:space="preserve">
+    <value>The R8 mapping file '{0}' could not be read: {1}</value>
+    <comment>The following is a literal name and should not be translated: R8.
+{0} - The path of the mapping file.
+{1} - The exception message.</comment>
+  </data>
+  <data name="XA4325_AssemblyReadFailure" xml:space="preserve">
+    <value>The linked managed assembly '{0}' could not be read: {1}</value>
+    <comment>{0} - The path of the managed assembly.
+{1} - The exception message.</comment>
+  </data>
+  <data name="XA4325_AssemblyNotFound" xml:space="preserve">
+    <value>The linked managed assembly '{0}' was not found.</value>
+    <comment>{0} - The path of the missing managed assembly.</comment>
+  </data>
+  <data name="XA4325_AssemblyHasNoMetadata" xml:space="preserve">
+    <value>The linked managed assembly '{0}' does not contain managed metadata.</value>
+    <comment>{0} - The path of the input file.</comment>
+  </data>
+  <data name="XA4325_AmbiguousEntry" xml:space="preserve">
+    <value>The generated '{0}' entries for '{1}' have conflicting runtime targets '{2}' and '{3}', which cannot be represented by the JNI remapping tables.</value>
+    <comment>The following is a literal name and should not be translated: JNI.
+{0} - The XML element name.
+{1} - The runtime lookup key.
+{2} - The first target.
+{3} - The conflicting target.</comment>
+  </data>
+  <data name="XA4325_NativeAotObjectRequired" xml:space="preserve">
+    <value>NativeAOT JNI retention requires an existing post-ILC NativeAotObjectFile; '{0}' was not found.</value>
+    <comment>The following are literal names and should not be translated: NativeAOT, JNI, ILC, NativeAotObjectFile.
+{0} - The path of the missing ILC native object, or an empty string if none was supplied.</comment>
+  </data>
+  <data name="XA4325_NativeAotObjectReadFailure" xml:space="preserve">
+    <value>The NativeAOT retention object '{0}' could not be read: {1}</value>
+    <comment>The following is a literal name and should not be translated: NativeAOT.
+{0} - The path of the ILC native object.
+{1} - The exception message.</comment>
+  </data>
+  <data name="XA4325_NativeAotModeRequired" xml:space="preserve">
+    <value>NativeAotObjectFile requires NativeAot=true.</value>
+    <comment>The following are literal names and should not be translated: NativeAotObjectFile, NativeAot=true.</comment>
+  </data>
+  <data name="XA4325_NativeAotObjectFormat" xml:space="preserve">
+    <value>Expected a 32-bit or 64-bit little-endian relocatable NativeAOT ELF object.</value>
+    <comment>The following are literal names and should not be translated: NativeAOT, ELF.</comment>
+  </data>
+  <data name="XA4325_NativeAotInvalidSection" xml:space="preserve">
+    <value>The NativeAOT ELF object contains an invalid section extent.</value>
+    <comment>The following are literal names and should not be translated: NativeAOT, ELF.</comment>
+  </data>
+  <data name="XA4325_NativeAotTruncatedSection" xml:space="preserve">
+    <value>The NativeAOT ELF object contains truncated section data.</value>
+    <comment>The following are literal names and should not be translated: NativeAOT, ELF.</comment>
+  </data>
+  <data name="XA4325_NativeAotMissingSections" xml:space="preserve">
+    <value>The NativeAOT object must contain allocated __managedcode and initialized data sections.</value>
+    <comment>The following are literal names and should not be translated: NativeAOT, __managedcode.</comment>
+  </data>
+  <data name="XA4326" xml:space="preserve">
+    <value>The R8 JNI remapping data is incomplete. {0}</value>
+    <comment>The following are literal names and should not be translated: R8, JNI.
+{0} - A sentence describing the specific omission.</comment>
+  </data>
+  <data name="XA4326_ConflictingEntry" xml:space="preserve">
+    <value>The '{0}' entry for '{1}' was not emitted: another JNI remapping input already maps it to '{2}', which conflicts with '{3}'.</value>
+    <comment>The following is a literal name and should not be translated: JNI.
+{0} - The XML element name.
+{1} - The source lookup key.
+{2} - The existing target.
+{3} - The generated target.</comment>
+  </data>
+  <data name="XA4326_UnsupportedSignature" xml:space="preserve">
+    <value>The entry for '{0}' was not emitted: its signature '{1}' could not be converted to a JNI descriptor.</value>
+    <comment>The following is a literal name and should not be translated: JNI.
+{0} - The member the entry describes.
+{1} - The Java signature which could not be converted.</comment>
   </data>
   <data name="XA4327" xml:space="preserve">
     <value>Could not extract Java type map keys from '{0}': {1}</value>

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

@@ -64,7 +64,7 @@ public override bool RunTask ()
 
 		void GenerateEmpty ()
 		{
-			Generate (new JniRemappingAssemblyGenerator (Log));
+			Generate (new JniRemappingNativeCodeGenerator (Log));
 		}
 
 		void Generate (string remappingXmlFilePath)
@@ -86,10 +86,10 @@ void Generate (string remappingXmlFilePath)
 				}
 			}
 
-			Generate (new JniRemappingAssemblyGenerator (Log, typeReplacements, reverseTypeReplacements, methodReplacements, fieldReplacements));
+			Generate (new JniRemappingNativeCodeGenerator (Log, typeReplacements, reverseTypeReplacements, methodReplacements, fieldReplacements));
 		}
 
-		void Generate (JniRemappingAssemblyGenerator jniRemappingComposer)
+		void Generate (JniRemappingNativeCodeGenerator jniRemappingComposer)
 		{
 			LLVMIR.LlvmIrModule module =  jniRemappingComposer.Construct ();
 
@@ -146,7 +146,6 @@ void ReadXml (XmlReader reader, List<JniRemappingTypeReplacement> typeReplacemen
 					if (!haveAllAttributes) {
 						continue;
 					}
-
 					reverseTypeReplacements.Add (new JniRemappingTypeReplacement (from, to));
 				} else if (MonoAndroidHelper.StringEquals ("replace-method", reader.LocalName)) {
 					haveAllAttributes &= GetRequiredAttribute ("source-type", out string sourceType);
@@ -164,10 +163,10 @@ void ReadXml (XmlReader reader, List<JniRemappingTypeReplacement> typeReplacemen
 						continue;
 					}
 
-					string sourceMethodSignature = reader.GetAttribute ("source-method-signature");
+					string sourceMethodSignature = reader.GetAttribute ("source-method-signature") ?? "";
 					// Optional: inputs which predate it (for example the Intune/MAM mapping) keep
 					// the source signature on the target method.
-					string targetMethodSignature = reader.GetAttribute ("target-method-signature");
+					string? targetMethodSignature = reader.GetAttribute ("target-method-signature");
 					methodReplacements.Add (
 						new JniRemappingMethodReplacement (
 							sourceType, sourceMethodName, sourceMethodSignature,
@@ -179,13 +178,12 @@ void ReadXml (XmlReader reader, List<JniRemappingTypeReplacement> typeReplacemen
 					haveAllAttributes &= GetRequiredAttribute ("source-field-name", out string sourceFieldName);
 					haveAllAttributes &= GetRequiredAttribute ("target-type", out string targetType);
 					haveAllAttributes &= GetRequiredAttribute ("target-field-name", out string targetFieldName);
-
 					if (!haveAllAttributes) {
 						continue;
 					}
 
-					string sourceFieldSignature = reader.GetAttribute ("source-field-signature");
-					string targetFieldSignature = reader.GetAttribute ("target-field-signature");
+					string sourceFieldSignature = reader.GetAttribute ("source-field-signature") ?? "";
+					string? targetFieldSignature = reader.GetAttribute ("target-field-signature");
 					fieldReplacements.Add (
 						new JniRemappingFieldReplacement (
 							sourceType, sourceFieldName, sourceFieldSignature,