Handle shared FieldRVA names conservatively

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: simonrozsival

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/JniRemapping/JniAssemblyRewriterTests.cs

@@ -699,7 +699,6 @@ public void RewritesUtf8FieldRvaJniNamesAndSignatures ()
 
 			FieldDefinitionHandle nameField = fixture.AddUtf8Field ("onClick");
 			FieldDefinitionHandle signatureField = fixture.AddUtf8Field ("(Lacme/orig/Callback;)V");
-			FieldDefinitionHandle classNameField = fixture.AddUtf8Field ("acme/orig/Callback");
 			FieldDefinitionHandle longNameField = fixture.AddUtf8Field ("run");
 
 			int fieldStart = fixture.NextFieldRid;
@@ -755,7 +754,6 @@ public void RewritesUtf8FieldRvaJniNamesAndSignatures ()
 
 			Assert.AreEqual ("a", ReadUtf8Field (peReader, reader, nameField), "The method name is renamed using the owning proxy's JNI class.");
 			Assert.AreEqual ("(La/b/Cb;)V", ReadUtf8Field (peReader, reader, signatureField));
-			Assert.AreEqual ("a/b/Cb", ReadUtf8Field (peReader, reader, classNameField), "An unreferenced datum that is a known class name is still renamed.");
 			Assert.AreEqual ("aMuchLongerObfuscatedName", ReadUtf8Field (peReader, reader, longNameField), "A longer datum is relocated into a wider __utf8_N slot.");
 
 			// Growing a datum appends exactly one new sized type; no existing token moves.
@@ -799,6 +797,62 @@ public void FailsWhenASharedUtf8DatumNeedsTwoDifferentNames ()
 			StringAssert.Contains ("shared", exception.Message.ToLowerInvariant ());
 		}
 
+		[Test]
+		public void FailsWhenASharedUtf8DatumMustRemainUnmappedForOneProxy ()
+		{
+			var fixture = new JniFixtureBuilder ();
+
+			FieldDefinitionHandle shared = fixture.AddUtf8Field ("go");
+			FieldDefinitionHandle signature = fixture.AddUtf8Field ("()V");
+
+			AddProxy (fixture, "acme/orig/P1", shared, signature);
+			AddProxy (fixture, "acme/orig/P2", shared, signature);
+
+			var exception = Assert.Throws<JniRewriteException> (() => Rewrite (fixture.Serialize (), Mapping (
+				"acme.orig.P1 -> a.b.P1:\n" +
+				"    void go() -> z\n" +
+				"acme.orig.P2 -> a.b.P2:\n")));
+			StringAssert.Contains ("shared", exception.Message.ToLowerInvariant ());
+			StringAssert.Contains ("original value", exception.Message);
+			StringAssert.Contains ("'go'", exception.Message);
+			StringAssert.Contains ("'z'", exception.Message);
+		}
+
+		[Test]
+		public void FailsWhenASharedUtf8DatumHasAnUnresolvedOwner ()
+		{
+			var fixture = new JniFixtureBuilder ();
+
+			FieldDefinitionHandle shared = fixture.AddUtf8Field ("go");
+			FieldDefinitionHandle signature = fixture.AddUtf8Field ("()V");
+
+			AddProxy (fixture, "acme/orig/P1", shared, signature);
+			AddRegistrationTypeWithoutJniOwner (fixture, shared, signature);
+
+			var exception = Assert.Throws<JniRewriteException> (() => Rewrite (fixture.Serialize (), Mapping (
+				"acme.orig.P1 -> a.b.P1:\n" +
+				"    void go() -> z\n")));
+			StringAssert.Contains ("shared", exception.Message.ToLowerInvariant ());
+			StringAssert.Contains ("original value", exception.Message);
+		}
+
+		[Test]
+		public void PreservesUnreferencedUtf8DatumThatMatchesAMappedClass ()
+		{
+			var fixture = new JniFixtureBuilder ();
+			FieldDefinitionHandle field = fixture.AddUtf8Field ("acme/orig/Callback");
+			byte [] image = fixture.Serialize ();
+			R8Mapping mapping = Mapping ("acme.orig.Callback -> a.b.Cb:\n");
+
+			JniRewriteResult result = Rewrite (image, mapping);
+
+			Assert.AreSame (image, result.Image);
+			Assert.AreEqual (0, result.ReplacementCount);
+			CollectionAssert.IsEmpty (mapping.AccessedEntries);
+			using var peReader = new PEReader (ImmutableArray.Create (result.Image));
+			Assert.AreEqual ("acme/orig/Callback", ReadUtf8Field (peReader, peReader.GetMetadataReader (), field));
+		}
+
 		static void AddProxy (JniFixtureBuilder fixture, string jniName, FieldDefinitionHandle nameField, FieldDefinitionHandle signatureField)
 		{
 			int fieldStart = fixture.NextFieldRid;
@@ -825,6 +879,24 @@ static void AddProxy (JniFixtureBuilder fixture, string jniName, FieldDefinition
 				TypeAttributes.Public | TypeAttributes.Sealed | TypeAttributes.Class, fixture.JavaPeerProxyReference);
 		}
 
+		static void AddRegistrationTypeWithoutJniOwner (JniFixtureBuilder fixture, FieldDefinitionHandle nameField, FieldDefinitionHandle signatureField)
+		{
+			int fieldStart = fixture.NextFieldRid;
+			int methodStart = fixture.NextMethodRid;
+
+			fixture.AddVoidMethod ("RegisterNatives", fixture.EmitBody (encoder => {
+				encoder.OpCode (ILOpCode.Ldsflda);
+				encoder.Token (nameField);
+				encoder.OpCode (ILOpCode.Ldsflda);
+				encoder.Token (signatureField);
+				encoder.OpCode (ILOpCode.Pop);
+				encoder.OpCode (ILOpCode.Pop);
+				encoder.OpCode (ILOpCode.Ret);
+			}));
+
+			fixture.AddType ("Acme.Orig", "UnknownOwner", fieldStart, methodStart);
+		}
+
 		[Test]
 		public void SharedLoadedStringGetsOwnerSpecificReplacements ()
 		{

src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/JniRewritePlanner.cs

@@ -980,8 +980,9 @@ void PlanUtf8FieldData (JniRewritePlan plan)
 					}
 					if (resolved != null && resolved != candidate) {
 						throw new JniRewriteException (
-							$"The mapped UTF-8 JNI datum '{value}' is shared by more than one Java class, but the mapping renames it to both " +
-							$"'{resolved}' and '{candidate}'. Splitting a shared '{FieldRvaTable.Utf8FieldNamePrefix}' field would move metadata tokens, which this rewriter does not do.");
+							$"The UTF-8 JNI datum '{value}' is shared by uses that require incompatible values '{resolved}' and '{candidate}'. " +
+							$"At least one use may require the original value because its owning Java class or member mapping could not be resolved. " +
+							$"Splitting a shared '{FieldRvaTable.Utf8FieldNamePrefix}' field would move metadata tokens, which this rewriter does not do.");
 					}
 					resolved ??= candidate;
 				}
@@ -1002,20 +1003,21 @@ IEnumerable<Utf8Use> GetUses (FieldDefinitionHandle field)
 
 		string? ComputeNewUtf8Value (string value, Utf8Use use)
 		{
-			if (use.Role == Utf8Role.MethodName && use.OwnerJniName != null && use.PairedSignature != null) {
-				JniDescriptorText.MethodDescriptorToJavaTypes (use.PairedSignature, out var javaParams, out string javaReturnType);
-				string mappingName = R8Mapping.JniMemberNameToMappingName (value);
-				return mapping.TryMapMethod (use.OwnerJniName, mappingName, javaParams, javaReturnType, out string renamed) ? renamed : null;
+			if (use.Role == Utf8Role.MethodName) {
+				if (use.OwnerJniName != null && use.PairedSignature != null) {
+					JniDescriptorText.MethodDescriptorToJavaTypes (use.PairedSignature, out var javaParams, out string javaReturnType);
+					string mappingName = R8Mapping.JniMemberNameToMappingName (value);
+					if (mapping.TryMapMethod (use.OwnerJniName, mappingName, javaParams, javaReturnType, out string renamed)) {
+						return renamed;
+					}
+				}
+				return value;
 			}
 
 			if (JniDescriptorText.IsValidMethodDescriptor (value) || JniDescriptorText.IsValidFieldDescriptor (value)) {
 				return JniDescriptorText.TryRewriteDescriptor (value, renameClass, out string rewritten) ? rewritten : null;
 			}
 
-			if (use.Role == Utf8Role.Unknown && mapping.TryMapClass (value, out string renamedClass)) {
-				return renamedClass;
-			}
-
 			return null;
 		}