Fix #1329: AssertionFailedException: Should not insert using declaration for namespace that is missing from the superset: System.Windows.Markup

ICSharpCode.Decompiler/CSharp/RequiredNamespaceCollector.cs

@@ -86,13 +86,15 @@ namespace ICSharpCode.Decompiler.CSharp
 						CollectNamespacesForTypeReference(param.Type, namespaces);
 					}
 					HandleTypeParameters(method.TypeParameters, namespaces);
-					if (!method.MetadataToken.IsNil && method.HasBody) {
+					if (!method.MetadataToken.IsNil) {
 						if (mappingInfo == null)
 							mappingInfo = CSharpDecompiler.GetCodeMappingInfo(entity.ParentModule.PEFile, entity.MetadataToken);
 						var reader = module.PEFile.Reader;
 						var parts = mappingInfo.GetMethodParts((MethodDefinitionHandle)method.MetadataToken).ToList();
 						foreach (var part in parts) {
+							HandleOverrides(part.GetMethodImplementations(module.metadata), module, namespaces);
 							var methodDef = module.metadata.GetMethodDefinition(part);
+							if (method.HasBody) {
 								MethodBodyBlock body;
 								try {
 									body = reader.GetMethodBody(methodDef.RelativeVirtualAddress);
@@ -102,6 +104,7 @@ namespace ICSharpCode.Decompiler.CSharp
 								CollectNamespacesFromMethodBody(body, module, namespaces);
 							}
 						}
+					}
 					break;
 				case IProperty property:
 					HandleAttributes(property.GetAttributes(), namespaces);
@@ -116,6 +119,16 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
+		static void HandleOverrides(ImmutableArray<MethodImplementationHandle> immutableArray, MetadataModule module, HashSet<string> namespaces)
+		{
+			foreach (var h in immutableArray) {
+				var methodImpl = module.metadata.GetMethodImplementation(h);
+				CollectNamespacesForTypeReference(module.ResolveType(methodImpl.Type, genericContext), namespaces);
+				CollectNamespacesForMemberReference(module.ResolveMethod(methodImpl.MethodBody, genericContext), module, namespaces);
+				CollectNamespacesForMemberReference(module.ResolveMethod(methodImpl.MethodDeclaration, genericContext), module, namespaces);
+			}
+		}
+
 		static void CollectNamespacesForTypeReference(IType type, HashSet<string> namespaces)
 		{
 			switch (type) {