Fix bugs found by newly ported tests.

src/libraries/System.Private.DataContractSerialization/src/Resources/Strings.resx

@@ -1381,7 +1381,7 @@
     <value>Simple type restriction must specify a base type.</value>
   </data>
   <data name="SimpleTypeUnionNotSupported" xml:space="preserve">
-    <value>=Simple types with &lt;union&gt; content are not supported.</value>
+    <value>Simple types with &lt;union&gt; content are not supported.</value>
   </data>
   <data name="SpecifiedTypeNotFoundInSchema" xml:space="preserve">
     <value>Invalid type specified. Type with name '{0}' not found in schema with namespace '{1}'.</value>

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/ClassDataContract.cs

@@ -1361,7 +1361,7 @@ internal override DataContract BindGenericParameters(DataContract[] paramContrac
         }
 
         [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
-        internal override bool Equals(object? other, HashSet<DataContractPairKey> checkedContracts)
+        internal override bool Equals(object? other, HashSet<DataContractPairKey>? checkedContracts)
         {
             if (IsEqualOrChecked(other, checkedContracts))
                 return true;

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/CollectionDataContract.cs

@@ -1491,7 +1491,7 @@ internal bool RequiresMemberAccessForWrite(SecurityException? securityException)
         }
 
         [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
-        internal override bool Equals(object? other, HashSet<DataContractPairKey> checkedContracts)
+        internal override bool Equals(object? other, HashSet<DataContractPairKey>? checkedContracts)
         {
             if (IsEqualOrChecked(other, checkedContracts))
                 return true;

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/DataContract.cs

@@ -2057,7 +2057,7 @@ public sealed override bool Equals(object? obj)
         }
 
         [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
-        internal virtual bool Equals(object? other, HashSet<DataContractPairKey> checkedContracts)
+        internal virtual bool Equals(object? other, HashSet<DataContractPairKey>? checkedContracts)
         {
             if (other is DataContract dataContract)
             {
@@ -2066,18 +2066,21 @@ internal virtual bool Equals(object? other, HashSet<DataContractPairKey> checked
             return false;
         }
 
-        internal bool IsEqualOrChecked(object? other, HashSet<DataContractPairKey> checkedContracts)
+        internal bool IsEqualOrChecked(object? other, HashSet<DataContractPairKey>? checkedContracts)
         {
             if (other == null)
                 return false;
 
             if ((object)this == other)
                 return true;
 
-            DataContractPairKey contractPairKey = new DataContractPairKey(this, other);
-            if (checkedContracts.Contains(contractPairKey))
-                return true;
-            checkedContracts.Add(contractPairKey);
+            if (checkedContracts != null)
+            {
+                DataContractPairKey contractPairKey = new DataContractPairKey(this, other);
+                if (checkedContracts.Contains(contractPairKey))
+                    return true;
+                checkedContracts.Add(contractPairKey);
+            }
 
             return false;
         }

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/DataContractSet.cs

@@ -92,8 +92,7 @@ internal void Add(XmlQualifiedName name, DataContract dataContract)
         {
             if (dataContract.IsBuiltInDataContract)
                 return;
-            if (dataContract is DataContract dataContractInternal)
-                InternalAdd(name, dataContractInternal);
+            InternalAdd(name, dataContract);
         }
 
         [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
@@ -167,16 +166,19 @@ private void AddClassDataContract(ClassDataContract classDataContract)
         [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
         private void AddCollectionDataContract(CollectionDataContract collectionDataContract)
         {
-            if (collectionDataContract.IsDictionary)
+            if (collectionDataContract.UnderlyingType != Globals.TypeOfSchemaDefinedType)
             {
-                ClassDataContract keyValueContract = (collectionDataContract.ItemContract as ClassDataContract)!;
-                AddClassDataContract(keyValueContract);
-            }
-            else
-            {
-                DataContract itemContract = GetItemTypeDataContract(collectionDataContract);
-                if (itemContract != null)
-                    Add(itemContract.XmlName, itemContract);
+                if (collectionDataContract.IsDictionary)
+                {
+                    ClassDataContract keyValueContract = (collectionDataContract.ItemContract as ClassDataContract)!;
+                    AddClassDataContract(keyValueContract);
+                }
+                else
+                {
+                    DataContract itemContract = GetItemTypeDataContract(collectionDataContract);
+                    if (itemContract != null)
+                        Add(itemContract.XmlName, itemContract);
+                }
             }
             AddKnownDataContracts(collectionDataContract.KnownDataContracts);
         }

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/DataMember.cs

@@ -298,7 +298,7 @@ internal DataMember BindGenericParameters(DataContract[] paramContracts, Diction
         }
 
         [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
-        internal bool Equals(object? other, HashSet<DataContractPairKey> checkedContracts)
+        internal bool Equals(object? other, HashSet<DataContractPairKey>? checkedContracts)
         {
             if (this == other)
                 return true;

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/EnumDataContract.cs

@@ -401,6 +401,43 @@ internal long GetEnumValueFromString(string value)
             }
         }
 
+        [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
+        internal override bool Equals(object? other, HashSet<DataContractPairKey>? checkedContracts)
+        {
+            if (IsEqualOrChecked(other, checkedContracts))
+                return true;
+
+            if (base.Equals(other, null))
+            {
+                if (other is EnumDataContract enumContract)
+                {
+                    if (Members.Count != enumContract.Members.Count || Values?.Count != enumContract.Values?.Count)
+                        return false;
+                    string[] memberNames1 = new string[Members.Count], memberNames2 = new string[Members.Count];
+                    for (int i = 0; i < Members.Count; i++)
+                    {
+                        memberNames1[i] = Members[i].Name;
+                        memberNames2[i] = enumContract.Members[i].Name;
+                    }
+                    Array.Sort(memberNames1);
+                    Array.Sort(memberNames2);
+                    for (int i = 0; i < Members.Count; i++)
+                    {
+                        if (memberNames1[i] != memberNames2[i])
+                            return false;
+                    }
+
+                    return (IsFlags == enumContract.IsFlags);
+                }
+            }
+            return false;
+        }
+
+        public override int GetHashCode()
+        {
+            return base.GetHashCode();
+        }
+
         [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
         internal override void WriteXmlValue(XmlWriterDelegator xmlWriter, object obj, XmlObjectSerializerWriteContext? context)
         {

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/Globals.cs

@@ -320,6 +320,12 @@ internal static Type TypeOfHashtable
         internal static Type TypeOfSchemaDefinedType =>
             s_typeOfSchemaDefinedType ??= typeof(SchemaDefinedType);
 
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.NonPublicFields)]
+        private static Type? s_typeOfSchemaDefinedEnum;
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.NonPublicFields)]
+        internal static Type TypeOfSchemaDefinedEnum =>
+            s_typeOfSchemaDefinedEnum ??= typeof(SchemaDefinedEnum);
+
         private static MemberInfo? s_schemaMemberInfoPlaceholder;
         internal static MemberInfo SchemaMemberInfoPlaceholder =>
             s_schemaMemberInfoPlaceholder ??= TypeOfSchemaDefinedType.GetField("_xmlName", BindingFlags.NonPublic | BindingFlags.Instance)!;

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/PrimitiveDataContract.cs

@@ -119,7 +119,7 @@ protected static bool TryReadNullAtTopLevel(XmlReaderDelegator reader)
         }
 
         [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
-        internal override bool Equals(object? other, HashSet<DataContractPairKey> checkedContracts)
+        internal override bool Equals(object? other, HashSet<DataContractPairKey>? checkedContracts)
         {
             if (other is PrimitiveDataContract)
             {

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/SchemaHelper.cs

@@ -37,6 +37,8 @@ public SchemaDefinedType(XmlQualifiedName xmlName)
         }
     }
 
+    internal enum SchemaDefinedEnum { SchemaDefinedEnumValue };
+
     internal static class SchemaHelper
     {
         internal static bool NamespacesEqual(string? ns1, string? ns2)

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/SchemaImporter.cs

@@ -935,15 +935,13 @@ private void ImportClassMember(XmlSchemaElement element, ClassDataContract dataC
         {
             XmlQualifiedName typeName = dataContract.XmlName;
 
-            Debug.Assert(element.Name != null);
-
             if (element.MinOccurs > 1)
                 ThrowTypeCannotBeImportedException(typeName.Name, typeName.Namespace, SR.Format(SR.ElementMinOccursMustBe, element.Name));
             if (element.MaxOccurs != 1)
                 ThrowTypeCannotBeImportedException(typeName.Name, typeName.Namespace, SR.Format(SR.ElementMaxOccursMustBe, element.Name));
 
             DataContract? memberTypeContract = null;
-            string memberName = element.Name;
+            string? memberName = element.Name;
             bool memberIsRequired = (element.MinOccurs > 0);
             bool memberIsNullable = element.IsNillable;
             bool memberEmitDefaultValue;
@@ -987,6 +985,7 @@ private void ImportClassMember(XmlSchemaElement element, ClassDataContract dataC
                 memberEmitDefaultValue = emitDefaultValueFromAnnotation != null ? emitDefaultValueFromAnnotation.Value : Globals.DefaultEmitDefaultValue;
 
             Debug.Assert(dataContract.Members != null); // This method is only called from ImportClass() after that method has initialized the Members collection.
+            Debug.Assert(memberName != null);   // At this point, elements without a name should have been handled.
 
             int prevMemberIndex = dataContract.Members.Count - 1;
             if (prevMemberIndex >= 0)
@@ -1179,7 +1178,7 @@ private static bool IsDictionary(XmlQualifiedName typeName, XmlSchemaAnnotation?
         [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
         private EnumDataContract ImportEnum(XmlQualifiedName typeName, XmlSchemaSimpleTypeRestriction restriction, bool isFlags, XmlSchemaAnnotation? annotation)
         {
-            EnumDataContract dataContract = new EnumDataContract(Globals.TypeOfSchemaDefinedType);
+            EnumDataContract dataContract = new EnumDataContract(Globals.TypeOfSchemaDefinedEnum);
             dataContract.XmlName = typeName;
             dataContract.BaseContractName = ImportActualType(annotation, SchemaExporter.DefaultEnumBaseTypeName, typeName);
             dataContract.IsFlags = isFlags;

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/XmlDataContract.cs

@@ -379,7 +379,7 @@ internal IXmlSerializable ReflectionCreateXmlSerializable(Type type)
         }
 
         [RequiresUnreferencedCode(DataContract.SerializerTrimmerWarning)]
-        internal override bool Equals(object? other, HashSet<DataContractPairKey> checkedContracts)
+        internal override bool Equals(object? other, HashSet<DataContractPairKey>? checkedContracts)
         {
             if (IsEqualOrChecked(other, checkedContracts))
                 return true;