refactor: remove unauthorized spec

benchmark/Benchmark.cs

@@ -126,10 +126,10 @@ public int DeserializeAllProperties()
             ReadOnlySpan<int> integers = view.Integers;
             ReadOnlySpan<long> longs = view.Longs;
             ReadOnlySpan<PackedBenchmarkValue> packedValues = view.PackedValues;
-            NestedPayloadView nested = view.Nested;
-            int nestedVersion = nested.Version;
-            ReadOnlySpan<char> nestedLabel = nested.Label;
-            PackedBenchmarkValueView nestedSummary = nested.Summary;
+            NestedPayloadView? nested = view.Nested;
+            int nestedVersion = nested?.Version ?? -1;
+            ReadOnlySpan<char> nestedLabel = (nested ?? new()).Label;  // Nullable<ReadOnlySpan<char>> is invalid
+            PackedBenchmarkValueView nestedSummary = nested?.Summary ?? new();
             NestedStructPayloadView nestedStruct = view.NestedStruct;
             int nestedStructCode = nestedStruct.Code;
             long nestedStructAmount = nestedStruct.Amount;

src/FieldGenerationModel.cs

@@ -33,6 +33,8 @@ internal FieldGenerationModel(
 
     internal int ElementByteCount { get; }
 
+    internal int BlittableByteOffset { get; set; }
+
     internal ITypeSymbol? ArrayElementType { get; }
 
     internal INamedTypeSymbol? NestedSerializableType { get; }

src/ZeroSerializerGenerator.cs

@@ -328,6 +328,7 @@
         }
 
         // Roslyn's member order is the wire declaration order; never infer a different order from file paths or spans.
+        int blittableByteOffset = 0;
         foreach (ISymbol declaredMember in serializableType.GetMembers())
         {
             // Only public getter properties define the wire contract; fields, setters, and indexers must never leak into it.
@@ -362,7 +363,9 @@
                 continue;
             }
 
+            propertyModel.BlittableByteOffset = blittableByteOffset;
             generationModel.Fields.Add(propertyModel);
+            blittableByteOffset += propertyModel.ElementByteCount;
         }
 
         return generationModel;
@@ -1194,14 +1197,28 @@
             propertyType = field.Symbol.Type.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
         }
 
-        sourceBuilder.AppendLine($"{propertyAccessibility} {propertyType} {EscapeIdentifier(field.Symbol.Name)}");
+        var propertyReturnType
+            = field.Kind is FieldSerializationKind.BlittableStruct or FieldSerializationKind.Nested
+            ? (field.NullableUnderlyingType is not null || field.Symbol.Type.TypeKind is TypeKind.Class)
+                ? GetQualifiedViewName(field.NestedSerializableType) + "?"
+                : GetQualifiedViewName(field.NestedSerializableType)
+            : propertyType;
+        sourceBuilder.AppendLine($"{propertyAccessibility} {propertyReturnType} {EscapeIdentifier(field.Symbol.Name)}");
         sourceBuilder.OpenBlock();
         sourceBuilder.AppendLine("get");
         sourceBuilder.OpenBlock();
         if (containingModel.IsBlittableStruct)
         {
-            sourceBuilder.AppendLine($"{containingModel.QualifiedSourceTypeName} blittableSourceValue = MemoryMarshal.Read<{containingModel.QualifiedSourceTypeName}>(serializedMemory.Span);");
-            sourceBuilder.AppendLine($"return blittableSourceValue.{EscapeIdentifier(field.Symbol.Name)};");
+            if (field.Kind == FieldSerializationKind.BlittableStruct
+                && field.NestedSerializableType is not null)
+            {
+                sourceBuilder.AppendLine($"return new {GetQualifiedViewName(field.NestedSerializableType)}(serializedMemory.Slice({field.BlittableByteOffset}, {field.ElementByteCount}));");
+            }
+            else
+            {
+                sourceBuilder.AppendLine($"{containingModel.QualifiedSourceTypeName} blittableSourceValue = MemoryMarshal.Read<{containingModel.QualifiedSourceTypeName}>(serializedMemory.Span);");
+                sourceBuilder.AppendLine($"return blittableSourceValue.{EscapeIdentifier(field.Symbol.Name)};");
+            }
             sourceBuilder.CloseBlock();
             sourceBuilder.CloseBlock();
             return;
@@ -1214,14 +1231,8 @@
             // Null is represented entirely by the offset table; no property payload marker is read.
             sourceBuilder.AppendLine("if (fieldDataOffset == 0)");
             sourceBuilder.OpenBlock();
-            if (field.NullableUnderlyingType is not null && field.Kind != FieldSerializationKind.Nested)
-            {
-                sourceBuilder.AppendLine("return null;");
-            }
-            else
-            {
-                sourceBuilder.AppendLine("return default;");
-            }
+            // Always use 'default' instead of 'null' for reference types.
+            sourceBuilder.AppendLine("return default;");
             sourceBuilder.CloseBlock();
         }
 
@@ -1268,8 +1279,8 @@
         }
 
         sourceBuilder.CloseBlock();
         sourceBuilder.CloseBlock();
     }
 
     private static void EmitViewCollectionHeader(
         GeneratedSourceBuilder sourceBuilder,

tests-unity/UnityCompatibility.cs

@@ -119,11 +119,11 @@
     && variableView.OptionalState == PacketState.Ready
     && variableView.OptionalPosition!.Value.X == 30
     && variableView.MissingOptionalPosition is null
-    && variableView.Child.Identifier == 99
+    && variableView.Child?.Identifier == 99
     && variableView.StructChild.Identifier == 100
     && variableView.StructChild.Name.SequenceEqual("struct".AsSpan())
-    && variableView.OptionalStructChild.Identifier == 101
-    && variableView.OptionalStructChild.Name.SequenceEqual("optional struct".AsSpan())
+    && variableView.OptionalStructChild?.Identifier == 101
+    && variableView.OptionalStructChild?.Name.SequenceEqual("optional struct".AsSpan()) == true
     && variableView.FloatValues.Length == 3
     && variableView.FloatValues[1] == 2.5f
     && variableView.DoubleValues.Length == 3
@@ -267,7 +267,7 @@
     public int? OptionalValue { get; init; }
 
     public int? MissingOptionalValue { get; init; }
 
     public PacketState? OptionalState { get; init; }
 
     public PackedPosition? OptionalPosition { get; init; }

tests/SerializationTests.cs

@@ -246,12 +246,12 @@ public void VariableDataRoundTrip()
 
         int expectedRequiredByteLength = -(24 + (4 * IntPtr.Size));
         TestAssert.Equal(expectedRequiredByteLength, VariableRecordView.RequiredByteLength, nameof(VariableRecordView.RequiredByteLength));
-        TestAssert.Equal(source.Text, view.Text.ToString(), nameof(view.Text));
-        TestAssert.SequenceEqual<int>(source.Values, view.Values, nameof(view.Values));
-        TestAssert.Equal(source.OptionalNumber, view.OptionalNumber, nameof(view.OptionalNumber));
-        TestAssert.Equal(source.Child.Identifier, view.Child.Identifier, nameof(view.Child.Identifier));
-        TestAssert.Equal(source.Child.State, view.Child.State, nameof(view.Child.State));
-        TestAssert.Equal(source.Tail, view.Tail, nameof(view.Tail));
+        TestAssert.Equal(source.Text, view.Text.ToString(), nameof(source.Text));
+        TestAssert.SequenceEqual<int>(source.Values, view.Values, nameof(source.Values));
+        TestAssert.Equal(source.OptionalNumber, view.OptionalNumber, nameof(source.OptionalNumber));
+        TestAssert.Equal(source.Child.Identifier, view.Child?.Identifier ?? -1, nameof(source.Child.Identifier));
+        TestAssert.Equal(source.Child.State, view.Child?.State ?? ByteState.None, nameof(source.Child.State));
+        TestAssert.Equal(source.Tail, view.Tail, nameof(source.Tail));
         int textFieldOffset = BinaryPrimitives.ReadInt32LittleEndian(buffer.AsSpan(0, 4));
         int valuesFieldOffset = BinaryPrimitives.ReadInt32LittleEndian(buffer.AsSpan(4, 4));
         int optionalNumberFieldOffset = BinaryPrimitives.ReadInt32LittleEndian(buffer.AsSpan(8, 4));
@@ -284,8 +284,8 @@ public void VariableViewOnlyRequiresCorrectSerializedStart()
         TestAssert.Equal(source.Text, view.Text.ToString(), nameof(view.Text));
         TestAssert.SequenceEqual<int>(source.Values, view.Values, nameof(view.Values));
         TestAssert.Equal(source.OptionalNumber, view.OptionalNumber, nameof(view.OptionalNumber));
-        TestAssert.Equal(source.Child.Identifier, view.Child.Identifier, nameof(view.Child.Identifier));
-        TestAssert.Equal(source.Child.State, view.Child.State, nameof(view.Child.State));
+        TestAssert.Equal(source.Child.Identifier, view.Child?.Identifier ?? -1, nameof(FixedClassView.Identifier));
+        TestAssert.Equal(source.Child.State, view.Child?.State ?? ByteState.None, nameof(FixedClassView.State));
         TestAssert.Equal(source.Tail, view.Tail, nameof(view.Tail));
 
         ReadOnlyMemory<byte> borrowedSerializedMemory = view;
@@ -521,9 +521,9 @@ public void EveryTruncatedSerializedBufferThrowsStandardBoundsExceptionWhenRead(
                 _ = view.Text.Length;
                 _ = view.Values.Length;
                 _ = view.OptionalNumber;
-                FixedClassView childView = view.Child;
-                _ = childView.Identifier;
-                _ = childView.State;
+                FixedClassView? childView = view.Child;
+                _ = childView?.Identifier;
+                _ = childView?.State;
                 _ = view.Tail;
             },
             nameof(VariableRecord));
@@ -777,7 +777,7 @@ public void NestedTypesReturnViewsTest()
         // 2. Assert that nested non-blittable type returns view
         PropertyInfo? childProperty = typeof(VariableRecordView).GetProperty(nameof(VariableRecordView.Child));
         Assert.NotNull(childProperty);
-        Assert.Equal(typeof(FixedClassView), childProperty!.PropertyType);
+        Assert.Equal(typeof(FixedClassView?), childProperty!.PropertyType);
     }
 
     public void StrictBlittableStructTests()