Added support for nested classes

src/MemoryPack.Generator/DiagnosticDescriptors.cs

@@ -17,14 +17,6 @@ internal static class DiagnosticDescriptors
         defaultSeverity: DiagnosticSeverity.Error,
         isEnabledByDefault: true);
 
-    public static readonly DiagnosticDescriptor NestedNotAllow = new(
-        id: "MEMPACK002",
-        title: "MemoryPackable object must not be nested type",
-        messageFormat: "The MemoryPackable object '{0}' must be not nested type",
-        category: Category,
-        defaultSeverity: DiagnosticSeverity.Error,
-        isEnabledByDefault: true);
-
     public static readonly DiagnosticDescriptor AbstractMustUnion = new(
         id: "MEMPACK003",
         title: "abstract/interface type of MemoryPackable object must annotate with Union",
@@ -340,4 +332,12 @@ internal static class DiagnosticDescriptors
         category: Category,
         defaultSeverity: DiagnosticSeverity.Error,
         isEnabledByDefault: true);
+
+    public static readonly DiagnosticDescriptor NestedContainingTypesMustBePartial = new(
+        id: "MEMPACK042",
+        title: "Nested MemoryPackable object's containing type(s) must be partial",
+        messageFormat: "The MemoryPackable object '{0}' containing type(s) must be partial",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true);
 }

src/MemoryPack.Generator/MemoryPackGenerator.Emitter.cs

@@ -25,10 +25,9 @@ static void Generate(TypeDeclarationSyntax syntax, Compilation compilation, stri
             return;
         }
 
-        // nested is not allowed
-        if (IsNested(syntax))
+        if (IsNested(syntax) && !IsNestedContainingTypesPartial(syntax))
         {
-            context.ReportDiagnostic(Diagnostic.Create(DiagnosticDescriptors.NestedNotAllow, syntax.Identifier.GetLocation(), typeSymbol.Name));
+            context.ReportDiagnostic(Diagnostic.Create(DiagnosticDescriptors.NestedContainingTypesMustBePartial, syntax.Identifier.GetLocation(), typeSymbol.Name));
             return;
         }
 
@@ -157,6 +156,21 @@ static bool IsPartial(TypeDeclarationSyntax typeDeclaration)
         return typeDeclaration.Modifiers.Any(m => m.IsKind(SyntaxKind.PartialKeyword));
     }
 
+    static bool IsNestedContainingTypesPartial(TypeDeclarationSyntax typeDeclaration)
+    {
+        if (typeDeclaration.Parent is TypeDeclarationSyntax parentTypeDeclaration)
+        {
+            if (!IsPartial(parentTypeDeclaration))
+                return false;
+
+            return IsNestedContainingTypesPartial(parentTypeDeclaration);
+        }
+        else
+        {
+            return true;
+        }
+    }
+
     static bool IsNested(TypeDeclarationSyntax typeDeclaration)
     {
         return typeDeclaration.Parent is TypeDeclarationSyntax;
@@ -296,6 +310,21 @@ public void Emit(StringBuilder writer, IGeneratorContext context)
             (false, false) => "class",
         };
 
+        var containingTypeDeclarations = new List<string>();
+        var containingType = Symbol.ContainingType;
+        while (containingType is not null)
+        {
+            containingTypeDeclarations.Add((containingType.IsRecord, containingType.IsValueType) switch
+            {
+                (true, true) => $"partial record struct {containingType.Name}",
+                (true, false) => $"partial record {containingType.Name}",
+                (false, true) => $"partial struct {containingType.Name}",
+                (false, false) => $"partial class {containingType.Name}",
+            });
+            containingType = containingType.ContainingType;
+        }
+        containingTypeDeclarations.Reverse();
+
         var nullable = IsValueType ? "" : "?";
 
         string staticRegisterFormatterMethod, staticMemoryPackableMethod, scopedRef, constraint, registerBody, registerT;
@@ -345,6 +374,12 @@ public void Emit(StringBuilder writer, IGeneratorContext context)
             ? "Serialize(ref MemoryPackWriter"
             : "Serialize<TBufferWriter>(ref MemoryPackWriter<TBufferWriter>";
 
+        foreach (var declaration in containingTypeDeclarations)
+        {
+            writer.AppendLine(declaration);
+            writer.AppendLine("{");
+        }
+
         writer.AppendLine($$"""
 partial {{classOrStructOrRecord}} {{TypeName}} : IMemoryPackable<{{TypeName}}>{{fixedSizeInterface}}
 {
@@ -420,6 +455,10 @@ public override void Deserialize(ref MemoryPackReader reader, {{scopedRef}} {{Ty
             writer.AppendLine(code);
         }
 
+        for(int i = 0; i < containingTypeDeclarations.Count; ++i)
+        {
+            writer.AppendLine("}");
+        }
     }
 
     private string EmitDeserializeBody()

tests/MemoryPack.Tests/GeneratorDiagnosticsTest.cs

@@ -43,22 +43,6 @@ public class Hoge
 """);
     }
 
-    [Fact]
-    public void MEMPACK002_NestedNotAllow()
-    {
-        Compile(2, """
-using MemoryPack;
-
-public partial class Hoge
-{
-    [MemoryPackable]
-    public partial class Huga
-    {
-    }
-}
-""");
-    }
-
     [Fact]
     public void MEMPACK003_AbstractMustUnion()
     {
@@ -703,6 +687,23 @@ public partial struct Tester
 }
 """);
     }
+
+    [Fact]
+    public void MEMPACK042_NestedContainingTypesMustBePartial()
+    {
+        Compile(42, """
+                    using MemoryPack;
+
+                    public struct NestedContainer
+                    {
+                        [MemoryPackable]
+                        public partial struct NestedStruct
+                        {
+                            public int I1 { get; init; }
+                        }
+                    }
+                    """);
+    }
 }
 
 #endif

tests/MemoryPack.Tests/GeneratorTest.cs

@@ -50,6 +50,13 @@ public void Standard()
         VerifyEquivalent(new GlobalNamespaceType() { MyProperty = 10000 });
     }
 
+    [Fact]
+    public void Nested()
+    {
+        VerifyEquivalent(new NestedContainer.StandardTypeNested() { One = 9999 });
+        VerifyEquivalent(new DoublyNestedContainer.DoublyNestedContainerInner.StandardTypeDoublyNested() { One = 9999 });
+    }
+
     [Fact]
     public void Null()
     {

tests/MemoryPack.Tests/Models/StandardType.cs

@@ -62,6 +62,27 @@ public StandardStruct()
         }
     }
 
+    public partial class NestedContainer
+    {
+        [MemoryPackable]
+        public partial class StandardTypeNested
+        {
+            public int One { get; set; }
+        }
+    }
+
+    public partial class DoublyNestedContainer
+    {
+        public partial class DoublyNestedContainerInner
+        {
+            [MemoryPackable]
+            public partial class StandardTypeDoublyNested
+            {
+                public int One { get; set; }
+            }
+        }
+    }
+
 
     [MemoryPackable]
     public partial class WithArray