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Add ZEROS009 diagnostic for StructLayout attribute on non-struct types #88

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Add ZEROS009 diagnostic for StructLayout attribute on non-struct types #88

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2c381a8
Add ZEROS009 warning diagnostic for StructLayout on non-struct types
google-labs-jules[bot] Aug 20, 2026
915f779
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sator-imaging Aug 20, 2026
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36 changes: 31 additions & 5 deletions src/ZeroSerializerGenerator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,14 @@ public sealed class ZeroSerializerGenerator : ISourceGenerator
DiagnosticSeverity.Error,
isEnabledByDefault: true);

private static readonly DiagnosticDescriptor InvalidClassStructLayoutAttribute = new(
"ZEROS009",
"StructLayout attribute on class",
"StructLayout attribute on class '{0}' has no effect",
SerializerName,
DiagnosticSeverity.Warning,
isEnabledByDefault: true);

public void Initialize(GeneratorInitializationContext initializationContext)
{
// Unity is pinned to Roslyn 3.8, so discovery must stay on the classic syntax-receiver API.
Expand Down Expand Up @@ -316,6 +324,20 @@ private static TypeGenerationModel CreateGenerationModel(
return generationModel;
}

if (serializableType.TypeKind != TypeKind.Struct)
{
var structLayoutAttr = GetStructLayoutAttribute(serializableType);
if (structLayoutAttr is not null)
{
Location? location = structLayoutAttr.ApplicationSyntaxReference?.GetSyntax().GetLocation()
?? GetTypeIdentifierLocation(serializableType);
executionContext.ReportDiagnostic(Diagnostic.Create(
InvalidClassStructLayoutAttribute,
location,
serializableType.Name));
}
}

if (serializableType.TypeKind == TypeKind.Struct && !isBlittableStruct)
{
var packOneAttr = GetSequentialPackOneAttribute(serializableType);
Expand Down Expand Up @@ -631,10 +653,9 @@ private static bool TryGetBlittableStructByteCount(INamedTypeSymbol candidateTyp
out byteCount);
}

private static AttributeData? GetSequentialPackOneAttribute(INamedTypeSymbol structType)
private static AttributeData? GetStructLayoutAttribute(INamedTypeSymbol typeSymbol)
{
AttributeData? structLayoutAttribute = null;
foreach (AttributeData candidateAttribute in structType.GetAttributes())
foreach (AttributeData candidateAttribute in typeSymbol.GetAttributes())
{
if (candidateAttribute.AttributeClass is INamedTypeSymbol
{
Expand All @@ -653,10 +674,15 @@ private static bool TryGetBlittableStructByteCount(INamedTypeSymbol candidateTyp
}
})
{
structLayoutAttribute = candidateAttribute;
break;
return candidateAttribute;
}
}
return null;
}

private static AttributeData? GetSequentialPackOneAttribute(INamedTypeSymbol structType)
{
AttributeData? structLayoutAttribute = GetStructLayoutAttribute(structType);
if (structLayoutAttribute is null
|| structLayoutAttribute.ConstructorArguments.Length != 1
|| structLayoutAttribute.ConstructorArguments[0].Value is not int layoutKind
Expand Down
61 changes: 61 additions & 0 deletions tests/Diagnostics/DiagnosticTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,67 @@ await CSharpSourceGeneratorVerifier<ZeroSerializerGenerator>.VerifySourceGenerat
);
}

[Fact]
public async Task ZEROS009_Violation_ClassWithStructLayout()
{
string source = @"
using System.Runtime.InteropServices;
using ZeroSerializer;

[{|#0:StructLayout(LayoutKind.Sequential, Pack = 1)|}]
[ZeroSerializer]
public class MyClassWithStructLayout
{
public int Value { get; set; }
}
";

await CSharpSourceGeneratorVerifier<ZeroSerializerGenerator>.VerifySourceGeneratorAsync(
source,
new DiagnosticResult("ZEROS009", DiagnosticSeverity.Warning)
.WithLocation(0)
.WithMessage("StructLayout attribute on class 'MyClassWithStructLayout' has no effect")
);
}

[Fact]
public async Task ZEROS009_Compliant_StructWithAttributes()
{
string source = @"
using System.Runtime.InteropServices;
using ZeroSerializer;

[StructLayout(LayoutKind.Sequential, Pack = 1)]
[ZeroSerializer]
public struct MyStructWithAttributes
{
public int Value { get; set; }
}
";

await CSharpSourceGeneratorVerifier<ZeroSerializerGenerator>.VerifySourceGeneratorAsync(
source
);
}

[Fact]
public async Task ZEROS009_Compliant_ClassWithoutZeroSerializer()
{
string source = @"
using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential, Pack = 1)]
public class MyClassWithoutZeroSerializer
{
public int Value { get; set; }
}
";

await CSharpSourceGeneratorVerifier<ZeroSerializerGenerator>.VerifySourceGeneratorAsync(
source
);
}

[Fact]
public async Task ZEROS002_Violation_NonBlittableStructWithLayout()
{
Expand Down
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