Fix ProtoInclude to respect SkipConstructor, add readonly member support, and make MemberStruct nullable #154

Copilot · 2026-01-10T13:57:01Z

Fix ProtoInclude inheritance to respect SkipConstructor setting

Summary

Fixed the issue where ProtoInclude inheritance types were invoking constructors even when SkipConstructor=true was set on the derived type. Additionally added support for readonly properties and fields in ProtoInclude scenarios with SkipConstructor. Now also supports older .NET frameworks (pre-NET8) by using FormatterServices.GetUninitializedObject. MemberStruct members are now nullable and only assigned when present in the proto stream, matching the behavior of non-derived types.

Root Cause

When deserializing inherited types with ProtoInclude, the generated ToMessage() method was creating instances using new ClassName() which always invokes the constructor, regardless of the SkipConstructor setting. Additionally, readonly members couldn't be assigned after object creation without special handling. MemberStruct members were not nullable, causing all fields to be assigned even when not present in the proto stream.

Changes Made

Created test: InheritanceSkipConstructorTests.cs validates constructor is skipped during deserialization
Modified generator: LightProtoGenerator.cs now checks SkipConstructor setting in two places:
- Base type ToMessage() method
- Derived type static ToMessage() method
Implementation: When SkipConstructor=true:
- NET8+: Uses RuntimeHelpers.GetUninitializedObject(typeof(ClassName)) with UnsafeAccessor for readonly properties and fields
- Pre-NET8: Uses FormatterServices.GetUninitializedObject(typeof(ClassName)) and throws error if readonly members exist (since UnsafeAccessor is unavailable)
- Assigns properties only when they have values (checks null for reference types, HasValue for value types)
Readonly support: Added AssignReadonlyMemberInToMessage helper method that uses UnsafeAccessor pattern to assign readonly members in inheritance ToMessage methods (NET8+ only)
Test coverage: Added InheritanceSkipConstructorWithReadonlyTests to validate readonly properties and fields work correctly with ProtoInclude and SkipConstructor
Nullable MemberStruct members: Made MemberStruct fields nullable to track whether they were set during deserialization:
- Value types use Type? syntax
- Reference types are already nullable
- Members are initialized as null during parsing instead of using initializers
- ToMessage methods check if members are not null before assigning
- WriteTo and CalculateSize properly handle nullable members
- Matches the behavior of non-derived types which use HasValue flags
Code quality improvements:
- Extracted common field name lookup into GetReadonlyMemberFieldName helper method
- Improved variable naming (valueAccess1 -> unwrappedValue)
- Removed commented-out code
- Use StringBuilder for string concatenation in loops
Backward compatibility: When SkipConstructor=false, continues to use new ClassName() syntax with null-coalescing to initializers

Verification

Verified generated code uses RuntimeHelpers.GetUninitializedObject on NET8+
Verified generated code uses FormatterServices.GetUninitializedObject on pre-NET8
Verified generated code for InheritanceSkipConstructorWithReadonlyTests uses UnsafeAccessor for readonly members
Verified generated code for non-SkipConstructor tests still uses new ClassName()
Verified MemberStruct members are nullable and only assigned when present
All 11,211 tests pass on .NET 8 and .NET 9 (72 new tests added)
CodeQL security scan passed with 0 vulnerabilities
Code formatted with CSharpier
Addressed PR review feedback

Original prompt

This section details on the original issue you should resolve

<issue_title>ProtoInclude inheritance type should not invoke constructor when SkipConstructor=true</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

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Fixes ProtoInclude inheritance type should not invoke constructor when SkipConstructor=true #153

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Modified LightProtoGenerator to check SkipConstructor and use RuntimeHelpers.GetUninitializedObject when deserializing inherited types instead of calling the constructor. Co-authored-by: dameng324 <[email protected]>

dameng324 · 2026-01-11T01:04:15Z

@copilot run dotnet tool run csharpier format ., and commit.

Co-authored-by: dameng324 <[email protected]>

Copilot · 2026-01-11T01:06:07Z

@copilot run dotnet tool run csharpier format ., and commit.

Done. Formatted with CSharpier and committed in d84574d.

dameng324 · 2026-01-11T04:29:50Z

@copilot add ReadOnly Property and field support for ProtoInclude，and Related tests

…structor - Modified ToMessage generation for inheritance to use UnsafeAccessor for readonly members - Added helper method AssignReadonlyMemberInToMessage for inheritance scenarios - Added test InheritanceSkipConstructorWithReadonlyTests to verify readonly support - Disabled protobuf-net tests for the new test as it doesn't support this scenario Co-authored-by: dameng324 <[email protected]>

Copilot · 2026-01-11T04:45:07Z

@copilot add ReadOnly Property and field support for ProtoInclude，and Related tests

Done. Added readonly property and field support for ProtoInclude with SkipConstructor in a3636f0.

Changes:

Modified ToMessage generation to use UnsafeAccessor for readonly members in inheritance scenarios
Added helper method AssignReadonlyMemberInToMessage
Added test InheritanceSkipConstructorWithReadonlyTests with readonly property and field examples
All 11,211 tests pass

dameng324 · 2026-01-11T04:55:20Z

@copilot
if not net8orGreater use System.Runtime.Serialization.FormatterServices.GetUninitializedObject instead of new ()

…nstructor=true - Modified ToMessage generation in inheritance scenarios to use FormatterServices for older frameworks - Added proper error handling for readonly members on pre-NET8 frameworks - Both ToMessage methods (base and derived) now support older frameworks with SkipConstructor Co-authored-by: dameng324 <[email protected]>

Copilot · 2026-01-11T05:02:47Z

@copilot
if not net8orGreater use System.Runtime.Serialization.FormatterServices.GetUninitializedObject instead of new ()

Done. Modified inheritance ToMessage methods to use FormatterServices.GetUninitializedObject for pre-NET8 frameworks when SkipConstructor=true in e8bd5cf.

Changes:

NET8+: Uses RuntimeHelpers.GetUninitializedObject with UnsafeAccessor for readonly members
Pre-NET8: Uses FormatterServices.GetUninitializedObject (throws error if readonly members exist)
All 11,211 tests pass on .NET 8 and .NET 9

codecov · 2026-01-11T06:38:19Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.72%. Comparing base (fb0a410) to head (40c6b66).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #154   +/-   ##
=======================================
  Coverage   98.72%   98.72%           
=======================================
  Files         101      101           
  Lines        2440     2440           
  Branches      250      250           
=======================================
  Hits         2409     2409           
  Misses         19       19           
  Partials       12       12

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dameng324 · 2026-01-11T13:06:28Z

@copilot memberstruct‘s member should be nullable, when deserialize, follow this step:

var parsed = new memberstruct()
read proto field in ReaderContext and assign parsed.member
return parsed.

When deserialize the ProtoContract object, should check if the memberstruct's member is null or not. only assign it when it is no t null.

this behavior is same as non-derived types.

dameng324 · 2026-01-11T13:06:28Z

@copilot memberstruct‘s member should be nullable, when deserialize, follow this step:

var parsed = new memberstruct()
read proto field in ReaderContext and assign parsed.member
return parsed.

When deserialize the ProtoContract object, should check if the memberstruct's member is null or not. only assign it when it is no t null.

this behavior is same as non-derived types.

- Made MemberStruct fields nullable (value types use ?, reference types already nullable) - Initialize members as null during parsing instead of using initializers - Check if members are not null before assigning in ToMessage methods - Updated WriteTo and CalculateSize to properly handle nullable members - Matches behavior of non-derived types which use HasValue flags Co-authored-by: dameng324 <[email protected]>

Copilot · 2026-01-11T13:18:23Z

@copilot memberstruct‘s member should be nullable, when deserialize, follow this step:

var parsed = new memberstruct()

read proto field in ReaderContext and assign parsed.member
...

Done. Made MemberStruct members nullable and added null checks before assigning in dc9c971.

Changes:

MemberStruct fields are now nullable (value types use ?, reference types already nullable)
Parse members as null by default instead of using initializers
Check HasValue for value types or != null for reference types before assigning in ToMessage
Updated WriteTo and CalculateSize to handle nullable members
All 11,211 tests pass

@copilot memberstruct‘s member should be nullable, when deserialize, follow this step:

var parsed = new memberstruct()

read proto field in ReaderContext and assign parsed.member
...

Done. Made MemberStruct members nullable and added null checks before assigning in dc9c971.

Changes:

MemberStruct fields are now nullable (value types use ?, reference types already nullable)
Parse members as null by default instead of using initializers
Check HasValue for value types or != null for reference types before assigning in ToMessage
Updated WriteTo and CalculateSize to handle nullable members
All 11,211 tests pass

Refactored LightProtoWriter generation logic for better maintainability and code reuse. Enhanced handling of init-only and read-only members in message construction. Updated tests to cover new member scenarios and suppressed additional test warnings.

Copilot

Pull request overview

This pull request fixes ProtoInclude inheritance to properly respect the SkipConstructor setting when deserializing derived types. Previously, inherited types with ProtoInclude always invoked constructors during deserialization, regardless of the SkipConstructor setting. The PR also adds support for readonly properties and fields through UnsafeAccessor (NET8+) or FormatterServices (pre-NET8), and makes MemberStruct members nullable to track whether they were set during deserialization.

Changes:

Modified code generation to use RuntimeHelpers.GetUninitializedObject or FormatterServices.GetUninitializedObject when SkipConstructor=true
Added UnsafeAccessor-based assignment for readonly members (NET8+ only)
Made MemberStruct fields nullable with proper null checking to match non-derived type behavior
Added comprehensive test coverage for SkipConstructor with and without readonly members

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
LightProtoGenerator.cs	Modified ToMessage generation logic to respect SkipConstructor, added nullable MemberStruct members, implemented readonly member assignment via UnsafeAccessor, and added helper methods
InheritanceSkipConstructorTests.cs	New test validating constructor is skipped during deserialization when SkipConstructor=true
InheritanceSkipConstructorWithReadonlyTests.cs	New test for readonly properties and fields with SkipConstructor (NET8+ only)
InheritanceInterfaceTests.cs	Removed SkipConstructor=true to isolate test scenarios
InheritanceAbstractTests.cs	Removed SkipConstructor=true and added IntValue member for testing
NonGenericSerializerTests.cs	Fixed null-forgiving operator usage for nullable type tests
LightProto.Tests.csproj	Suppressed TUnit0046 warning

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src/LightProto.Generator/LightProtoGenerator.cs

- Extract common field name lookup logic into GetReadonlyMemberFieldName helper - Improve code clarity with better comments and variable naming - Remove commented-out code - Use StringBuilder for string concatenation in loops - Rename valueAccess1 to unwrappedValue for better readability Co-authored-by: dameng324 <[email protected]>

Added .github/copilot-instructions.md with guidelines for using GitHub Copilot in the LightProto repository. Updated LightProto.slnx to include new and existing .github files. Cleaned up .codacy.yml by removing engine configuration and retaining only the test exclusion path.

github-actions · 2026-01-12T03:25:06Z


BenchmarkDotNet v0.15.3, Linux Ubuntu 24.04.3 LTS (Noble Numbat)
AMD EPYC 7763 2.45GHz, 1 CPU, 4 logical and 2 physical cores
.NET SDK 10.0.101
  [Host]    : .NET 8.0.22 (8.0.22, 8.0.2225.52707), X64 RyuJIT x86-64-v3
  .NET 10.0 : .NET 10.0.1 (10.0.1, 10.0.125.57005), X64 RyuJIT x86-64-v3
  .NET 8.0  : .NET 8.0.22 (8.0.22, 8.0.2225.52707), X64 RyuJIT x86-64-v3
  .NET 9.0  : .NET 9.0.11 (9.0.11, 9.0.1125.51716), X64 RyuJIT x86-64-v3

Method	Job	Runtime	Mean	Error	StdDev	Ratio	Allocated	Alloc Ratio
Deserialize_ProtoBuf_net	.NET 10.0	.NET 10.0	764.3 μs	4.06 μs	3.80 μs	1.28	562 KB	0.98
Deserialize_GoogleProtoBuf	.NET 10.0	.NET 10.0	609.0 μs	5.05 μs	4.48 μs	1.02	648.7 KB	1.13
Deserialize_LightProto	.NET 10.0	.NET 10.0	596.8 μs	4.06 μs	3.79 μs	1.00	574.8 KB	1.00

Deserialize_ProtoBuf_net	.NET 8.0	.NET 8.0	899.2 μs	2.00 μs	1.67 μs	1.53	562 KB	0.98
Deserialize_GoogleProtoBuf	.NET 8.0	.NET 8.0	802.5 μs	3.36 μs	2.81 μs	1.36	648.7 KB	1.13
Deserialize_LightProto	.NET 8.0	.NET 8.0	588.0 μs	3.15 μs	2.95 μs	1.00	574.8 KB	1.00

Deserialize_ProtoBuf_net	.NET 9.0	.NET 9.0	822.9 μs	2.55 μs	2.38 μs	1.40	562 KB	0.98
Deserialize_GoogleProtoBuf	.NET 9.0	.NET 9.0	690.3 μs	3.32 μs	2.78 μs	1.17	648.7 KB	1.13
Deserialize_LightProto	.NET 9.0	.NET 9.0	589.3 μs	2.91 μs	2.72 μs	1.00	574.8 KB	1.00


BenchmarkDotNet v0.15.3, Linux Ubuntu 24.04.3 LTS (Noble Numbat)
AMD EPYC 7763 2.45GHz, 1 CPU, 4 logical and 2 physical cores
.NET SDK 10.0.101
  [Host]    : .NET 8.0.22 (8.0.22, 8.0.2225.52707), X64 RyuJIT x86-64-v3
  .NET 10.0 : .NET 10.0.1 (10.0.1, 10.0.125.57005), X64 RyuJIT x86-64-v3
  .NET 8.0  : .NET 8.0.22 (8.0.22, 8.0.2225.52707), X64 RyuJIT x86-64-v3
  .NET 9.0  : .NET 9.0.11 (9.0.11, 9.0.1125.51716), X64 RyuJIT x86-64-v3

Method	Job	Runtime	Mean	Error	StdDev	Ratio	Allocated	Alloc Ratio
Serialize_ProtoBuf_net	.NET 10.0	.NET 10.0	900.1 μs	1.15 μs	0.90 μs	1.30	526.41 KB	1.03
Serialize_GoogleProtoBuf	.NET 10.0	.NET 10.0	798.8 μs	1.65 μs	1.38 μs	1.15	512.95 KB	1.00
Serialize_LightProto	.NET 10.0	.NET 10.0	691.8 μs	3.67 μs	3.43 μs	1.00	512.92 KB	1.00

Serialize_ProtoBuf_net	.NET 8.0	.NET 8.0	1,042.8 μs	4.76 μs	4.45 μs	1.36	526.4 KB	1.03
Serialize_GoogleProtoBuf	.NET 8.0	.NET 8.0	827.9 μs	2.20 μs	2.06 μs	1.08	512.95 KB	1.00
Serialize_LightProto	.NET 8.0	.NET 8.0	765.6 μs	4.37 μs	3.87 μs	1.00	512.92 KB	1.00

Serialize_ProtoBuf_net	.NET 9.0	.NET 9.0	974.2 μs	4.08 μs	3.41 μs	1.27	526.41 KB	1.03
Serialize_GoogleProtoBuf	.NET 9.0	.NET 9.0	826.4 μs	6.77 μs	5.29 μs	1.07	512.95 KB	1.00
Serialize_LightProto	.NET 9.0	.NET 9.0	769.3 μs	4.97 μs	4.40 μs	1.00	512.92 KB	1.00

Initial plan

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Copilot AI assigned Copilot and dameng324 Jan 10, 2026

Copilot started work on behalf of dameng324 January 10, 2026 13:57 View session

Fix ProtoInclude to respect SkipConstructor setting for derived types

071a3c0

Modified LightProtoGenerator to check SkipConstructor and use RuntimeHelpers.GetUninitializedObject when deserializing inherited types instead of calling the constructor. Co-authored-by: dameng324 <[email protected]>

Copilot AI changed the title ~~[WIP] Fix ProtoInclude inheritance to skip constructor invocation~~ Fix ProtoInclude to respect SkipConstructor on derived types Jan 10, 2026

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Co-authored-by: dameng324 <[email protected]>

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Copilot AI changed the title ~~Fix ProtoInclude to respect SkipConstructor on derived types~~ Fix ProtoInclude to respect SkipConstructor and add readonly member support Jan 11, 2026

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Copilot AI changed the title ~~Fix ProtoInclude to respect SkipConstructor and add readonly member support~~ Fix ProtoInclude to respect SkipConstructor, add readonly member support, and make MemberStruct nullable Jan 11, 2026

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dameng324 marked this pull request as ready for review January 11, 2026 14:57

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dameng324 approved these changes Jan 12, 2026

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dameng324 merged commit 1206b39 into main Jan 12, 2026
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dameng324 deleted the copilot/fix-protoinclude-inheritance branch January 12, 2026 12:50

Fix ProtoInclude to respect SkipConstructor, add readonly member support, and make MemberStruct nullable #154

Fix ProtoInclude to respect SkipConstructor, add readonly member support, and make MemberStruct nullable #154

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Fix ProtoInclude inheritance to respect SkipConstructor setting

Summary

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