Document breaking change for Type.MakeGenericSignatureType argument validation in .NET 10 Preview 3

[Copilot]

Fixes #48902

This PR adds documentation for a breaking change in .NET 10 Preview 3 where Type.MakeGenericSignatureType now validates that the genericTypeDefinition argument is actually a generic type definition.

Changes

Previous Behavior

The Type.MakeGenericSignatureType API accepted any type for the genericTypeDefinition argument, including non-generic types, which resulted in non-sensical behavior.

New Behavior

Starting in .NET 10, the API requires the genericTypeDefinition argument to be a generic type definition and throws an ArgumentException if the validation fails.

Recommended Action

Developers should check if a type is a generic type definition before calling the API:

// Before
Type instantiatedType = Type.MakeGenericSignatureType(originalType, instantiation);

// After
Type instantiatedType = originalType.IsGenericTypeDefinition 
    ? Type.MakeGenericSignatureType(originalType, instantiation) 
    : originalType;

Files Changed

• Created new breaking change document: docs/core/compatibility/reflection/10/makegeneric-signaturetype-validation.md
• Updated docs/core/compatibility/10.0.md to add entry in Core .NET libraries section
• Updated docs/core/compatibility/toc.yml to add new Reflection section under .NET 10

This is a behavioral breaking change that affects the System.Type.MakeGenericSignatureType API.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Breaking change] Type.MakeGenericSignatureType argument validation</issue_title>
<issue_description>### Description

Starting in .NET 10 Preview 3, Type.MakeGenericSignatureType API validates that the genericTypeDefinition argument is in fact a generic type definition.

Version

.NET 10 Preview 3

Previous behavior

Type.MakeGenericSignatureType accepted any type for the genericTypeDefinition argument.

New behavior

Type.MakeGenericSignatureType requires genericTypeDefinition argument to be a generic type definition and throws ArgumentException otherwise.

Type of breaking change

• Behavioral change: Existing binaries might behave differently at runtime.

Reason for change

The type created by Type.MakeGenericSignatureType had non-sensical behavior when the genericTypeDefinition argument was not a generic type definition.

Recommended action

Avoid calling Type.MakeGenericSignatureType for types that are not generic type definitions. For example:

// Before
Type instantiatedType = Type.MakeGenericSignatureType(originalType, instantiation);

// After
Type instantiatedType = originalType.IsGenericTypeDefinition ? Type.MakeGenericSignatureType(originalType, instantiation) : originalType;

Affected APIs

• System.Type.MakeGenericSignatureType

---

Associated WorkItem - 496357</issue_description>

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

Fixes #48902

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Internal previews

📄 File	🔗 Preview link
docs/core/compatibility/10.0.md	docs/core/compatibility/10.0
docs/core/compatibility/reflection/10/makegeneric-signaturetype-validation.md	docs/core/compatibility/reflection/10/makegeneric-signaturetype-validation
docs/core/compatibility/toc.yml	docs/core/compatibility/toc

[Copilot]

Pull Request Overview

This PR documents a breaking change in .NET 10 Preview 3 where Type.MakeGenericSignatureType now validates that the genericTypeDefinition argument is actually a generic type definition, throwing an ArgumentException if validation fails.

• Creates comprehensive documentation for the breaking change with proper API references and code examples
• Updates the compatibility documentation index to include the new breaking change entry
• Adds a new Reflection section to the .NET 10 compatibility table of contents

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
docs/core/compatibility/toc.yml	Adds new Reflection section under .NET 10 with entry for the breaking change
docs/core/compatibility/reflection/10/makegeneric-signaturetype-validation.md	Creates the main breaking change documentation with detailed explanation and examples
docs/core/compatibility/10.0.md	Adds entry to the Core .NET libraries section referencing the new breaking change document

[jkotas]

Thanks