Add GetTypeInfo<T>() and TryGetTypeInfo<T>() to JsonSerializerOptions

[Copilot]

Description

Implements the approved API from API review to add generic overloads of GetTypeInfo that return JsonTypeInfo<T> directly, eliminating the need for manual downcasting.

namespaceSystem.Text.Json;publicpartialclassJsonSerializerOptions{publicJsonTypeInfo<T>GetTypeInfo<T>();publicboolTryGetTypeInfo<T>([NotNullWhen(true)]outJsonTypeInfo<T>?typeInfo);}

Changes

• JsonSerializerOptions.Caching.cs: Added generic GetTypeInfo<T>() and TryGetTypeInfo<T>() instance methods that delegate to the non-generic versions
• System.Text.Json.cs (ref): Updated public API surface
• OptionsTests.cs: Added 6 tests covering mutable/immutable options, type resolution, and equivalence with non-generic versions
• Production code updates: Replaced usages of the cast pattern (JsonTypeInfo<T>)options.GetTypeInfo(typeof(T)) with the new generic options.GetTypeInfo<T>():
  • JsonNode.cs - JsonNode.ToNode<T>()
  • JsonValue.cs - JsonValue.Create<T>()
• Test file updates: Replaced usages across 5 test files:
  • PolymorphicTests.cs
  • CustomConverterTests.Object.cs
  • OptionsTests.cs
  • JsonValueTests.cs
  • JsonSerializerContextTests.cs

Usage

// Beforevarinfo=(JsonTypeInfo<string>)options.GetTypeInfo(typeof(string));// Aftervarinfo=options.GetTypeInfo<string>();

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[API Proposal]: JsonSerializerOptions.GetTypeInfo</issue_title>
<issue_description>### Background and motivation

There's already a GetTypeInfo method that takes a System.Type, but a really common case is to downcast to the generic version. This API makes it simple to perform the same operation without introducing potential errors.

API Proposal

namespaceSystem.Text.Json;publicstaticclassJsonSerializerOptionsExtensions{publicstaticSystem.Text.Json.Serialization.Metadata.JsonTypeInfo<T>GetTypeInfo<T>(thisJsonSerializerOptionsoptions){thrownull;}}

API Usage

See, for example,

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonNode.cs

Line 391 in 8b08265

varjsonTypeInfo=(JsonTypeInfo<T>)JsonSerializerOptions.Default.GetTypeInfo(typeof(T));

// Old usevarinfo=(JsonTypeInfo<string>)options.GetTypeInfo(typeof(string));// New usevarinfo=options.GetTypeInfo<string>();

Alternative Designs

No response

Risks

No response</issue_description>

<agent_instructions>Implement and test the approved API surface area commented by bartonjs. Tests should be added to existing files.</agent_instructions>

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

@eiriktsarpalis Why not just make it an instance method on the class directly? @agocke Avoids taking any dependencies on internals, which shouldn't be needed. @eiriktsarpalis Not sure I follow, what internals do you have in mind? @agocke Nothing specific. I don’t feel strongly about it, I just thought that convenience helpers are best placed as extensions, not regular members. The primary reason to use a regular member is to access private fields. If there is no access to private fields, extension members avoid introducing such a dependency. It’s also easier to move from extension member to regular member than vice versa. @eiriktsarpalis Sounds good, I'm sure it will be debated extensively during API review. @bartonjs I'm pretty sure it's going to be an instance member 😄 @bartonjs [Video](https://www.youtube.com/watch?v=BeoDUMLNAFw&t=1h14m21s)

• The method should be an instance method instead of an extension method.
• Let's go ahead and approve the Try at the same time.

namespaceSystem.Text.Json;publicpartialclassJsonSerializerOptions{publicJsonTypeInfo<T>GetTypeInfo<T>();publicboolTryGetTypeInfo<T>([NotNullWhen(true)]outJsonTypeInfo<T>?typeInfo);}
```</body></comment_new></comments>

• Fixes[API Proposal]: JsonSerializerOptions.GetTypeInfo<T> #118468

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[stephentoub]

@copilot are there any places throughout the repo where non-generic {Try}GetTypeInfo methods are being used that the new generic ones should be used instead? Please search for and replace such uses.

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[Copilot]

@copilot are there any places throughout the repo where non-generic {Try}GetTypeInfo methods are being used that the new generic ones should be used instead? Please search for and replace such uses.

Updated 15 usages across 6 test files to use the new generic methods in 64eab66:

• PolymorphicTests.cs
• CustomConverterTests.Object.cs
• OptionsTests.cs
• JsonValueTests.cs
• JsonSerializerContextTests.cs
• JsonSerializerWrapper.cs

No production code usages were found (only test code was using the cast pattern).

[stephentoub]

No production code usages were found

@copilot, what about places like:

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonNode.cs

Line 391 in 4fa6991

varjsonTypeInfo=(JsonTypeInfo<T>)JsonSerializerOptions.Default.GetTypeInfo(typeof(T));

runtime/src/libraries/System.Net.Http.Json/src/System/Net/Http/Json/HttpClientJsonExtensions.Get.AsyncEnumerable.cs

Line 138 in 4fa6991

varjsonTypeInfo=(JsonTypeInfo<TValue>)JsonHelpers.GetJsonTypeInfo(typeof(TValue),options);

runtime/src/libraries/System.Net.Http.Json/src/System/Net/Http/Json/HttpContentJsonExtensions.AsyncEnumerable.cs

Line 89 in 4fa6991

varjsonTypeInfo=(JsonTypeInfo<TValue>)JsonHelpers.GetJsonTypeInfo(typeof(TValue),options);

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonValue.cs

Line 67 in 4fa6991

varjsonTypeInfo=(JsonTypeInfo<T>)JsonSerializerOptions.Default.GetTypeInfo(typeof(T));

etc.?

[Copilot]

No production code usages were found

@copilot, what about places like:
...

Updated the production code in b40934d:

• JsonNode.cs - JsonNode.ToNode<T>()
• JsonValue.cs - JsonValue.Create<T>()
• JsonHelpers.cs - Added generic GetJsonTypeInfo<T>() helper
• HttpClientJsonExtensions.Get.AsyncEnumerable.cs
• HttpContentJsonExtensions.AsyncEnumerable.cs

[agocke]

@stephentoub thanks! I planned to do this myself, but hadn’t gotten around to it yet