Add IReadOnlySet support to System.Text.Json

[sander1095]

This pull request adds support for serializing and deserializing IReadOnlySet<T> collections in the System.Text.Json library. The changes include updates to the codebase to recognize IReadOnlySet<T> as a collection type, introduce a dedicated converter for it, and provide comprehensive tests to ensure correct behavior. This enhancement aligns the library's handling of IReadOnlySet<T> with other collection interfaces like ISet<T> and ICollection<T>.

Core serialization/deserialization support

• Added a new converter IReadOnlySetOfTConverter<TCollection, TElement> to handle serialization and deserialization of IReadOnlySet<T>, including logic to deserialize as HashSet<T> when appropriate. (src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IReadOnlySetOfTConverter.cs)
• Updated the converter factory and metadata services to recognize and use the new converter for types assignable to IReadOnlySet<T>. (src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableConverterFactory.cs, src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonMetadataServices.Collections.cs) [1] [2]
• Registered the new converter in the project file for compilation. (src/libraries/System.Text.Json/src/System.Text.Json.csproj)

Type recognition and source generator integration

• Enhanced type symbol helpers and collection type enumeration to include IReadOnlySet<T>, enabling source generator and parser logic to identify and process this collection type. (src/libraries/System.Text.Json/gen/Helpers/KnownTypeSymbols.cs, src/libraries/System.Text.Json/gen/Model/CollectionType.cs, src/libraries/System.Text.Json/gen/JsonSourceGenerator.Parser.cs, src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs) [1] [2] [3] [4]
• Added a metadata service API for source generator scenarios: CreateIReadOnlySetInfo<TCollection, TElement>. (src/libraries/System.Text.Json/ref/System.Text.Json.cs, src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonMetadataServices.Collections.cs) [1] [2]

Test coverage

• Added comprehensive read and write tests for IReadOnlySet<T>, covering primitive types, nested sets, arrays, and nullable scenarios. (src/libraries/System.Text.Json/tests/Common/CollectionTests/CollectionTests.Generic.Read.cs, src/libraries/System.Text.Json/tests/Common/CollectionTests/CollectionTests.Generic.Write.cs) [1] [2] [3] [4] [5]

Minor fixes

• Fixed a typo in an exception helper method name (JsonConverterFactoryReturnsJsonConverterFactorty → JsonConverterFactoryReturnsJsonConverterFactory). (src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterFactory.cs, src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs) [1] [2]This pull request adds support for serializing and deserializing IReadOnlySet<T> collections in System.Text.Json for .NET versions greater or equal to 5.0. The changes are carefully scoped to only apply when targeting compatible frameworks, and include updates to the source generator, converter infrastructure, and test coverage.

Support for IReadOnlySet collections:

• Added a new converter, IReadOnlySetOfTConverter, to handle serialization and deserialization of IReadOnlySet<T> types, falling back to HashSet<T> for deserialization. (src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IReadOnlySetOfTConverter.cs)
• Updated the source generator and metadata services to recognize and emit code for IReadOnlySet<T>, including new APIs like CreateIReadOnlySetInfo and corresponding enum values and method mappings. (src/libraries/System.Text.Json/gen/Helpers/KnownTypeSymbols.cs, src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs, src/libraries/System.Text.Json/gen/JsonSourceGenerator.Parser.cs, src/libraries/System.Text.Json/gen/Model/CollectionType.cs, src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonMetadataServices.Collections.cs, src/libraries/System.Text.Json/ref/System.Text.Json.cs) [1] [2] [3] [4] [5] [6]
• Integrated the new converter into the converter factory logic so that IReadOnlySet<T> types are automatically handled when encountered. (src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableConverterFactory.cs)
• Updated the project file to ensure the new converter is only compiled for supported target frameworks. (src/libraries/System.Text.Json/src/System.Text.Json.csproj)

Test coverage for IReadOnlySet:

• Added comprehensive tests to verify serialization and deserialization of IReadOnlySet<T> and related scenarios, including inheritance and custom interfaces. (src/libraries/System.Text.Json/tests/Common/CollectionTests/CollectionTests.Generic.Read.cs) [1] [2] [3] [4]

Minor fixes:

• Corrected a typo in an exception helper method name from ReturnsJsonConverterFactorty to ReturnsJsonConverterFactory. (src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs, src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverterFactory.cs) [1] [2]

Fixes #91875

[Copilot]

Pull Request Overview

This PR adds support for IReadOnlySet<T> serialization/deserialization to System.Text.Json. The implementation creates a new converter that uses HashSet<T> as the concrete type for IReadOnlySet<T> interface deserialization.

• Adds IReadOnlySetOfTConverter<TCollection, TElement> converter that deserializes JSON arrays to HashSet<T> instances
• Integrates the new converter into the converter factory with appropriate conditional compilation
• Adds comprehensive test coverage for both generic and object-typed IReadOnlySet<T> scenarios

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
IReadOnlySetOfTConverter.cs	New converter implementation for IReadOnlySet<T> using HashSet<T> as backing type
IEnumerableConverterFactory.cs	Integrates IReadOnlySet<T> converter into the factory with conditional compilation
System.Text.Json.csproj	Adds the new converter file to the project
ThrowHelper.Serialization.cs	Fixes typo in method name from "Factorty" to "Factory"
JsonConverterFactory.cs	Updates method call to use corrected spelling
Array.ReadTests.cs	Adds test methods for IReadOnlySet<T> deserialization
ReferenceHandlerTests.cs	Adds JsonSerializable attributes for IReadOnlySet<T> test classes
TestData.cs	Includes IReadOnlySet<T> test cases in success test data
TestClasses.cs	Adds test class definitions and minor formatting change to dictionary initialization

[eiriktsarpalis]

This would also require updates to the source generator so IReadOnlySet is recognized and relevant code gets generated.

[sander1095]

This would also require updates to the source generator so IReadOnlySet is recognized and relevant code gets generated.

@eiriktsarpalis
Any pointers to where I need to get started on this? A nudge to a file would be enough, I can check existing code patterns and call sites to hopefully figure the rest out.

[eiriktsarpalis]

Sure, you can get started by looking at how ISet<T> is being handled today, presumably IReadOnlySet<T> would get handled identically:

runtime/src/libraries/System.Text.Json/gen/JsonSourceGenerator.Parser.cs

Lines 844 to 848 in ca29ebb

	else if ((actualTypeToConvert = type.GetCompatibleGenericBaseType(_knownSymbols.ISetOfTType)) != null)
	{
	collectionType = CollectionType.ISet;
	valueType = actualTypeToConvert.TypeArguments[0];
	}

[sander1095]

@eiriktsarpalis I've made changes to the source generators. Can you provide a check to see if this was done to your satisfaction? Also: If the unit tests pass, can I then assume the source generator implementation is succesful? I am not really sure how to test source generators this in the repo itself, so any tips on that would be great (if succesful unit tests aren't enough).

Thanks for your time!

[Copilot]

Pull Request Overview

Copilot reviewed 24 out of 24 changed files in this pull request and generated 2 comments.

[sander1095]

Hi @eiriktsarpalis and @huoyaoyuan !

I've spent quite a bit of time on this PR in the last 2 weeks. I am fairly certain support for IReadOnlySet is solid.

When I create a little test project and run JsonSerializer.Deserialize<IReadOnlySet<int>>("[1]"), the code works!

I have added tests for more in-depth coverage, but there's still some tests (especially for source generation) that fail, and I can't really figure out why. I've tried to dive deeper into these, but when I attach a debugger to the tests, nothing happens, and I've tried on WSL, Dev Container and Visual Studio.

Anyway, I believe this PR is at the point where it can get a review by the team. My goal is to obtain the following:

• Some help/guidance on WHY remaining tests are failing, and how I can start approaching a fix. If the team can spare a bit of time to run this PR locally and guide me through what's going wrong, I'd really appreciate it!
• Feedback on the core parts of the PR (Especially IReadOnlySetOfTConverter).
• Feedback on current test coverage, and potential missing tests, or tests I should not have deleted in the last batch of commits.
  • In the last commit batch I have removed several test cases because I believe they are not relevant for IReadOnlySet.

Final question:
If this PR approaches acceptability but not merge-ability, could a team member assign hacktoberfest-accepted label ;)?

[huoyaoyuan]

It's prioritized to finalize .NET 10 work in this month. I'm not a member of the team and can only provide auxiliary review.

[sander1095]

I've been looking at the PR from @jozkee that added support for Memory<>/ReadOnlyMemory<>, and this PR from @eiriktsarpalis that added support for IAsyncEnumerable. I believe my PR is (pretty much) in the same state as those PRs, so I believe a real PR review can be started (after the API review process is done: #121314 )

So, I'll need a PR review from a fellow contributor/team member with some guidance on how to fix the last tests. (@eiriktsarpalis ).

The last 6(!) tests that fail are copies of the same 2, regarding to source generation. Some help here would be welcome. I believe it might just be related to how I set up the tests.

Looking forward to continue working on this PR after that is done!

[sander1095]

TODO: I'd like to check this with the team. I'll try to find some time this week/next week to write the tests to check if they succeed or not. :)