Add IReadOnlySet support to System.Text.Json by sander1095 · Pull Request #120306 · dotnet/runtime

sander1095 · 2025-10-01T20:35:27Z

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>.

Minor fixes:

Corrected a typo in an exception helper method name from ReturnsJsonConverterFactorty to ReturnsJsonConverterFactory.

Fixes #91875

This is based on existing test cases for IReadOnlyList and ISet

I'm pretty sure this is not the right direction, but it helps me with being able to run tests against an initial working implementation I'll work on next. I'll discuss the current #IF !NETFRAMEWORK code setup with the team when the PR is ready for a first review

This seems useful for code that deserializes to a type that deserializes to a Set type that implements both interfaces.

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

...xt.Json/src/System/Text/Json/Serialization/Converters/Collection/IReadOnlySetOfTConverter.cs

src/libraries/System.Text.Json/tests/Common/TestClasses/TestClasses.cs

...Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableConverterFactory.cs

...xt.Json/src/System/Text/Json/Serialization/Converters/Collection/IReadOnlySetOfTConverter.cs

eiriktsarpalis

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

sander1095 · 2025-10-02T08:04:32Z

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 · 2025-10-02T08:07:11Z

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]; 
        
           }

Also exclude the entirety of IReadOnlySetOfTConverter by moving the #IF up.

@huoyaoyuan

…ck to csproj, which is what @huoyaoyuan (most likely) meant in his PR feedback. As far as I can see, there isn't a modern .NET identifier. Therefore, a check for .NETCoreApp is not enough, because that also includes < NET 5.0. Because of this, I also added a check that we are on .NET 5 or higher. Only then will the file be compiled.

…gh my editor says it is required

sander1095 · 2025-10-04T20:13:37Z

@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!

src/libraries/System.Text.Json/tests/Common/JsonCreationHandlingTests.Generic.cs

@huoyaoyuan

Thanks to @huoyaoyuan for their generous help!

...son/tests/System.Text.Json.SourceGeneration.Tests/Serialization/JsonCreationHandlingTests.cs

sander1095 · 2026-01-13T22:21:09Z

@eiriktsarpalis Please provide feedback on this PR when you (or a teammate) can

…nded). They dont work because of missing population support, and that's because readonly collection dont have population support. This behavior is expected.

eiriktsarpalis · 2026-01-16T07:09:41Z

@sander1095 the test failures suggest that you did not add the new test types to one of the JsonSerializerContexts used to drive the tests.

…xt_json

sander1095 · 2026-01-16T21:21:32Z

@eiriktsarpalis Thanks for that hint!

I ran all the tests locally, and they all succeed now! Now I'm hoping for a succesful pipeline run!

This PR is fully ready for review by the team! I'm curious for the feedback, and excited to see this merged for .NET 11!

eiriktsarpalis

Thank you for this excellent contribution!

Copilot

Pull request overview

Copilot reviewed 25 out of 25 changed files in this pull request and generated 1 comment.

src/libraries/System.Text.Json/tests/Common/CollectionTests/CollectionTests.Generic.Write.cs

…llectionTests.Generic.Write.cs Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

sander1095 added 7 commits October 1, 2025 17:13

Start adding testcases for IReadOnlySet

506bb05

This is based on existing test cases for IReadOnlyList and ISet

Add another test

419b232

Fix typo (Factorty -> Factory)

ad9f947

Add another #IF to a test case

34ec615

Start working on readonlyset converter

4f80f13

Move IReadOnlySet above ISet so ISet has priority.

5bb7f66

This seems useful for code that deserializes to a type that deserializes to a Set type that implements both interfaces.

Copilot AI review requested due to automatic review settings October 1, 2025 20:35

github-actions bot added the area-System.Text.Json label Oct 1, 2025

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Oct 1, 2025

Copilot AI reviewed Oct 1, 2025

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...xt.Json/src/System/Text/Json/Serialization/Converters/Collection/IReadOnlySetOfTConverter.cs Outdated Show resolved Hide resolved

src/libraries/System.Text.Json/tests/Common/TestClasses/TestClasses.cs Outdated Show resolved Hide resolved

sander1095 marked this pull request as draft October 1, 2025 20:37

huoyaoyuan reviewed Oct 2, 2025

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...Json/src/System/Text/Json/Serialization/Converters/Collection/IEnumerableConverterFactory.cs Outdated Show resolved Hide resolved

...xt.Json/src/System/Text/Json/Serialization/Converters/Collection/IReadOnlySetOfTConverter.cs Outdated Show resolved Hide resolved

eiriktsarpalis reviewed Oct 2, 2025

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sander1095 added 5 commits October 4, 2025 15:19

Change #IF pre-processors to PR suggested variant

195a155

Also exclude the entirety of IReadOnlySetOfTConverter by moving the #IF up.

Start adding support for IReadOnlySetOfT for Source Generators

6221944

Add missing newline

587f501

Remove missing newline as I do not see it on GitHub either, even thou…

2c17fa1

…gh my editor says it is required

build-analysis bot mentioned this pull request Oct 4, 2025

Intermittent build failure in AfterSourceBuild: "Could not write state file" #76488

Open

Add more code for source generator support

bdf9655

build-analysis bot mentioned this pull request Oct 4, 2025

Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. dotnet/dnceng#5922

Open

3 tasks

Add many more tests based on patterns of existing ISet tests

9f0f3fe

sander1095 added 2 commits October 4, 2025 20:35

Fix part of the build issues

c3f4662

Fix test

91a1ab0

sander1095 commented Oct 9, 2025

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src/libraries/System.Text.Json/tests/Common/JsonCreationHandlingTests.Generic.cs Outdated Show resolved Hide resolved

Add whitespace

c8dc1d3

sander1095 added 2 commits November 4, 2025 23:01

Remove another comment that I hadnt saved

b6e4d51

Remove unnecessary #ifdefs for source generators

4fa876b

Thanks to @huoyaoyuan for their generous help!

sander1095 commented Nov 4, 2025

View reviewed changes

...son/tests/System.Text.Json.SourceGeneration.Tests/Serialization/JsonCreationHandlingTests.cs Outdated Show resolved Hide resolved

Add extra test for IReadOnlySet

4d927bf

build-analysis bot mentioned this pull request Nov 5, 2025

System.Security.Cryptography.X509Certificates.Tests fails on Linux #120527

Closed

jeffhandley assigned tarekgh Jan 14, 2026

Merge branch 'main' into add-ireadonlyset-support-to-system_text_json

84c61c1

build-analysis bot mentioned this pull request Jan 14, 2026

"We stopped hearing from agent Azure Pipelines 32. Verify the agent machine is running and has a healthy network connection" dotnet/dnceng#1886

Open

3 tasks

Remove comment because I tested the changes and they don't work (inte…

18e3cc9

…nded). They dont work because of missing population support, and that's because readonly collection dont have population support. This behavior is expected.

sander1095 added 2 commits January 16, 2026 21:12

Merge branch 'dotnet:main' into add-ireadonlyset-support-to-system_te…

579db98

…xt_json

Fix Source Gen tests by adding missing JsonSerializable attributes

5d8105c

build-analysis bot mentioned this pull request Jan 17, 2026

[android][arm64] System.Net.Sockets.Tests.SendTo_SyncForceNonBlocking.Datagram_UDP_ShouldImplicitlyBindLocalEndpoint fails with NetworkUnreachable #120526

Open

Merge branch 'main' into add-ireadonlyset-support-to-system_text_json

da4e256

eiriktsarpalis requested a review from Copilot January 20, 2026 09:13

Copilot started reviewing on behalf of eiriktsarpalis January 20, 2026 09:14 View session

eiriktsarpalis approved these changes Jan 20, 2026

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Copilot AI reviewed Jan 20, 2026

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src/libraries/System.Text.Json/tests/Common/CollectionTests/CollectionTests.Generic.Write.cs Outdated Show resolved Hide resolved

eiriktsarpalis and others added 4 commits January 20, 2026 11:24

Update src/libraries/System.Text.Json/tests/Common/CollectionTests/Co…

bc0834a

…llectionTests.Generic.Write.cs Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Fix build error.

36248f6

Merge branch 'main' into add-ireadonlyset-support-to-system_text_json

7ad1234

Merge branch 'main' into add-ireadonlyset-support-to-system_text_json

9524492

eiriktsarpalis merged commit b1d2e4a into dotnet:main Jan 21, 2026
75 of 89 checks passed

sander1095 deleted the add-ireadonlyset-support-to-system_text_json branch January 21, 2026 17:52

dotnet-maestro bot mentioned this pull request Jan 22, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#4351

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sander1095 commented Oct 1, 2025 •

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