Support type-level JsonIgnoreCondition via [JsonIgnore] on classes, structs, and interfaces by Copilot · Pull Request #124646 · dotnet/runtime

Copilot · 2026-02-20T14:41:40Z

Description

[JsonIgnore(Condition = ...)] can now be applied at the type level to set a default JsonIgnoreCondition for all properties and fields, eliminating per-property duplication:

[JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
class MyPoco
{
    public string? PropA { get; set; }
    public string? PropB { get; set; }
    public string? PropC { get; set; }
}

Property-level [JsonIgnore] overrides the type-level setting. WhenWritingNull is silently skipped for non-nullable value types, matching JsonSerializerOptions.DefaultIgnoreCondition semantics. JsonIgnoreCondition.Always is rejected at the type level as invalid configuration — the reflection path throws InvalidOperationException, and the source generator emits SYSLIB1226 warning diagnostic and ignores the attribute.

Changes

API surface: Expanded JsonIgnoreAttribute AttributeUsage to include Class | Struct | Interface, with API compat suppressions for the AttributeUsage change in both the shared framework baseline (ApiCompatBaseline.NetCoreAppLatestStable.xml) and the package-level baseline (CompatibilitySuppressions.xml for net10.0, net462, netstandard2.0)
Reflection resolver (DefaultJsonTypeInfoResolver.Helpers.cs): Falls back to type-level [JsonIgnore] when no member-level attribute is present. Uses typeInfo.Type (root serialized type) so type-level attributes on derived classes apply to inherited base-class properties. Throws InvalidOperationException for JsonIgnoreCondition.Always at the type level.
Source generator (JsonSourceGenerator.Parser.cs): Reads type-level [JsonIgnore] in ProcessTypeCustomAttributes using cached JsonIgnoreAttributeType symbol from KnownTypeSymbols.cs, threads it through to property parsing as a fallback. Emits SYSLIB1226 diagnostic for JsonIgnoreCondition.Always at the type level.
Diagnostic: Added SYSLIB1226 diagnostic descriptor, resource strings (including XLF translations), and updated list-of-diagnostics.md
Tests: Covers WhenWritingNull, WhenWritingDefault, Always (invalid config), property-level override, struct, inheritance, and deserialization scenarios across both reflection and source gen paths. Includes source generator unit test for the SYSLIB1226 diagnostic.

Original prompt

This section details on the original issue you should resolve

<issue_title>It should be possible to specify JsonIgnoreCondition's on the type level</issue_title>
<issue_description>## Motivation

There's a substantial amount of duplication in the following code:

class MyPoco
{
    [JsonIgnore(JsonIgnoreCondition.WhenWritingNull)]
    public string? PropA { get; set; }

    [JsonIgnore(JsonIgnoreCondition.WhenWritingNull)]
    public string? PropB { get; set; }

    [JsonIgnore(JsonIgnoreCondition.WhenWritingNull)]
    public string? PropC { get; set; }
}

that could be eliminated using a type-level declaration:

[JsonIgnore(JsonIgnoreCondition.WhenWritingNull)]
class MyPoco
{
    public string? PropA { get; set; }

    public string? PropB { get; set; }

    public string? PropC { get; set; }
}

API Proposal

namespace System.Text.Json.Serialization;

-[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Interface | AttributeTargets.AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
public partial class JsonIgnoreAttribute;

cc @stephentoub</issue_description>

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

Fixes It should be possible to specify JsonIgnoreCondition's on the type level #108231

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dotnet-policy-service · 2026-02-20T14:51:45Z

Tagging subscribers to this area: @dotnet/area-system-text-json
See info in area-owners.md if you want to be subscribed.

…n resolver, source generator) Co-authored-by: eiriktsarpalis <[email protected]>

…on value types Co-authored-by: eiriktsarpalis <[email protected]>

…dd inheritance and deserialization tests Co-authored-by: eiriktsarpalis <[email protected]>

eiriktsarpalis

@copilot

eiriktsarpalis · 2026-02-20T17:55:27Z

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

                    }

+                    if (attributeType?.ContainingAssembly.Name == SystemTextJsonNamespace &&
+                        attributeType.ToDisplayString() == JsonIgnoreAttributeFullName)


@copilot rather than allocating a full string every type the attribute gets compared, use the existing pattern in KnownSymbols.cs (or whatever it's called) where the attribute symbol is cached for the current compilation.

Switched to using SymbolEqualityComparer.Default.Equals(attributeType, _knownSymbols.JsonIgnoreAttributeType) with a cached JsonIgnoreAttributeType property added to KnownTypeSymbols.cs, matching the pattern used by other attribute types like JsonDerivedTypeAttributeType. Commit 1f73332.

eiriktsarpalis · 2026-02-20T17:55:58Z

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

+                        else if (namedArgs.Length == 1 &&
+                            namedArgs[0].Value.Type?.ToDisplayString() == JsonIgnoreConditionFullName)
+                        {
+                            typeIgnoreCondition = (JsonIgnoreCondition)namedArgs[0].Value.Value!;


What happens if the JsonIgnoreCondition is Always on the type level? Surely that would be invalid configuration? Add a diagnostic, a source generator unit test and a testing covering runtime behavior for both the generator and relection-based serializers.

Added handling for JsonIgnoreCondition.Always at the type level:

Reflection path: throws InvalidOperationException (reusing SR.DefaultIgnoreConditionInvalid), consistent with JsonSerializerOptions.DefaultIgnoreCondition behavior

Source generator: emits SYSLIB1226 warning diagnostic and ignores the attribute (resets typeIgnoreCondition to null)

Source gen unit test: JsonIgnoreConditionAlwaysOnTypeWarns in JsonSourceGeneratorDiagnosticsTests.cs

Runtime tests: JsonIgnoreCondition_TypeLevel_Always_ThrowsInvalidOperation (virtual in base, overridden in source gen tests to verify properties serialize normally when the attribute is ignored)

Commit 1f73332.

…YSLIB1226 diagnostic Co-authored-by: eiriktsarpalis <[email protected]>

eiriktsarpalis · 2026-02-24T11:02:03Z

src/libraries/apicompat/ApiCompatBaseline.NetCoreAppLatestStable.xml

  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0015</DiagnosticId>
+    <Target>T:System.Text.Json.Serialization.JsonIgnoreAttribute:[T:System.AttributeUsageAttribute]</Target>


@copilot this is still causing API compatibility errors. Please address accordingly.

Added CompatibilitySuppressions.xml in src/libraries/System.Text.Json/src/ for package validation (CP0015 suppression for JsonIgnoreAttribute's AttributeUsageAttribute change across net10.0, net462, and netstandard2.0 TFMs). The existing suppression in ApiCompatBaseline.NetCoreAppLatestStable.xml covers the shared framework API compat check, but the package-level validation also needs its own suppression file since System.Text.Json ships as a multi-TFM NuGet package. Commit fc730c9.

…tion Co-authored-by: eiriktsarpalis <[email protected]>

Copilot · 2026-02-24T11:16:30Z

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

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Initial plan

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Copilot AI assigned Copilot and eiriktsarpalis Feb 20, 2026

Copilot started work on behalf of eiriktsarpalis February 20, 2026 14:42 View session

github-actions bot added the area-System.Text.Json label Feb 20, 2026

Copilot AI and others added 3 commits February 20, 2026 15:14

Add type-level JsonIgnoreAttribute support (AttributeUsage, reflectio…

8aa0d39

…n resolver, source generator) Co-authored-by: eiriktsarpalis <[email protected]>

Add tests for type-level JsonIgnoreAttribute; handle WhenWritingNull …

ab2fe26

…on value types Co-authored-by: eiriktsarpalis <[email protected]>

Fix inheritance: use typeInfo.Type for type-level attribute lookup; a…

6ff4713

…dd inheritance and deserialization tests Co-authored-by: eiriktsarpalis <[email protected]>

Copilot AI changed the title ~~[WIP] Add JsonIgnoreCondition support at type level~~ Support type-level JsonIgnoreCondition via [JsonIgnore] on classes, structs, and interfaces Feb 20, 2026

Copilot AI requested a review from eiriktsarpalis February 20, 2026 15:36

Copilot finished work on behalf of eiriktsarpalis February 20, 2026 15:36

eiriktsarpalis reviewed Feb 20, 2026

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Copilot started work on behalf of eiriktsarpalis February 20, 2026 17:57 View session

build-analysis bot mentioned this pull request Feb 20, 2026

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

Open

Address review: use cached symbol, reject Always at type level with S…

1f73332

…YSLIB1226 diagnostic Co-authored-by: eiriktsarpalis <[email protected]>

Copilot AI requested a review from eiriktsarpalis February 20, 2026 18:47

Copilot finished work on behalf of eiriktsarpalis February 20, 2026 18:47

eiriktsarpalis reviewed Feb 24, 2026

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Copilot started work on behalf of eiriktsarpalis February 24, 2026 11:02 View session

Add CompatibilitySuppressions.xml for System.Text.Json package valida…

fc730c9

…tion Co-authored-by: eiriktsarpalis <[email protected]>

Copilot AI requested a review from eiriktsarpalis February 24, 2026 11:16

Copilot finished work on behalf of eiriktsarpalis February 24, 2026 11:16

build-analysis bot mentioned this pull request Feb 24, 2026

Android WebSocket failure #121518

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Support type-level JsonIgnoreCondition via [JsonIgnore] on classes, structs, and interfaces#124646

Support type-level JsonIgnoreCondition via [JsonIgnore] on classes, structs, and interfaces#124646
Copilot wants to merge 6 commits intomainfrom
copilot/add-jsonignorecondition-type-level

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Description

Changes

API Proposal

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