Modernize System.Text.Json product code

[eiriktsarpalis]

Adopts modern C# syntax in System.Text.Json product sources without changing behavior or public API.

• Replaces 33 single-use private backing fields with C# 14 field-backed properties while preserving validation and side effects.
• Converts six single-expression methods to expression-bodied members.
• Replaces 415 built-in null comparisons with is null or is not null.
• Replaces 32 stable constant and range comparisons with equivalent or, not, and relational patterns.

The pattern audit deliberately retains 56 null comparisons that bind to user-defined reflection equality operators and 19 compound checks whose conversion would reduce property or mutable-field reads. Project configuration and tests are unchanged. I also audited escaped literals and formatting calls, but retained the existing forms where raw strings or interpolation would not improve readability or would bypass localized resource formatting.

Validation

• build.cmd clr+libs -rc release
• System.Text.Json.csproj across net462, netstandard2.0, net10.0, and net11.0
• dotnet build /t:test for the main System.Text.Json tests and all four Roslyn 3.11/4.4 source-generation test projects
• 129,884 tests: 129,867 passed, 17 skipped, 0 failed

Note

This pull request was prepared by GitHub Copilot.

[azure-pipelines]

Azure Pipelines:
Successfully started running 3 pipeline(s).
12 pipeline(s) were filtered out due to trigger conditions.
There may be pipelines that require an authorized user to comment /azp run to run.

[dotnet-policy-service]

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

[Copilot]

Pull request overview

This PR updates System.Text.Json product sources to use newer C# syntax in a behavior-preserving way, primarily by replacing single-use private backing fields with field-backed properties and by converting a handful of trivial methods to expression-bodied members.

Changes:

• Converted several properties from explicit private backing fields to C# field-backed properties (using field) while keeping existing validation/side effects in setters.
• Converted multiple single-expression helper methods/wrappers to expression-bodied members.
• Kept the changes scoped to implementation details (no new members introduced in the reviewed diffs).

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReadStackFrame.cs	Converts simple type-kind predicates to expression-bodied methods.
src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonTypeInfo.cs	Migrates several callback/configuration properties to field-backed properties while preserving validation in setters.
src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonPropertyInfo.cs	Migrates several configuration properties to field-backed properties while preserving VerifyMutable() and validation logic.
src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonPolymorphismOptions.cs	Converts configuration properties (including defaulting behavior) to field-backed properties.
src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonConverter.cs	Converts ConverterStrategy to a field-backed init-only property while retaining side-effect initialization in init.
src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ConfigurationList.cs	Converts thin wrappers over _list to expression-bodied members.
src/libraries/System.Text.Json/src/System/Text/Json/Schema/JsonSchema.cs	Converts many schema keyword properties to field-backed properties, keeping VerifyMutable() enforcement and initial values.
src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.MultiSegment.cs	Converts CaptureState to an expression-bodied method without changing the captured values.

[adamsitnik]

LGTM

[Copilot]

Pull request overview

Copilot reviewed 114 out of 114 changed files in this pull request and generated no new comments.

[github-actions]

Workflow state for the Holistic Review Orchestrator.

{
  "version": 5,
  "last_dispatched_commit": "6c94dc327cecedf449638d0b4c5595e9d1167cc6",
  "last_dispatched_base_ref": "main",
  "last_dispatched_base_sha": "034f7f5c843988fd82ddfb8369b27c67ab986c86",
  "last_reviewed_commit": "6c94dc327cecedf449638d0b4c5595e9d1167cc6",
  "last_reviewed_base_ref": "main",
  "last_reviewed_base_sha": "034f7f5c843988fd82ddfb8369b27c67ab986c86",
  "last_recorded_worker_run_id": "29687161478",
  "review_attempt_commit": "",
  "review_attempt_base_ref": "",
  "review_attempt_count": 0,
  "max_review_attempts": 5,
  "review_history_format": "holistic-review-disclosure-v1",
  "review_history": [
    {
      "commit": "6c94dc327cecedf449638d0b4c5595e9d1167cc6",
      "review_id": 4730768943
    }
  ]
}

[github-actions]

Holistic Review

Motivation: Adopting modern C# syntax (C# 14 field-backed properties, is null/is not null, relational/or/and patterns, expression-bodied members) in System.Text.Json product code is a reasonable, low-risk readability/consistency improvement. The area builds with LangVersion=preview, so the field keyword is supported.

Approach: The change is purely syntactic. Field-to-field conversions preserve all validation (VerifyMutable()), side effects (_isConfigured = true, CanUseDirectReadOrWrite/RequiresReadAhead in the ConverterStrategy init), and default initializers (e.g. JsonSchemaType.Any). Backing fields that are still referenced from other members or derived types (_effectiveConverter) were correctly left untouched, and fully-removed backing fields (_converterStrategy, _customConverter, _typeDiscriminatorPropertyName, etc.) have no remaining references. Pattern-matching rewrites are logically equivalent to the original boolean expressions. The author states the deliberate retention of null comparisons that bind to reflection equality operators, avoiding a real behavioral pitfall.

Summary: ✅ LGTM. Spot-checked the field-keyword conversions in JsonSchema, JsonPolymorphismOptions, JsonPropertyInfo, and JsonConverter (side effects and defaults preserved), confirmed removed backing fields are unreferenced, and reviewed a sample of the is/or/and pattern rewrites for semantic equivalence. No behavioral or public-API changes; project config and tests are unchanged. Verification rests on the author's reported full clr+libs build and passing test run (129,867 passed / 0 failed), which a reviewer worker cannot reproduce here — CI should confirm the multi-target build (net462/netstandard2.0/net10.0/net11.0) since field is a newer language feature.

---

Detailed Findings

✅ Field-backed property conversions — semantics preserved

Each converted property retains its setter validation and side effects. Notable non-trivial cases verified: JsonSchema.Type keeps its = JsonSchemaType.Any initializer; JsonPolymorphismOptions setters still set _isConfigured = true; TypeDiscriminatorPropertyName keeps get => field ?? JsonSerializer.TypePropertyName; JsonConverter.ConverterStrategy init still computes CanUseDirectReadOrWrite/RequiresReadAhead before assigning field.

✅ Backing-field removal is compile-safe

Fields converted to the field keyword are no longer referenced elsewhere; fields still referenced from other members or subclasses (_effectiveConverter) were intentionally retained.

✅ Pattern-matching rewrites — logically equivalent

Rewrites such as initialSize is > OneMegabyte and <= 4 * OneMegabyte, tokenType is JsonTokenType.StartArray or JsonTokenType.StartObject, and nextByte is not ((byte)'.' or (byte)'E' or (byte)'e') preserve the original truth tables and precedence.

💡 CI multi-target confirmation

Since this relies on the field contextual keyword and preview language features, the value of this review hinges on the full CI matrix (including the down-level target frameworks) building successfully. No action needed beyond letting CI complete.

Note

This review was generated by this repository's Holistic Review agentic workflow to complement the built-in Copilot review.

Generated by Holistic Review · 119.2 AIC · ⌖ 10.7 AIC · ⊞ 10K