Fix JsonSourceGenerator verbatim identifier handling in property initializers

[Copilot]

main PR

Description

JsonSourceGenerator emitted bare C# keywords instead of verbatim identifiers (@else → else) when generating property initializers for init-only properties, causing compilation errors.

Root cause: PropertyInitializerGenerationSpec.Name was set to MemberName (raw identifier) instead of NameSpecifiedInSourceCode (includes @ prefix for reserved keywords).

Fix: Single line change in JsonSourceGenerator.Parser.cs:

// Before
Name = property.MemberName,
// After  
Name = property.NameSpecifiedInSourceCode,

Repro:

class MyClass { public string @else { get; init; } }

[JsonSerializable(typeof(MyClass))]
partial class Ctx : JsonSerializerContext;

Previously generated invalid code: new MyClass(){ else = ... } instead of new MyClass(){ @else = ... }.

Customer Impact

Any type with init-only properties using C# reserved keywords as names fails to compile with source generation.

Regression

No, this is a long-standing bug in the source generator.

Testing

• Added unit test InitOnlyPropertyWithReservedKeywordName_CompilesSuccessfully using a regular class to ensure compatibility across all targets without conditional compilation
• All 153 source generator unit tests pass on net11.0 with both Roslyn 4.4 and Roslyn 3.11

Risk

Low. Single line change affecting only the name used in generated property initializers. The fix uses the same NameSpecifiedInSourceCode property already used elsewhere in the generator for the same purpose.

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>JsonSourceGenerator misinterprets @ verbatim identifiers.</issue_title>
<issue_description>### Description

JsonSourceGenerator does not correctly handle C# verbatim identifiers and confuses them during code generation.

Reproduction Steps

$ cat <<EOF | dotnet run -
using System.Text.Json;
using System.Text.Json.Serialization;
Console.Write(JsonSerializer.Deserialize("""{"else":{}}""",Ctx.Default.A));
[JsonSerializable(typeof(A))] partial class Ctx : JsonSerializerContext;
record A { public A? @else { get; init; } }
EOF
~/System.Text.Json.SourceGeneration/System.Text.Json.SourceGeneration.JsonSourceGenerator/Ctx.A.g.cs(41,9): error CS8802: Only one compilation unit can have top-level statements.

The build failed. Fix the build errors and run again.

Expected behavior

$ cat <<EOF | dotnet run -
using System.Text.Json;
using System.Text.Json.Serialization;
Console.Write(JsonSerializer.Deserialize("""{"else":{}}""",Ctx.Default.A));
[JsonSerializable(typeof(A))] partial class Ctx : JsonSerializerContext;
record A { public A? @else { get; init; } }
EOF
A { else = A { else =  } }

Actual behavior

.

Regression?

No response

Known Workarounds

$ cat <<EOF | dotnet run -
#:property PublishAot=false
using System.Text.Json;
Console.Write(JsonSerializer.Deserialize<A>("""{"else":{}}"""));
record A { public A? @else { get; init; } }
EOF
A { else = A { else =  } }

$ cat <<EOF | dotnet run -
using System.Text.Json;
using System.Text.Json.Serialization;
Console.Write(JsonSerializer.Deserialize("""{"else":{}}""",Ctx.Default.A));
[JsonSerializable(typeof(A))] partial class Ctx : JsonSerializerContext;
record A { [JsonPropertyName("else")] public A? Else { get; init; } }
EOF
A { Else = A { Else =  } }

Configuration

$ dotnet --version
10.0.100

Other information

No response</issue_description>

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

• Fixes JsonSourceGenerator misinterprets @ verbatim identifiers. #122732

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[Copilot]

Pull request overview

This PR fixes a bug in the JsonSourceGenerator where verbatim identifiers (e.g., @else) for C# reserved keywords were not properly handled when generating property initializers for init-only properties, causing compilation errors.

Key changes:

• Changed PropertyInitializerGenerationSpec.Name to use NameSpecifiedInSourceCode instead of MemberName to preserve the @ prefix for reserved keywords
• Added regression test for init-only properties with reserved keyword names

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/System.Text.Json/gen/JsonSourceGenerator.Parser.cs	Fixed property initializer generation to use NameSpecifiedInSourceCode which includes the @ prefix for verbatim identifiers
src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/JsonSourceGeneratorTests.cs	Added regression test InitOnlyPropertyWithReservedKeywordName_CompilesSuccessfully to verify the fix

[stephentoub]

@copilot, why are these necessary? Can the test be tweaked so that it still tests what it needs to be test but can work on all targets?

[Copilot]

Changed the test to use a regular class instead of record, which removes the need for the conditional compilation guards while still testing the same code path for verbatim identifier handling in property initializers. Fixed in af6c4c0.