JsonSourceGenerator - ArgumentException key already added.

[fbrosseau]

Description

6.0.100-preview.7.21379.14 on Windows x64

Following code crashes the JsonSourceGenerator:

    [JsonSerializable(typeof(B))]
    public partial class MySerializerContext : JsonSerializerContext
    {
    }

    public class B : A
    {
        [JsonIgnore]
        public override int I => 0;
    }

    public abstract class A
    {
        [JsonIgnore]
        public abstract int I { get; }
    }

With the following:

1>CSC : warning CS8785: Generator 'JsonSourceGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'ArgumentException' with message 'An item with the same key has already been added.'

Workarounds:
Interestingly if I change A.I to be virtual instead of abstract, it works.
Also, if I remove JsonIgnore from the base (and keep it abstract), it also works.
So the workarounds are easy.

 	System.Text.Json.SourceGeneration.dll!System.Text.Json.SourceGeneration.JsonSourceGenerator.Parser.CacheMember(System.Text.Json.SourceGeneration.PropertyGenerationSpec propGenSpec, ref System.Collections.Generic.List<System.Text.Json.SourceGeneration.PropertyGenerationSpec> propGenSpecList, ref System.Collections.Generic.Dictionary<string, System.Text.Json.SourceGeneration.PropertyGenerationSpec> ignoredMembers)	Unknown
 	System.Text.Json.SourceGeneration.dll!System.Text.Json.SourceGeneration.JsonSourceGenerator.Parser.GetOrAddTypeGenerationSpec(System.Type type, System.Text.Json.Serialization.JsonSourceGenerationMode generationMode)	Unknown
 	System.Text.Json.SourceGeneration.dll!System.Text.Json.SourceGeneration.JsonSourceGenerator.Parser.GetRootSerializableType(Microsoft.CodeAnalysis.SemanticModel compilationSemanticModel, Microsoft.CodeAnalysis.CSharp.Syntax.AttributeSyntax attributeSyntax, System.Text.Json.Serialization.JsonSourceGenerationMode generationMode)	Unknown
 	System.Text.Json.SourceGeneration.dll!System.Text.Json.SourceGeneration.JsonSourceGenerator.Parser.GetGenerationSpec(System.Collections.Generic.List<Microsoft.CodeAnalysis.CSharp.Syntax.ClassDeclarationSyntax> classDeclarationSyntaxList)	Unknown
 	System.Text.Json.SourceGeneration.dll!System.Text.Json.SourceGeneration.JsonSourceGenerator.Execute(Microsoft.CodeAnalysis.GeneratorExecutionContext executionContext)	Unknown
 	Microsoft.CodeAnalysis.dll!Microsoft.CodeAnalysis.GeneratorDriver.RunGeneratorsCore(Microsoft.CodeAnalysis.Compilation compilation, Microsoft.CodeAnalysis.DiagnosticBag diagnosticsBag, System.Threading.CancellationToken cancellationToken)	Unknown

Tagging subscribers to this area: @eiriktsarpalis, @layomia
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Issue Details

---

Description

6.0.100-preview.7.21379.14 on Windows x64

Following code crashes the JsonSourceGenerator:

    [JsonSerializable(typeof(B))]
    public partial class MySerializerContext : JsonSerializerContext
    {
    }

    public class B : A
    {
        [JsonIgnore]
        public override int I => 0;
    }

    public abstract class A
    {
        [JsonIgnore]
        public abstract int I { get; }
    }

With the following:

1>CSC : warning CS8785: Generator 'JsonSourceGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'ArgumentException' with message 'An item with the same key has already been added.'

Workarounds:
Interestingly if I change A.I to be virtual instead of abstract, it works.
Also, if I remove JsonIgnore from the base (and keep it abstract), it also works.
So the workarounds are easy.

 	System.Text.Json.SourceGeneration.dll!System.Text.Json.SourceGeneration.JsonSourceGenerator.Parser.CacheMember(System.Text.Json.SourceGeneration.PropertyGenerationSpec propGenSpec, ref System.Collections.Generic.List<System.Text.Json.SourceGeneration.PropertyGenerationSpec> propGenSpecList, ref System.Collections.Generic.Dictionary<string, System.Text.Json.SourceGeneration.PropertyGenerationSpec> ignoredMembers)	Unknown
 	System.Text.Json.SourceGeneration.dll!System.Text.Json.SourceGeneration.JsonSourceGenerator.Parser.GetOrAddTypeGenerationSpec(System.Type type, System.Text.Json.Serialization.JsonSourceGenerationMode generationMode)	Unknown
 	System.Text.Json.SourceGeneration.dll!System.Text.Json.SourceGeneration.JsonSourceGenerator.Parser.GetRootSerializableType(Microsoft.CodeAnalysis.SemanticModel compilationSemanticModel, Microsoft.CodeAnalysis.CSharp.Syntax.AttributeSyntax attributeSyntax, System.Text.Json.Serialization.JsonSourceGenerationMode generationMode)	Unknown
 	System.Text.Json.SourceGeneration.dll!System.Text.Json.SourceGeneration.JsonSourceGenerator.Parser.GetGenerationSpec(System.Collections.Generic.List<Microsoft.CodeAnalysis.CSharp.Syntax.ClassDeclarationSyntax> classDeclarationSyntaxList)	Unknown
 	System.Text.Json.SourceGeneration.dll!System.Text.Json.SourceGeneration.JsonSourceGenerator.Execute(Microsoft.CodeAnalysis.GeneratorExecutionContext executionContext)	Unknown
 	Microsoft.CodeAnalysis.dll!Microsoft.CodeAnalysis.GeneratorDriver.RunGeneratorsCore(Microsoft.CodeAnalysis.Compilation compilation, Microsoft.CodeAnalysis.DiagnosticBag diagnosticsBag, System.Threading.CancellationToken cancellationToken)	Unknown

Author:	fbrosseau
Assignees:	-
Labels:	area-System.Text.Json, untriaged
Milestone:	-

[am11]

Another non-abstract case where this warning gets triggered is when we try to hide the member of base class using new modifier:

using System;
using System.Text.Json;
using System.Text.Json.Serialization;

Console.WriteLine(JsonSerializer.Serialize(new B(), typeof(B), new MySerializerContext()));

[JsonSerializable(typeof(B))]
public partial class MySerializerContext : JsonSerializerContext
{
}

public class B : A
{
    [JsonIgnore]
    public new int I => 0;
}

public abstract class A
{
    [JsonIgnore]
    public int I { get; }
}

CSC : warning CS8785: Generator 'JsonSourceGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'ArgumentException' with message 'An item with the same key has already been added. Key: I'

[eiriktsarpalis]

I can reproduce both with the RC2 SDK. The fact that JsonIgnore is not able to suppress the error is worrying -- we should fix this for 6.0.

[steveharter]

For the latter case from @am11 it looks like normal serialization also fails:

  // This throws System.ArgumentException:An item with the same key has already been added. Key: Ignored_New_Property
  string json = JsonSerializer.Serialize(new ConcreteDerivedClass());

  public class ConcreteDerivedClass : AbstractBaseClass
  {
      [JsonIgnore]
      public new int Ignored_New_Property { get; set; }
  }
  
  public abstract class AbstractBaseClass
  {
      [JsonIgnore]
      public int Ignored_New_Property { get; set; }
  }

So I created #59675 to address that separately.