System.Text.Json code generator creates metadata for classes that are explicitly ignored #76937

Description

I have a few classes I'm trying to convert to using System.Text.Json codegenerator to better support trimming.
However I'm having trouble getting the code generator to not create metadata for classes that are ignored. This causes sometimes 100s of classes to get metadata generated which would never be used, as well as often hitting code it can't even generate correct code for.

Issue is likely related to this .net7 specific issue: #76807

Reproduction Steps

Add the following code to a .NET 6 app/library:

    [JsonSerializable(typeof(MyObject))]
    [JsonSourceGenerationOptions(GenerationMode = JsonSourceGenerationMode.Metadata, IgnoreReadOnlyFields = true)]
    internal partial class MyObjectSerializationContext : JsonSerializerContext
    {
    }
    public class MyObject
    {
        [JsonPropertyName("test")]
        public string? Test { get; set; }
        [JsonIgnore]
        private readonly ComplexObject? _data; // Metadata generated for this type. Why?!?
    }

    public class ComplexObject
    {
        private protected object _thisLock = new object(); // This causes code gen problem
    }

Compile and observe the build errors and the classes that metadata is generated for.

Expected behavior

Project builds with out errors. No metadata generated for ComplexObject or anything else ignored.

Actual behavior

1>E:\sources.tmp\TrimTest\ClassLibrary1\System.Text.Json.SourceGeneration\System.Text.Json.SourceGeneration.JsonSourceGenerator\MyObjectSerializationContext.ComplexObject.g.cs(58,85,58,94): error CS0122: 'ComplexObject._thisLock' is inaccessible due to its protection level
1>E:\sources.tmp\TrimTest\ClassLibrary1\System.Text.Json.SourceGeneration\System.Text.Json.SourceGeneration.JsonSourceGenerator\MyObjectSerializationContext.ComplexObject.g.cs(59,92,59,101): error CS0122: 'ComplexObject._thisLock' is inaccessible due to its protection level

I don't get why it is even trying to generate anything for ComplexObject - I explicitly told it to ignore that field. This happens with .net6 also though (also tested 6.0.6 nuget package).

In my specific case, ComplexObject is potentially a huge object graph and the result is I'm getting metadata generated for hundreds of classes.

Regression?

No response

Known Workarounds

I could add [JsonIgnore] on _thisLock, but that only addresses this specific class - I don't really want to add json ignore to every field in all my classes that causes problems, when these classes aren't even meant for JSON serialization, and I don't want to bloat my assembly size with all this extraneous metadata generated.

Configuration

.NET 6.0.404

Other information

No response