.NET 6 Preview 7 Blazor WebAssembly won't build if you are using a JsonSerializerContext implementation

In preview 6, you introduced the Json source generator, and I created a “MyJsonContext” to enable the source generator.

    [JsonSerializable(typeof(JsonData))]
    internal partial class MyJsonContext : JsonSerializerContext
    {
    }

Now, in preview 7 the System.Text.Json.SourceGeneration assembly gets added to references twice.

This leads to build failure as they both generate the same code!

You can see the duplicate reference by simply creating a new BlazorWebAssembly project, but you need to implement a JsonSerializerContext to see the errors.

Configuration

.NET version 6.0.100-preview.7.21379.14 Windows 11 22000.120 Architecture x64 Browser not relevant as the project won’t build.

Regression?

Worked in .NET 6 Preview 6

Other information

Errors from build:

1>Build FAILED. 1> 1>C:\Users\aaaaa\source\repos\JsonPerfTest\System.Text.Json.SourceGeneration\System.Text.Json.SourceGeneration.JsonSourceGenerator\MyJsonContext.g.cs(6,6,6,60): error CS0579: Duplicate ‘global::System.CodeDom.Compiler.GeneratedCodeAttribute’ attribute 1>C:\Users\aaaaa\source\repos\JsonPerfTest\System.Text.Json.SourceGeneration\System.Text.Json.SourceGeneration.JsonSourceGenerator\MyJsonContext.String.g.cs(7,101,7,108): error CS0102: The type ‘MyJsonContext’ already contains a definition for ‘_String’ 1>C:\Users\aaaaa\source\repos\JsonPerfTest\System.Text.Json.SourceGeneration\System.Text.Json.SourceGeneration.JsonSourceGenerator\MyJsonContext.String.g.cs(8,100,8,106): error CS0102: The type ‘MyJsonContext’ already contains a definition for ‘String’ …68 of these errors in total

[ericstj]

A better workaround for this bug is the following as it addresses all cases:

  <Target Name="FixPackageConflictOverrides" AfterTargets="ResolveTargetingPackAssets">
    <PropertyGroup>
      <PackageConflictPreferredPackages>$([MSBuild]::Unescape($(PackageConflictPreferredPackages)))</PackageConflictPreferredPackages>
    </PropertyGroup>
  </Target>

[SQL-MisterMagoo]

Here’s a repro - I don’t know what “grab a binlog” means, sorry.

https://github.com/SQL-MisterMagoo/Issue57249