Obsoletions with a DiagnosticId still get warnings in generated code

[eerhardt]

Description

This issue is tracking updating the System.Text.Json and ConfigurationBinder source generators to take advantage of dotnet/roslyn#73292 when it is implemented.

Original Description

When the System.Text.Json and ConfigurationBinder source generators generate code against types that have properties with [Obsolete("message", DiagnosticId = "ID01")] attributes, the generated code is emitting warnings that I can't suppress and can't control. The only thing I can do is suppress the warning globally, which isn't ideal because I still want those warnings for my "hand written" code.

Both of those generators already suppress "normal" obsoletions with #pragma warning disable CS0612, CS0618. But since these obsoletion warnings get their own DiagnosticID, those suppressions don't work.

(Note the case I hit was with the Configuration Binder source generator against a class that had an X509Certificate2 property - which has 3 properties with different DiagnosticIDs - SYSLIB0026;SYSLIB0027;SYSLIB0028.)

Reproduction Steps

dotnet build the following project:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <EnableConfigurationBindingGenerator>true</EnableConfigurationBindingGenerator>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Hosting" Version="8.0.0" />
    <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="8.0.1" />
  </ItemGroup>

</Project>

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using System.Text.Json.Serialization;

var builder = Host.CreateApplicationBuilder(args);

var c = new MyClass();
builder.Configuration.Bind(c);

[JsonSerializable(typeof(MyClass))]
public partial class JsonContext : JsonSerializerContext
{
}

public class MyClass
{
    [Obsolete("message", DiagnosticId = "EE01")]
    public string? Name { get; set; }
}

Expected behavior

I shouldn't get warnings that I can't take action against.

Actual behavior

I get the following warnings:

\ConsoleApp119\obj\Debug\net8.0\Microsoft.Extensions.Configuration.Binder.SourceGeneration\Microsoft.Extensions.Configuration.Binder.SourceGeneration.ConfigurationBindingGenerator\BindingExtensions.g.cs(65,17): warning EE01: 'MyClass.Name' is obsolete: 'message' [C:\Users\eerhardt\source\repos\ConsoleApp119\ConsoleApp119\ConsoleApp119.csproj]
\ConsoleApp119\obj\Debug\net8.0\System.Text.Json.SourceGeneration\System.Text.Json.SourceGeneration.JsonSourceGenerator\JsonContext.MyClass.g.cs(53,36): warning EE01: 'MyClass.Name' is obsolete: 'message' [C:\Users\eerhardt\source\repos\ConsoleApp119\ConsoleApp119\ConsoleApp119.csproj]
\ConsoleApp119\obj\Debug\net8.0\System.Text.Json.SourceGeneration\System.Text.Json.SourceGeneration.JsonSourceGenerator\JsonContext.MyClass.g.cs(54,45): warning EE01: 'MyClass.Name' is obsolete: 'message' [C:\Users\eerhardt\source\repos\ConsoleApp119\ConsoleApp119\ConsoleApp119.csproj]
\ConsoleApp119\obj\Debug\net8.0\System.Text.Json.SourceGeneration\System.Text.Json.SourceGeneration.JsonSourceGenerator\JsonContext.MyClass.g.cs(80,43): warning EE01: 'MyClass.Name' is obsolete: 'message' [C:\Users\eerhardt\source\repos\ConsoleApp119\ConsoleApp119\ConsoleApp119.csproj]

Regression?

No response

Known Workarounds

globally <NoWarn> these warnings.

Configuration

No response

Other information

cc @ericstj @eiriktsarpalis @tarekgh

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Tagging subscribers to this area: @dotnet/area-system-text-json, @gregsdennis
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Tagging subscribers to this area: @dotnet/area-extensions-configuration
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[tarekgh]

@eiriktsarpalis I marked this for .NET 9.0. Let me know if you want to change that. Thanks!

[teo-tsirpanis]

Maybe Roslyn would need to add support for #pragma warning disable obsolete?

[eiriktsarpalis]

One possible approach that was considered in the past is exposing a string[] Suppressions { get; set; } property in the JsonSourceGenerationOptionsAttribute that gives users explicit control over what suppressions should be made.

[eerhardt]

exposing a string[] Suppressions { get; set; } property in the JsonSourceGenerationOptionsAttribute

One concern about that is we would need to do that for every source generator that gets/sets user defined properties. And also there are some source generators (like the ConfigurationBinder) that don't have an "Options" API where these things could be placed.

Maybe Roslyn would need to add support for #pragma warning disable obsolete?

This seems like an interesting idea. A blanket "suppress obsoletions" statement.

cc @RikkiGibson - who implemented Customizable Obsolete diagnostics (dotnet/roslyn#42518)

With other Roslyn analyzers, you can opt-in/out of running the analyzer on generated code. But since this one is built into Roslyn itself, I'm not sure how to tell it stop.

[RikkiGibson]

A pseudo-diagnostic-id similar to #pragma warning disable nullable might be the right thing here. Please file an issue on roslyn.

One rather ugly workaround here might be to put the usages of the "custom obsolete" members in an obsolete context, which does have the effect of blanket suppressing obsolete diagnostics. (seems like this also shows that compiler knows how to blanket suppress the diagnostics already.) SharpLab

using System;

public class User
{
    [Obsolete(DiagnosticId = "A")]
    public string? Prop { get; set; }
}

[Obsolete]
public class Gen {
    public void M(User user) {
        user.Prop = "B";
    }
}

[RikkiGibson]

BTW, it's also possible to disable all warnings using #pragma warning disable. But, this might be considered undesirable if it hides bugs with the generated code itself.