ConfigurationBinder source generator generates code with the wrong nullable annotations

[eerhardt]

Description

When attempting to use the ConfigurationBinder source generator in dotnet/extensions (see dotnet/extensions#4625), I'm getting a nullable warning that is causing the generated code to not compile (I would need to disable nullable validation for the whole project if I wanted to ignore the nullable warning, which isn't acceptable).

I'm not sure what the general pattern is here that causes this issue, so I logged the issue for the scenario specifically. I think it might need to include nested generics where one of the nested generic types is nullable.

Reproduction Steps

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

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <EnableConfigurationBindingGenerator>true</EnableConfigurationBindingGenerator>
    <NoWarn>$(NoWarn);SYSLIB1100;SYSLIB1101</NoWarn>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="8.0.0-rtm.23511.16" />
    <PackageReference Include="Microsoft.Extensions.Http.Resilience" Version="8.0.0-rc.2.23510.2" />
  </ItemGroup>

</Project>

// needed to work around https://github.com/dotnet/runtime/issues/94065
global using Polly;
global using Polly.Hedging;
global using Polly.RateLimiting;
global using Polly.Timeout;

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Http.Resilience;

var c = new ConfigurationBuilder().Build();
c.Get<HttpStandardHedgingResilienceOptions>();

Expected behavior

Should be without warnings

Actual behavior

Get a nullable warning from generated code:

CS8619	Nullability of reference types in value of type 'Func<HedgingActionGeneratorArguments<HttpResponseMessage>, Func<ValueTask<Outcome<HttpResponseMessage>>>?>' doesn't match target type 'Func<HedgingActionGeneratorArguments<HttpResponseMessage>, Func<ValueTask<Outcome<HttpResponseMessage>>>>'.	ConsoleApp101	C:\Users\eerhardt\source\repos\ConsoleApp101\ConsoleApp101\Microsoft.Extensions.Configuration.Binder.SourceGeneration\Microsoft.Extensions.Configuration.Binder.SourceGeneration.ConfigurationBindingGenerator\BindingExtensions.g.cs	1418		

The generated code looks like:

            if (AsConfigWithChildren(configuration.GetSection("ActionGenerator")) is IConfigurationSection section256)
            {
                Func<HedgingActionGeneratorArguments<HttpResponseMessage>, Func<ValueTask<Outcome<HttpResponseMessage>>>>? temp258 = instance.ActionGenerator;
                if (temp258 is not null)
                {

That middle line is the issue, it is of type:

Func<HedgingActionGeneratorArguments<HttpResponseMessage>, Func<ValueTask<Outcome<HttpResponseMessage>>>>
but the type of instance.ActionGenerator is:
Func<HedgingActionGeneratorArguments<TResult>, Func<ValueTask<Outcome<TResult>>>?>

Note the ? inside the last > brace.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

cc @tarekgh @ericstj

[ghost]

Tagging subscribers to this area: @dotnet/area-extensions-configuration
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

When attempting to use the ConfigurationBinder source generator in dotnet/extensions (see dotnet/extensions#4625), I'm getting a nullable warning that is causing the generated code to not compile (I would need to disable nullable validation for the whole project if I wanted to ignore the nullable warning, which isn't acceptable).

I'm not sure what the general pattern is here that causes this issue, so I logged the issue for the scenario specifically. I think it might need to include nested generics where one of the nested generic types is nullable.

Reproduction Steps

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

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <EnableConfigurationBindingGenerator>true</EnableConfigurationBindingGenerator>
    <NoWarn>$(NoWarn);SYSLIB1100;SYSLIB1101</NoWarn>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="8.0.0-rtm.23511.16" />
    <PackageReference Include="Microsoft.Extensions.Http.Resilience" Version="8.0.0-rc.2.23510.2" />
  </ItemGroup>

</Project>

// needed to work around https://github.com/dotnet/runtime/issues/94065
global using Polly;
global using Polly.Hedging;
global using Polly.RateLimiting;
global using Polly.Timeout;

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Http.Resilience;

var c = new ConfigurationBuilder().Build();
c.Get<HttpStandardHedgingResilienceOptions>();

Expected behavior

Should be without warnings

Actual behavior

Get a nullable warning from generated code:

CS8619	Nullability of reference types in value of type 'Func<HedgingActionGeneratorArguments<HttpResponseMessage>, Func<ValueTask<Outcome<HttpResponseMessage>>>?>' doesn't match target type 'Func<HedgingActionGeneratorArguments<HttpResponseMessage>, Func<ValueTask<Outcome<HttpResponseMessage>>>>'.	ConsoleApp101	C:\Users\eerhardt\source\repos\ConsoleApp101\ConsoleApp101\Microsoft.Extensions.Configuration.Binder.SourceGeneration\Microsoft.Extensions.Configuration.Binder.SourceGeneration.ConfigurationBindingGenerator\BindingExtensions.g.cs	1418		

The generated code looks like:

            if (AsConfigWithChildren(configuration.GetSection("ActionGenerator")) is IConfigurationSection section256)
            {
                Func<HedgingActionGeneratorArguments<HttpResponseMessage>, Func<ValueTask<Outcome<HttpResponseMessage>>>>? temp258 = instance.ActionGenerator;
                if (temp258 is not null)
                {

That middle line is the issue, it is of type:

Func<HedgingActionGeneratorArguments<HttpResponseMessage>, Func<ValueTask<Outcome<HttpResponseMessage>>>>
but the type of instance.ActionGenerator is:
Func<HedgingActionGeneratorArguments<TResult>, Func<ValueTask<Outcome<TResult>>>?>

Note the ? inside the last > brace.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

cc @tarekgh @ericstj

Author:	eerhardt
Assignees:	-
Labels:	area-Extensions-Configuration
Milestone:	-

[eiriktsarpalis]

That's surprising, doesn't the generated code suppress nullability warnings in source?

[eerhardt]

That's surprising, doesn't the generated code suppress nullability warnings in source?

No, it explicitly enables it:

runtime/src/libraries/Microsoft.Extensions.Configuration.Binder/gen/ConfigurationBindingGenerator.Emitter.cs

Lines 39 to 43 in 44a5abd

	_writer.WriteLine("""
	// <auto-generated/>
	#nullable enable
	#pragma warning disable CS0612, CS0618 // Suppress warnings about [Obsolete] member usage in generated code.
	""");

[eiriktsarpalis]

That seems surprising given that this was picked up from the JSON generator:

runtime/src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs

Lines 136 to 145 in c1f4341

	writer.WriteLine("""
	// <auto-generated/>
	#nullable enable annotations
	#nullable disable warnings
	// Suppress warnings about [Obsolete] member usage in generated code.
	#pragma warning disable CS0612, CS0618
	""");

I think we should consistently disable nullability warnings in all generated code (except perhaps in debug builds of the generator?)

[eiriktsarpalis]

@eerhardt I'm preparing a PR that disables nullability warnings in generated code. I'm not super familiar with this library though, do you know if there's a minimal repro I can use that doesn't require the dependency on Polly?

[eerhardt]

Unfortunately, no I don't. I haven't had time to pare it down.

I would try making a type of Func<HedgingActionGeneratorArguments<TResult>, Func<ValueTask<Outcome<TResult>>>?>

where HedgingActionGeneratorArguments and Outcome are generic types.

[eiriktsarpalis]

Is that warning a side-effect of the generator erroneously generating binding code for delegate types?

[eerhardt]

Yes, but I believe the issue will also occur if you replace the Func with some other generic types.

[eiriktsarpalis]

This was addressed in .NET 8 via #94267 by disabling nullability warnings altogether. Moving to Future for a fix that addresses the specific annotation issue.

[eiriktsarpalis]

Moving to 10.0.0