Configuration binder source generator emits unqualified List<T> when binding arrays without implicit usings

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
csharp
Domain
backend, build-system

Research direction

Start with gen/Emitter/CoreBindingHelpers.cs, especially EmitBindCoreImplForArray, which the issue identifies as emitting the unqualified List<T>. Build the provided reproduction with implicit usings disabled, then inspect the generated BindingExtensions.g.cs to confirm the failure. Done means array binding compiles without global using directives; also investigate why testing of #121364 missed this case.

Written by the indexing model from the issue text.

Description

area-Extensions-Configuration bug source-generator untriaged
Description

The configuration binder source generator produces code that fails to compile when binding an array with implicit usings disabled.

This is a remaining case of #118630: #121364 qualified the generated HashSet<> references, but the temporary List<> used for array binding remains unqualified.

Reproduction Steps

Create these two files and run dotnet build.

repro.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net11.0</TargetFramework>
    <ImplicitUsings>disable</ImplicitUsings>
    <EnableConfigurationBindingGenerator>true</EnableConfigurationBindingGenerator>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Configuration.Binder"
                      Version="11.0.0-rc.3.26522.148" />
  </ItemGroup>
</Project>

Program.cs

using Microsoft.Extensions.Configuration;

new ConfigurationBuilder().Build().Get<int[]>();
Expected behavior

The generated code compiles without requiring global using directives from the consuming project.

Actual behavior

The build fails:

BindingExtensions.g.cs(66,29): error CS0246: The type or namespace name 'List<>' could not be found (are you missing a using directive or an assembly reference?)

The generated array-binding method contains:

var temp1 = new List<int>();

The generated file neither imports System.Collections.Generic nor fully qualifies this type.

Regression?

Not a new .NET 11 regression. The original example also fails with Binder 8.0.0, 9.0.0, and 10.0.14, where the unqualified HashSet<> reference causes a compilation error first. The .NET 11 fix removes that error but leaves this array-binding failure.

Known Workarounds

Enable implicit usings, or add:

global using System.Collections.Generic;
Other information

EmitBindCoreImplForArray in gen/Emitter/CoreBindingHelpers.cs emits new List<...>() directly. Fully qualifying that reference would address this case.

When investigating this, also consider looking into why testing of #121364 didn't find this issue.

[!NOTE]
This issue was drafted with GitHub Copilot assistance.

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