`Command` class violates design rule CA1010

[smdn]

Summary

The System.CommandLine.Command class implements non-generic IEnumerable, but it does not implement IEnumerable<T>.

command-line-api/src/System.CommandLine/Command.cs

Line 25 in cf5fd8d

public class Command : Symbol, IEnumerable

This causes classes inheriting from the Command class to violate design rule CA1010.
For projects with AnalysisMode set to Recommended or All, warning CA1010 will occur.

Build succeeded.

/home/smdn/temp/cli/Lib.cs(5,14): warning CA1010: Type 'MyCommand' directly or indirectly inherits 'IEnumerable' without implementing 'IEnumerable<T>'. Publicly-visible types should implement the generic version to broaden usability. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1010) [/home/smdn/temp/cli/cli.csproj]
    1 Warning(s)
    0 Error(s)

This simply triggers a warning and does not corrupt any functionality of System.CommandLine.
However, since the cause of the warning is not easy to find out and it may cause confusion, so I think this should be fixed.

Steps to reproduce

Set AnalysisMode to Recommended or All in the csproj file.

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

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net10.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>

    <!-- Enable design rules including CA1010 -->
    <AnalysisMode>Recommended</AnalysisMode>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="System.CommandLine" Version="2.0.1" />
  </ItemGroup>

</Project>

Create a class that inherits from the Command class.

using System.CommandLine;

namespace MyLibrary;

// warning CA1010: Type 'MyCommand' directly or indirectly inherits 'IEnumerable' without implementing 'IEnumerable<T>'. Publicly-visible types should implement the generic version to broaden usability. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1010)
public class MyCommand(string name, string? description) : Command(name, description) { }

Workarounds

The following workarounds are available to avoid this warning.

Workaround 1: disable warning CA1010

#pragma warning disable CA1010
public class MyCommand(string name, string? description) : Command(name, description)
{
}
#pragma warning restore CA1010

Workaround 2: implement IEnumerator<Symbol>

public class MyCommand(string name, string? description) : Command(name, description)
{
    // Implement IEnumerator<Symbol> in order to suppress warning CA1010.
    public IEnumerator<Symbol> GetEnumerator() => Children.GetEnumerator();
}

Workaround 3: reduce AnalysisMode

    <!-- Reduce `AnalysisMode` to either `None`, `Default`, or `Minimum`. -->
    <AnalysisMode>Minimum</AnalysisMode>

[KalleOlaviNiemitalo]

The comment here says that the IEnumerable.GetEnumerator implementation in Command exists only to enable collection initializers in C# and isn't meant to be called:

https://github.com/dotnet/dotnet/blob/b0f34d51fccc69fd334253924abd8d6853fad7aa/src/command-line-api/src/System.CommandLine/Command.cs#L237-L240

As such, adding IEnumerable<Symbol> to Command feels wrong. Instead, the System.CommandLine package could ship a DiagnosticSuppressor that suppresses CA1010 in classes that are derived from Command and don't otherwise implement IEnumerable.