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Command class violates design rule CA1010 #2751
Description
Summary
The System.CommandLine.Command class implements non-generic IEnumerable, but it does not implement IEnumerable<T>.
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 CA1010Workaround 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>
Activity
KalleOlaviNiemitalo commentedon Dec 30, 2025
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.