Fix ComClassGenerator failure with generic types

[Copilot]

The ComClassGenerator fails when processing generic COM classes because hint names contain angle brackets <>, which are invalid characters for Roslyn source generators. This causes the generator to throw ArgumentException and produce no output.

[GeneratedComClass]
internal partial class ClassFactory<T> : IClassFactory where T : class, new()
{
    // Previously failed with CS8785 warning:
    // "The hintName 'ClassFactory<T>' contains an invalid character '<' at position 12."
}

Changes:

• Replace < and > with { and } in hint names when calling context.AddSource() in ComClassGenerator
• Add test coverage for generic COM class generation in ComClassGeneratorOutputShape

Original prompt

---

This section details on the original issue you should resolve

<issue_title>COM class source generator fails awkwardly with type generics</issue_title>
<issue_description>When generating a COM class with the COM source generator, the following behavior results. The warneing does indicate some issue, but it is odd it fails for both the generic and non-generic version.

The build has a warning that does indicate the problem, but the run-time behavior is rather confusing.

CSC : warning CS8785: Generator 'ComClassGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'ArgumentException' with message 'The hintName 'ClassFactory<T>' contains an invalid character '<' at position 12. (Parameter 'hintName')'.

Repro:

// > dotnet run
// CSC : warning CS8785: Generator 'ComClassGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'ArgumentException' with message 'The hintName 'ClassFactory<T>' contains an invalid character '<' at position 12. (Parameter 'hintName')'.
// Failed to query for IClassFactory: -2147467262
// Failed to query for IClassFactory: -2147467262

using System.Runtime.InteropServices;
using System.Runtime.InteropServices.Marshalling;

QueryForClassFactory(new ClassFactory());
QueryForClassFactory(new ClassFactory<object>());

static unsafe void QueryForClassFactory<T>(T t) where T : class, new()
{
    T factory = new();
    nint factoryPtr = (nint)ComInterfaceMarshaller<T>.ConvertToUnmanaged(factory);
    Guid IID_IClassFactory = typeof(IClassFactory).GUID;
    var hr = Marshal.QueryInterface(factoryPtr, in IID_IClassFactory, out nint ppvObject);
    Marshal.Release(factoryPtr);
    if (hr != 0)
    {
        Console.WriteLine($"Failed to query for IClassFactory: {hr}");
        return;
    }

    Console.WriteLine("Successfully queried for IClassFactory.");
    Marshal.Release(ppvObject);
}

[GeneratedComInterface]
[Guid("00000001-0000-0000-C000-000000000046")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
internal partial interface IClassFactory
{
    void CreateInstance(
        [MarshalAs(UnmanagedType.Interface)] object? pUnkOuter,
        ref Guid riid,
        out IntPtr ppvObject);

    void LockServer([MarshalAs(UnmanagedType.Bool)] bool fLock);
}

[GeneratedComClass]
internal partial class ClassFactory : IClassFactory
{
   public unsafe void CreateInstance([MarshalAs(UnmanagedType.Interface)] object? pUnkOuter, ref Guid riid, out nint ppvObject)
    => throw new NotImplementedException();

   public void LockServer([MarshalAs(UnmanagedType.Bool)] bool fLock)
    => throw new NotImplementedException();
}

[GeneratedComClass]
internal partial class ClassFactory<T> : IClassFactory where T : class, new()
{
   public unsafe void CreateInstance([MarshalAs(UnmanagedType.Interface)] object? pUnkOuter, ref Guid riid, out nint ppvObject)
    => throw new NotImplementedException();

   public void LockServer([MarshalAs(UnmanagedType.Bool)] bool fLock)
    => throw new NotImplementedException();
}
```</issue_description>

<agent_instructions>To fix this issue, update the `ComClassGenerator` to replace `<` and `>` with `{` and `}` when producing hint names for the generated source files.

Also, add a test case to validate that we don't regress the behavior in the future.</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
<comment_new><author>@AaronRobinsonMSFT</author><body>
/cc @jkoritzinsky @jtschuster </body></comment_new>
</comments>

• Fixes COM class source generator fails awkwardly with type generics #122191

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[AaronRobinsonMSFT]

[Copilot]

Pull request overview

This PR fixes a bug where the ComClassGenerator source generator fails when processing generic COM classes. The issue occurs because Roslyn's AddSource() method rejects hint names containing angle brackets (<, >), which are present in generic type names like ClassFactory<T>. The fix replaces these characters with curly braces ({, }) to create valid hint names while preserving uniqueness.

Key Changes

• Modified hint name generation in ComClassGenerator to replace invalid angle bracket characters
• Added test coverage for generic COM class generation

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
ComClassGenerator.cs	Replaces < and > with { and } in hint names before calling AddSource()
ComClassGeneratorOutputShape.cs	Adds test case to verify generic COM class generation works correctly

[jkoritzinsky]

/ba-g failures tracked by #122228