VSMEF015 Metadata view interface should be source-generated

VSMEF015 warns when a C# import uses a metadata view interface declared in the same compilation, but that interface is not set up for VS MEF source generation.

Why this matters

Without source generation, VS MEF falls back to the older runtime-generated metadata view path. If you own the interface, source generation is the simpler and more predictable option.

How to fix it

Annotate the interface with MetadataViewAttribute and declare it partial.

using Microsoft.VisualStudio.Composition;

[MetadataView]
public partial interface IMyMetadata
{
    string Name { get; }
}

If the interface is nested, each containing type must also be partial.