InsertMembers with method declarations to an interface declaration causes modifiers to be reset

[hugener]

Version Used: 4.4.0

Steps to Reproduce:

1. In an analyzer codefix, I use the SyntaxFactory.MethodDeclaration to create a method declaration with public, static modifiers and an implementation to leverage default interface methods. (https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/default-interface-methods)
2. Insert methods into an interface declaration with SyntaxGenerator.InsertMembers
3. The methods are added, but the public and static modifiers are stripped from the SyntaxTree giving a different meaning to the generated code.

Sorry I did create a minimal solution, but I found the line that I suspect causes modifiers to be stripped in case of adding to an interface declaration:

roslyn/src/Workspaces/CSharp/Portable/CodeGeneration/CSharpSyntaxGenerator.cs

Line 775 in b1b8636

.WithModifiers(default)

I can understand the behavior, in the context of C# not supporting this prior to version 8, but shouldn't this be a supported scenario now?

Does anyone see a workaround?

Expected Behavior:

Code to be generated as:

public interface IOption<T>
{
    public static IOption<T> Some(T value) => new Some<T>(value);
}

Actual Behavior:

public interface IOption<T>
{
    IOption<T> Some(T value) => new Some<T>(value);
}

[jaredpar]

I can understand the behavior, in the context of C# not supporting this prior to version 8, but shouldn't this be a supported scenario now?

The other consideration is whether or not changing the behavior will impact existing use cases. Have to consider existing customers may be depending on this behavior. Not sure that we can safely change this.

@333fred to confirm

[333fred]

This is an IDE api. Moving over there for triage.