Tagging @dotnet/roslyn-ide @Pilchie .

Note: this fixes all of the cases from #22672 except for this one:

using System;

class Enclosing<T>
{
    delegate T MyDelegate(T t);
    static void Callee(MyDelegate d) => d(default);

    public class Class<T>
    {
        public void Caller()
        {
            MyDelegate local = x => x;
            Callee(local);
        }
    }
}

We will still offer the feature here, which will produce the broken code:

using System;

class Enclosing<T>
{
    delegate T MyDelegate(T t);
    static void Callee(MyDelegate d) => d(default);

    public class Class<T>
    {
        public void Caller()
        {
            T local(T x) => x;
            Callee(local);
        }
    }
}

The reason this is broken is that local is now referencing hte T type parameter from the containing class Class<T>, whereas before it was using hte T type parameter from Enclosing<T>. This breaks because, of course, there's no language facility to reference a specific type parameter with the same name (unlike with types, when you can do things like global::)

The reason i didn't fix this was that it seemed like a pretty unlikely case. Reusing the same type parameter name is highly discouraged in C# (the compiler even reports a warning for this). As such, most people will gives these non conflicting names, and the change will be fine.

If this is felt to be important enough to fix, it will take medium effort to fix. Specifically, the analysis code will have to see which type parameters were captured in the parameter and return type of the lambda. It will then have to see if, from the replacement location, the names of those type parameters bind back to that type parameter and not to some other type in scope (like another nested type, or a method/class type parameter, etc.).

@chborl Kevin asked me to look at #23118. IN the process of doing so, i ended up addressing most of the cases of #22672 since it was all in the exact same code location. I hope that's ok!

If this is felt to be important enough to fix

Let's just file this as a follow-up bug.

@CyrusNajmabadi Let me know when you have seen the feedback above and I'll move it forward after you are done with any changes you wanted to make.

Have made the code change. Feel free to do what you want now :)

Thanks, @CyrusNajmabadi :)

Any time!