Compiler does no longer report local variable scope conflict

[Suchiman]

Version Used: 16.3 Preview 2

Steps to Reproduce:
I don't know if this is an expected new feature or not, i've noticed because it broke on the build server (having only 16.2.3 installed) and my .NET Framework project is set to Language version Automatically selected based on framework version (7.3).
Sharplab

using System;
using System.Collections.Generic;
using System.Linq;

public class C
{
    public List<string> Values = new List<string>();
    
    public void M(IEnumerable<C> source) 
    {
        source.Where(x => x.Values.Any(x => x == "Hello World"));
    }
}

Expected Behavior:

error CS0136: A local or parameter named 'x' cannot be declared in this scope because that name is used in an enclosing local scope to define a local or parameter

Actual Behavior:
Compiles fine

[alrz]

afaik this is a new feature in C# 8.0, local function and lambda parameters can shadow outer names.

[gafter]

If this is not documented in https://github.com/dotnet/csharplang/tree/master/proposals/csharp-8.0 then this is a (documentation) bug.

[Sliptory]

I could reproduce this error only in the project collected on .NET Core 3.0
An error is generated on the NET Framework 4.7.2.

[svick]

@Sliptory I think that's because it's a C# 8.0 feature and .Net Framework projects default to C# 7.3.

[BillWagner]

@gafter The only mention I can find for this is in #1565

I don't see a proposal doc for local static functions, which is where I would expect this.

@jcouv Does something exist that should be added?

[gafter]

@BillWagner You're right, there is no proposal document for this. The compiler/languages team has not made it a priority to maintain formal specs for the features we develop.

As best I understand the current plan, we're depending on you to provide user docs for features.

[BillWagner]

@gafter 🤣

Do you want to move this issue to dotnet/csharplang and assign it to me?

Or, if @jaredpar adds me as a contributor on this repo, just start assigning these to me.

[gafter]

There is a placeholder for a specification for this at: https://github.com/dotnet/csharplang/blob/master/proposals/csharp-8.0/shadowing-in-nested-functions.md

In short, this is by design.