Roslyn: C# Interactive allows illegal shadowing within a single statement

[aluanhaddad]

Version Used:
Visual C# 2017 RC 00369-50000-00000-AA881
Steps to Reproduce:

1. Open the C# Interactive Window and enter
   C# var task = Task.Run(() => 1).ContinueWith(task => task.Result);

Expected Behavior
An error is reported

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

Actual Behavior:
The code compiles and executes.

[gafter]

This may not be a bug; the "enclosing" symbol is a field, not a local.

[jnm2]

This may not be a bug; the "enclosing" symbol is a field, not a local.

Something about this bothers me deeply. As far as the C# scripting language spec is concerned, that should stay an implementation detail, shouldn't it?

[tmat]

Yes, the fact that the script variable is backed by a field is an implementation detail. However, we may chose to allow this shadowing. Note that the C# scripting language spec doesn't exist yet.

[jnm2]

Note that the C# scripting language spec doesn't exist yet.

Which is why I brought it up- since we're deviating from the C# language a bit, we will want one 😄

[aluanhaddad]

Also, the scripting language interfaces directly with Visual Studio projects and there are commands like send to interactive. It would be best for the language semantics to be as 1 to 1 as possible