Roslyn: Proposal: non-removable 'using' operator

[WrongBit]

When you use VS help on removing unused 'using's, some of 'em should not be removed, because they are used in a different configuration (RELESE, DEBUG, etc), but not needed in current one.
I suggest some mark for such using 'never remove it!'. Suggestions:

using Abc.Def;// KEEP!

[Keep]using Abc.Def;

using! Abc.Def;

We have many variants.
OFFTOP: usings are such a clumsy idea! Why they are not kept at project level? Why they are needed in every single file? (I speak not about ambiguous cases)

[eyalsk]

@WrongBit From the language's standpoint using preprocessor directives should be more than enough to address this case.

[huoyaoyuan]

using System;
#if DEBUG
using Abc.Def;
#endif 

Currently, analyzer and compiler see each configuration separately. Putting the using into #if will let it ignored in other configurations.

[yaakov-h]

You may also be able to surround it with #warning disable or similar.

[333fred]

This is not a language request. Transferring to roslyn.

[CyrusNajmabadi]

Why they are needed in every single file? (I speak not about ambiguous cases)

Because then your code changes meaning based on config settings to your compiler.

[jinujoseph]

Duplicate of #24084