Edit-and-continue changes async codegen; make it configurable

[jthorborg]

async/await and "task-like" friends is a really interesting system that actually allows to conjure a completely unmanaged stackless coroutine system, without ever involving the GC. This allows to build performant graph processing systems for games that do not suffer from recursion (and thereby stack overflow) for instance.

Unfortunately, the lowering of the feature changes codegen when running compiling under debug in an effort to support edit and continue - specifically the generated closure is a class under debug:
https://github.com/dotnet/roslyn/blob/master/src/Compilers/CSharp/Portable/Lowering/AsyncRewriter/AsyncRewriter.cs#L68

This makes it impossible to constrain generic arguments in methods in the builder pointed to by AsyncMethodBuilder to be : unmanaged.

Worse, lowering happens after proposed source generation and compilation checks before assembly is emitted, so the usual suspects like Cecil cannot be employed to solve this.

I'm working in a domain where edit and continue would never work anyway, so a reasonable compromise could be having a compiler flag for overriding whether EnC is enabled, looks like CompilationOptions was already encapsulating this perhaps with that in mind?

Thanks for any thoughts!

[bernd5]

This question seems to be belong to the roslyn repo - not csharplang.
Lowering is an implementation detail - it is not enforced by the language.

[jthorborg]

Absolutely. I seemed to have been redirected here, I started in the Roslyn repo.

[jthorborg]

Reposted in Roslyn: dotnet/roslyn#51189

This discussion can be closed now.