[Dlang-internal] DIP1000 discussion and testing

[Martin Nowak via Dlang-internal]

On Monday, 24 October 2016 at 09:13:58 UTC, Mathias Lang wrote:
> void* escape3 (scope void* p) @safe
> {
>     Escaper e;
>     scope dg = () { return e.e; };
>     e.e = p;
>     return dg();
> }

Seems like this would require that the scope tainting is done in 
a separate pass, before going through the statements in lexical 
order. The dg needs to know that e will escape in order to change 
to return scope.
Not sure the compiler is ready for 2-pass function semantics.
While it's clearly powerful, my intuition also goes a bit against 
it.
- Does the compiler architecture allow for the necessary 
semantics.
- What's a use-case that requires this?
- Might the scope inference graph have cycles?
- Can humans understand scope inference, and can we print proper 
error messages?

It might be a bit too ambituous, and turn out to be an unforced 
error creating too many scope holes.