Multiple alias this redux

[Andrei Alexandrescu via Digitalmars-d]

Following the approval of his DIP66, Igor Stepanov proceeded with an 
implementation at https://github.com/D-Programming-Language/dmd/pull/3998.

Walter and I objected that the implementation is overly complex. My 
opinion is much weaker than his; I'm not deeply familiar with the dmd 
internals. Iain Buclaw seems to agree with Walter. and Igor has replied 
with additional explanations for the added complexity.

As a result:

* We have no alias this

* The compiler is 2 KLOC smaller/simpler

* The PR has bitrotten

* Igor is probably frustrated

So this is a stalemate that I'd like to see broken. The best solution I 
see with this is a core compiler contributor reviewing Igor's code and 
either:

(a) Assuming Igor is still interested, give concrete, actionable 
guidance to Igor so he can simplify the PR and follow through 
shepherding the PR into dmd;

(b) If Igor is no longer interested, either take over the PR and modify 
it for approval, or implement DIP66 from first principles;

(c) Review the code and discussion, and reach the conclusion the 
proposed implementation is appropriate and no radical simplifications 
are within reach.

Please chime in if you'd like to take this over.


Thanks,

Andrei