>So that is _Z4bar1v and not __Z4bar1v as some platforms may add the extra underscore implicitly. :)

Yes, of course.:) BTW this behaviour was introduced long before my pull.

Anyway, hard mangling (like C++) should be constructed in front-end, because front-end should define D types mapping to other language. We was have any troubles when C++ mangling was constructed in backend (or glue). And if mangle is builded in front-end, we can return it from `.mangleof`. And I think, we should do it. (I was wrote arguments early.) For simple mangling "like C, Pascal, Stdcall", we can build it in front-end without any efforts. Now I work correctly and we will not any troubles with supporting it (As I see)
I think, the main thing is that all mangling done in single point. 

>try to (incorrectly) implement this

I've moved _all_ mangling to front-end. Now compiler always pass to back-end _mangled_ symbol.
Now all works correctly.
May be I don't see some pitfalls in this way? Please point to it. 
Suppose, we've approved this pull. What problems, do you think, we face now? After year? After 10 years?
What problems faced user?
You see that this way incorrect. But I don't see any troubles. I understand that I may miss something. But you don't say about any (potential) concrete trouble. All your objections are conceptual in nature. May be you don't like something by force of habit?