> IMO your opinion is self-contradictory. On the one hand you say that mangling is depend on back-end and should be calculated in back-end. On the other hand, you want to introduce common limitation for all platforms.

You should stop trying to read between the subtext, as there is none here.  I have no idea where you are coming from in assuming that was my intention.

> Current mangle check is generally meaningless.

It is meaningless, why should the frontend care about what mangling is applied to the symbol?

> Ergo: pragma(mangle) should allow any mangle and pass it to check to glue/back-end.

It perhaps should, but that doesn't mean you should test for it using the most ridiculous examples in the testsuite.

> Moreover, this changing allow me to write good postcondition to Declaration::mangle function.

This postcondition is only ran in dmd/win32.  So if lets say we come to agree that pragma(mangle) should be left unchecked (apart from some common things - such as zero length string) then this routine being here is useless, and better off being a static in mangle.c