fix issues 14591, 17310: ambiguous mangling for calling conventions Pascal and Objective-C

[rainers]

This changes mangling of extern(Pascal) to "Np" and extern(Objective-C) to "No".

There is no support for Objective-C in druntime or phobos, but Pascal needs a few changes: dlang/druntime#1812 and dlang/phobos#5333

[dlang-bot]

Fix	Bugzilla	Description
✓	14591	[SPEC] Ambiguity between extern(Pascal) and template value parameters
✓	17310	[SPEC] Ambiguous mangling for 'Y', Objective-C function or variadic arguments?

[ibuclaw]

Bang on time just as I'm about to send patches for gcc to remove the pascal specific special case for a more generic approach. ☺️

[ibuclaw]

My initial thoughts are not so sure about using N for a third meaning. There's already special handling between the two existing uses of N.

[rainers]

My initial thoughts are not so sure about using N for a third meaning. There's already special handling between the two existing uses of N.

Yeah, but the other extendible encoding is 'z' which seems to be no better.

An alternative would be to extend this change to the extern(Windows) mangling and then use 'Ww', 'Wp' and 'Wo'.
Edit: extern(C++) and maybe even extern(C) could be added aswell

[rainers]

My initial thoughts are not so sure about using N for a third meaning.

An alternative would be to extend this change to the extern(Windows) mangling and then use 'Ww', 'Wp' and 'Wo'.

Another option could be to always use 'F' for function types of any linkage, and then use Np, etc. as a modifier for linkage other than extern(D).
Please note that this doesn't affect functions themself (they provide their own C/C++/Pascal mangling), but only declarations using their function type.

AFAICT all remaining demangle failures in dlang/druntime#1830 (comment) are caused by this ambiguity.

[rainers]

Another option could be to always use 'F' for function types of any linkage, and then use Np, etc. as a modifier for linkage other than extern(D).

We could also just prefix all the non-D calling convention letters 'U','W','V','R','Y' with 'F' as a function cannot directly follow as an argument. This wouldn't "release" those characters for other encodings, though.

[Geod24]

What's the status of this ? I saw some effort from @ibuclaw to deprecate Pascal calling convention (#4658). Can we close this and move forward with deprecation instead ?

[rainers]

Can we close this and move forward with deprecation instead ?

extern(Pascal) is still used in a couple of Windows header files, e.g. core.sys.windows.mapi and core.sys.windows.httpext.

[thewilsonator]

extern(Pascal) has been deprecated. Close this?

[rainers]

Fine with me.