[cxx-abi-dev] mangling of vendor extension, expression on function (not function type)

[John McCall]

On Jan 20, 2014, at 6:13 PM, Nick Lewycky <nlewycky at google.com> wrote:
> I'm trying to mangle a vendor extension that encodes an expression which applies to function overload candidates, with the goal that a user running the demangler would see their expression demangled. While there are various vendor extension points, none of them allow me to go into encoding an expression, unless I stick a stray "decltype" in there, or similar (expression in a template argument that doesn't actually exist, etc.).
> 
> The vendor extension is described in full here: http://clang.llvm.org/docs/LanguageExtensions.html#controlling-overload-resolution .
> 
> I don't think I can do it without an extension to the mangling rules. As a strawman proposal, I suggest this:
> 
> <type> ::= Ue <expression> E # vendor extended type qualifier

I think you mean

  <type> ::= Ue <source-name> <expression> E <type>

And this would be valuable for mangling e.g. dependent address space qualifiers, if anybody ever wants to do those.

However, it feels really forced to add your feature, specifically, to <type>, since it can’t appear in an arbitrary position; it’s much closer to a qualified method name.  But the ref/cv-qualifiers area is only allowed in a <nested-name>, and you need to be able to do this on a top-level function, so I suppose extending <type> in a known-useful direction and then abusing <type> might be the best thing.

On the other hand, isn’t this a proposed direction for standardization?  I would have no problem with giving this a proper, non-vendor mangling just in case.

John.