[cfe-dev] [PATCH] Using private types should be allowed as template parametter for explicit instantiation

[Olivier Goffart]

Le Tuesday 22 June 2010, John McCall a écrit :
> On Jun 22, 2010, at 11:39 AM, Olivier Goffart wrote:
> > On Thursday 17 June 2010, Olivier Goffart wrote :
> >> Hello.
> >> 
> >> Attached you will find my attempt to fix
> >> http://llvm.org/bugs/show_bug.cgi?id=7267
> >> 
> >> The problem is that in this code
> >> 
> >> class X { class Y; };
> >> template<class T> struct Test {};
> >> template<> struct Test<X::Y> {};
> >> 
> >> Clang would complains that X::Y is private.
> >> 
> >> While the C++ specification 14.7.2 [temp.explicit] p11
> >> says it should compile (The usual access checking rules do not apply to
> >> names used to specify explicit instantiations)
> >> 
> >> (This break compilation of Qt's linguist tool)
> >> 
> >> 
> >> The patch is only one line but was not trivial.
> >> By having a ParsingDeclRAIIObject while parsing that kind of close, we
> >> make sure any diagnostic are delayed. And because I do not call
> >> complete() on it, the delayed diagnostic will not be issued.
> >> 
> >> Does my patch makes sens this time?
> >> 
> >> Regards.
> > 
> > Ping?
> 
> Sorry, missed this the last time.  This patch won't work for several
> reasons.
> 
> 1.  You're suppressing access checks whenever
> ParseTemplateIdAfterTemplateName parses a template argument list.  That's
> actually a large number of cases, most of which are not explicit
> instantiations.  It happens to be the case that certain very common cases
> follow a different code path, which is why your test case works, but there
> are many other cases where this breaks things.

Would you have examples of that?

> 
> 2.  You're suppressing access checks for explicit specializations, not just
> explicit instantiations.  I see no justification of that in the standard.

I  see explicit specializations as a special case of explicit instantiations

This is specially the case I have error with.
How else do you define traits for private types?

All the other compilers support that. And even clang already support it 
already for function explicit specializations, only the class is missing.

> 3.  You're only suppressing access checks in the template arguments, not in
> the template name itself (it could be a private member template) or in the
> associated types (if it's a function template).  *All* access checks in
> the declaration need to be suppressed.

Function parameters case is taken elsewhere; (it already works for functions.) 


> 4.  The use of ParsingDeclRAIIObject is clever, but I suspect it won't work
> as desired for explicit instantiations of function templates.

It work with function template and this is why i used it there.