[C++ RFC/Patch] PR 34938

[Jason Merrill]

On 08/22/2014 01:53 PM, Paolo Carlini wrote:
> maybe this old issue is already fixed. We used to ICE on:
>
> typedef void (*fptr)() __attribute((noreturn));
> template<int> void foo();
> template<fptr> void bar();
>
> fptr f = bar< foo<0> >;
>
> but lately we simply reject it:
>
> 34938.C:5:10: error: no matches converting function ‘bar’ to type ‘fptr
> {aka void (*)() volatile}’
> fptr f = bar< foo<0> >;
> ^
> 34938.C:3:21: note: candidate is: template<void (* <anonymous>)()
> volatile> void bar()
> template<fptr> void bar();
> ^
>
> is that Ok? clang behaves like us, EDG accepts the code.

Well, since the attribute is outside the language, I guess we get to 
decide what it means; C++11 [[noreturn]] is only defined on decls, not 
types.

I think rejecting it makes sense; since bar is not declared as noreturn, 
assigning its address to a noreturn function pointer seems wrong.

> A secondary
> issue I noticed is that we print 'volatile' instead of the attribute,
> that is fixed by the patchlet below.

Currently function-cv-quals on a FUNCTION_TYPE used as a typedef or 
template parameter have the same encoding as the const and noreturn 
attributes; to get the printing right you need to know the context of 
the FUNCTION_TYPE.  If it's the type of a pointer, then the attribute is 
correct.

Jason