https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106793
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2022-09-01
Keywords| |diagnostic
Resolution|INVALID |---
Summary|std::barrier missing |poor diagnostic for missing
|default template argument? |template argument list on
| |function parameter
Status|RESOLVED |NEW
Ever confirmed|0 |1
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reopening as a diagnostic bug.
With an unnamed parameter like so:
template<class T = void> struct barrier { };
void func(barrier&) { }
G++ says:
param.C:3:11: error: class template placeholder ‘barrier’ not permitted in this
context
3 | void func(barrier&) { }
| ^~~~~~~
With a named parameter like so:
template<class T = void> struct barrier { };
void func(barrier& b) { }
G++ says:
param.C:3:11: error: template placeholder type ‘barrier<...auto...>’ must be
followed by a simple declarator-id
3 | void func(barrier& b) { }
| ^~~~~~~
param.C:1:33: note: ‘template<class T> struct barrier’ declared here
1 | template<class T = void> struct barrier { };
| ^~~~~~~
Neither of these are really useful. This is not a template placeholder type,
it's just an invalid attempt to refer to barrier<>&.
If we hit this error, could we look up 'barrier' and see what it is? If it's a
concept, give the template placeholder type error, and if it's a class template
suggest that the template argument list is missing. For bonus points, if the
class template can be instantiated with an empty template argument list, add a
fix-it suggesting '<>'
