http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47342
Summary: misleading diagnostic for member of undeclared class
template partial specialization
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: enhancement
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: r...@gcc.gnu.org
g++ does not distinguish between invalid uses of an incomplete partial
specialization and an undeclared partial specialization:
template<class T>
struct X : T
{
void f();
};
template<class T>
inline void
X<T>::f()
{ }
template<typename T>
struct Y
{ };
#ifdef CORRECT
template<class T>
struct X< Y<T> > : Y<T>
{
void f();
};
#endif
template<class T>
inline void
X< Y<T> >::f() // xxx
{ }
$ g++ ps.cc
ps.cc:26: error: invalid use of incomplete type 'struct X<Y<T> >'
ps.cc:3: error: declaration of 'struct X<Y<T> >'
The diagnostic is rather unhelpful.
The problem is not that the type is incomplete, but that there is not even a
declaration of the class template partial specialization X<Y<T>> (which can be
fixed by defining CORRECT). The second error referring to line 3 is wrong,
that's the declaration of the primary template, not the partial specialization.
The diagnostic would be almost correct (apart from the line number) if the
class template partial specialization had been declared but not defined, like
so
template<class T> struct X< Y<T> >;
but that is not the case here.
This is a regression since 4.1 which correctly states the type is undefined,
not incomplete:
ps.cc:27: error: invalid use of undefined type `struct X<Y<T> >'
ps.cc:3: error: declaration of `struct X<Y<T> >'
ps.cc:27: error: template definition of non-template `void X<Y<T> >::f()'
EDG gives:
"ComeauTest.c", line 26: error: template argument list must match the parameter
list
X< Y<T> >::f() // xxx
^
This isn't very informative but is more accurate, referring to the wording in
[temp.class.spec.mfunc]p1:
The template argument list of a member of a class template partial
specialization shall match the template argument list of the class template
partial specialization.
Clang++ gives a more helpful diagnostic:
ps.cc:26:14: error: nested name specifier 'X<Y<T> >::' for declaration does not
refer into a class, class template or class template partial
specialization
X< Y<T> >::f() // xxx
~~~~~~~~~~~^
1 error generated.
Sun CC gives arguably the best diagnostic:
"ps.cc", line 27: Error: Could not find partial specialization matching
X<Y<T>>.
1 Error(s) detected.
(N.B. clang++ gives a worse diagnostic for the case where the class template
partial specialization has been declared but not defined and CC accepts it
without error)
