https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118382
Bug ID: 118382
Summary: GCC fails to detect erroneous implicit template
argument specification in extern class declaration for
template class with default argument
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wangbopku15 at gmail dot com
Target Milestone: ---
The following code seems to have some problems:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
template <typename=int>
struct D{};
extern D d;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In a template class declaration(not definition), the template arguments must be
explicitly specified, which means the '<>' specifier should not be eliminated
here. The correct version might be like:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
template <typename=int>
struct D{};
extern D<> d;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
EDG, Clang, and ICC reject the first one and accept the second, but GCC seems
to accept both:
https://godbolt.org/z/55b1vrrP5
