https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115915
Bug ID: 115915
Summary: gcc fails to detect invalid friend declaration of
classes in different namespaces
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Keywords: accepts-invalid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: rush102333 at gmail dot com
Target Milestone: ---
Please take a look at the following code:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
namespace std_1 {
template<class> struct extent{};
}
using namespace std_1;
struct S {
friend class extent;
};
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The statement "friend class extent" in line 9 is syntactically invalid. Because
"extent" is a template class, the template argument value of this class must be
specified when it is declared as a friend class of other classes. For example,
"friend class extent<int>".
However, GCC seems to ignore that rule and accept the code. This only happens
when "extent" is declared in an independent namespace. Clang rejects that code
by giving the following message:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<source>:9:23: error: template 'extent' cannot be referenced with the 'class'
specifier
9 | friend class extent;};
| ^
<source>:2:28: note: declared here
2 | template<class> struct extent;
| ^
1 error generated.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
MSVC also rejects the code, but EDG and ICC seem to accept it.
https://godbolt.org/z/xMbvaf768
Without namespace:
https://godbolt.org/z/evdEWaqT7
