https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85604
Bug ID: 85604
Summary: Default template arguments in friend class template
declarations should not be allowed
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: adr26__gcc at nunsway dot co.uk
Target Milestone: ---
template <int A, bool L> struct Template_Class;
struct Other_Struct
{
template <int A, bool L = (A < 42)> friend struct Template_Class;
};
template <int A, bool>
struct Template_Class
{
};
template <>
struct Template_Class<0>
{
};
Per [temp.param]/12:
"A default template-argument shall not be specified in a friend class template
declaration."
All versions of G++ since at least 4.1.2 accept the code above.
Clang++ correctly rejects this code:
<source>:5:26: error: default template argument not permitted on a friend
template
template <int A, bool L = (A < 42)> friend struct Template_Class;
^ ~~~~~~~~
<source>:14:8: error: too few template arguments for class template
'Template_Class'
struct Template_Class<0>
^
<source>:9:8: note: template is declared here
struct Template_Class
^
https://godbolt.org/g/Tvf7Fr
