https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102042
Bug ID: 102042
Summary: specialization after instantiation error possibly
rooted from mis-calculating template function
signature of parameter of array of template function
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: nickhuang99 at hotmail dot com
Target Milestone: ---
I suspect this is from similar root cause of PR101402, PR102033, PR102034 etc.
when incorrectly dropping top-level cv-qualifier during calculating template
function declarator of which parameter is an array of template function
pointer.
Clearly from "#2" of static assert, GCC already gets correct specialization
"g<1,int>" signature, still the last statement of specialization declaration
causes error with very strange error message.
clang(https://www.godbolt.org/z/5eM5b4GjG) accepts.
MSVC++(https://www.godbolt.org/z/3x9dvsfTh) stumbles like GCC, but a better
clear clue.
#include<type_traits>
template<unsigned int N, class T>
void f(const T[N]){}
template<unsigned int N, class T>
using fPtr=decltype(f<N,T>)*;
template<unsigned int N, class T>
fPtr<N,T> af[N]={&f<N,T>}; // even without initialization,error still is
template<unsigned int N, class T>
void g(const decltype(af<N,T>)&){}
static_assert(std::is_same<decltype(af<1,int>),
fPtr<1,int>[1] >::value, "af is correct"); // #1
static_assert(std::is_same<decltype(g<1,int>),
void(fPtr<1,int>const(&)[1])>::value, "fun"); // #2
template<>
void g<1,int>(fPtr<1,int>const(&)[1]){}
GCC gives very misleading error message:
error: specialization of 'void g(decltype (af<N, T>)&) [with unsigned int N =
1; T = int; decltype (af<N, T>) = void (* [1])(const int*)]' after
instantiation
21 | void g<1,int>(fPtr<1,int>const(&)[1]){}
| ^
