https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89442
Bug ID: 89442
Summary: [concepts] missing "wrong number of template
arguments" error in requires-clause
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
template<typename T, typename U> constexpr bool foo = true;
template<typename T> int f(T) requires foo<T> { return 0; }
int i = f(0);
$ g++17 -fconcepts con.cc -c
con.cc:5:12: error: cannot call function 'int f(T) requires foo<T> [with T =
int]'
5 | int i = f(0);
| ^
con.cc:3:26: note: constraints not satisfied
3 | template<typename T> int f(T) requires foo<T> { return 0; }
| ^
con.cc:3:26: note: 'foo<T>' evaluated to false
The error tells me that foo<T> evaluated to false, but it should say foo<T> is
invalid and report an ill-formed constraint, as in this equivalent version:
template<typename, typename>
struct bar { static constexpr bool value = true; };
template<typename T> int f(T) requires bar<T>::value { return 0; }
int i = f(0);
This second one (correctly) says:
con.cc:4:45: error: wrong number of template arguments (1, should be 2)
4 | template<typename T> int f(T) requires bar<T>::value { return 0; }
| ^
con.cc:2:8: note: provided for 'template<class, class> struct bar'
2 | struct bar { static constexpr bool value = true; };
| ^~~
con.cc:6:12: error: cannot call function 'int f(T) requires
<erroneous-expression> [with T = int]'
6 | int i = f(0);
| ^
con.cc:4:26: note: constraints not satisfied
4 | template<typename T> int f(T) requires bar<T>::value { return 0; }
| ^
con.cc:6:12: note: ill-formed constraint
6 | int i = f(0);
| ^
