https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96443
Bug ID: 96443
Summary: Incorrect satisfaction value for dependent return type
placeholder constraint
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ppalka at gcc dot gnu.org
Target Milestone: ---
GCC 10.1, 10.2 and 11 fail to accept the following valid testcase.
Satisfaction checking of f's return type placeholder constraint seems to go
wrong at some point.
$ cat testcase.C
template<typename T, typename U>
concept Same = __is_same(T, U);
auto f(auto x) -> Same<decltype(x)> auto { return 0; }
int a = f(42);
$ g++ -std=c++2a testcase.C
testcase.C: In instantiation of ‘auto [requires ::Same<<placeholder>,
decltype(f::x)>] f(auto:1) [with auto:1 = int]’:
testcase.C:7:13: required from here
testcase.C:6:51: error: deduced return type does not satisfy placeholder
constraints
6 | auto f(auto x) -> Same<decltype(x)> auto { return 0; }
| ^
testcase.C:6:51: note: constraints not satisfied
testcase.C: In instantiation of ‘auto [requires ::Same<<placeholder>,
decltype(g::x)>] g(auto:2) [with auto:2 = bool]’:
testcase.C:10:15: required from here
testcase.C:9:51: error: deduced return type does not satisfy placeholder
constraints
9 | auto g(auto x) -> Same<decltype(x)> auto { return 0; } // { dg-error
"constraint" }
| ^
testcase.C:9:51: note: constraints not satisfied
testcase.C:4:9: required for the satisfaction of ‘Same<int, decltype (x)>’
testcase.C:4:16: note: ‘int’ is not the same as ‘bool’
4 | concept Same = __is_same(T, U);
| ^~~~~~~~~~~~~~~
