https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111723
Bug ID: 111723 Summary: #pragma GCC system_header suppresses errors from narrowing conversions Product: gcc Version: 13.2.1 Status: UNCONFIRMED Keywords: accepts-invalid Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: de34 at live dot cn Target Milestone: --- In the following program, the conversions are narrowing, but only the one for nonstd::in_fun_result is rejected. When -Wsystem-headers is used, then the narrowing conversion for std::ranges::in_fun_result are correctly diagnosed. But if -pedantic-errors and -Wsystem-headers are used together, some standard headers are rejected. Godbolt link: https://godbolt.org/z/fT7b16eoe ``` #include <algorithm> #include <concepts> #include <utility> namespace nonstd { template<class I, class F> struct in_fun_result { [[no_unique_address]] I in; [[no_unique_address]] F fun; template<class I2, class F2> requires std::convertible_to<const I&, I2> && std::convertible_to<const F&, F2> constexpr operator in_fun_result<I2, F2>() const& { return {in, fun}; } template<class I2, class F2> requires std::convertible_to<I, I2> && std::convertible_to<F, F2> constexpr operator in_fun_result<I2, F2>() && { return {std::move(in), std::move(fun)}; } }; } int main() { std::ranges::in_fun_result<int, int> r1{}; std::ranges::in_fun_result<short, short> r2 = r1; // should be error, but not diagnosed by default nonstd::in_fun_result<int, int> r3{}; nonstd::in_fun_result<short, short> r4 = r3; // error, rejected with -pedantic-errors } ``` It seems to me that #pragma GCC system_header shouldn't suppress errors from narrowing conversions, because the diagnostics are required by the standard.