https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119517
Bug ID: 119517
Summary: formatter for chrono types are underconstrained
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: tkaminsk at gcc dot gnu.org
Target Milestone: ---
The parse and format methods on the formatters for chrono types,
currently accept unconstrained types as template parameter.
This in combination with lack of requirements on CharT,
leads to situation when formattable<Chrono, Any> is satisfied
for std::chrono type Chrono and any type Any.
As illustration following static assert passes:
static_assert(std::formattable<std::chrono::weekday, int>);
static_assert(std::formattable<std::chrono::sys_days, int>);
static_assert(std::formattable<std::chrono::weekday, char16_t>);
static_assert(std::formattable<std::chrono::sys_days, char16_t>);
// https://godbolt.org/z/oYsY3EqrY
The standard does not specify signatures for these functions,
instead of specifies that enabled specialization for such types
are provided. This implies that parse method needs to be valid
basic_format_parse_context<CharT> and format need to acccept
basic_format_context<Out, CharT> for any Out.
