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Trying to improve errors in the unformattable case (#3478)

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Barry Revzin 2023-07-01 08:46:04 -05:00 committed by GitHub
parent e4c8cfe38e
commit de4705f84d
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1 changed files with 20 additions and 0 deletions
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20
include/fmt/core.h
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@ -1548,6 +1548,11 @@ constexpr auto encode_types() -> unsigned long long {
(encode_types<Context, Args...>() << packed_arg_bits);
}
#if defined(__cpp_if_constexpr)
// This type is intentionally undefined, only used for errors
template <typename T, typename Char> struct type_is_unformattable_for;
#endif
template <bool PACKED, typename Context, typename T, FMT_ENABLE_IF(PACKED)>
FMT_CONSTEXPR FMT_INLINE auto make_arg(T& val) -> value<Context> {
using arg_type = remove_cvref_t<decltype(arg_mapper<Context>().map(val))>;
@ -1565,6 +1570,11 @@ FMT_CONSTEXPR FMT_INLINE auto make_arg(T& val) -> value<Context> {
"Formatting of non-void pointers is disallowed.");
constexpr bool formattable = !std::is_same<arg_type, unformattable>::value;
#if defined(__cpp_if_constexpr)
if constexpr (!formattable) {
type_is_unformattable_for<T, typename Context::char_type> _;
}
#endif
static_assert(
formattable,
"Cannot format an argument. To make type T formattable provide a "
@ -2529,7 +2539,17 @@ FMT_CONSTEXPR auto parse_format_specs(ParseContext& ctx)
mapped_type_constant<T, context>::value != type::custom_type,
decltype(arg_mapper<context>().map(std::declval<const T&>())),
typename strip_named_arg<T>::type>;
#if defined(__cpp_if_constexpr)
if constexpr (std::is_default_constructible_v<
formatter<mapped_type, char_type>>) {
return formatter<mapped_type, char_type>().parse(ctx);
} else {
type_is_unformattable_for<T, char_type> _;
return ctx.begin();
}
#else
return formatter<mapped_type, char_type>().parse(ctx);
#endif
}
// Checks char specs and returns true iff the presentation type is char-like.