diff options
| author | Jonathan Wakely <jwakely@redhat.com> | 2024-02-28 15:05:08 +0000 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2024-02-29 17:49:43 +0000 |
| commit | 02ca9d3f0c5d2b0255df28f021834dd67ad79bc2 (patch) | |
| tree | 9c26841d63b75dcea44bb195f2872a57b69e669b | |
| parent | f5cdda8acb06c20335855ed353ab9a441c12128a (diff) | |
libstdc++: Fix std::basic_format_arg::handle for BasicFormatters
std::basic_format_arg::handle is supposed to format its value as const
if that is valid, to reduce the number of instantiations of the
formatter's format function. I made a silly typo so that it checks
formattable_with<TD, Context> not formattable_with<const TD, Context>,
which breaks support for BasicFormatters i.e. ones that can only format
non-const types.
There's a static_assert in the handle constructor which is supposed to
improve diagnostics for trying to format a const argument with a
formatter that doesn't support it. That condition can't fail, because
the std::basic_format_arg constructor is already constrained to check
that the argument type is formattable. The static_assert can be removed.
libstdc++-v3/ChangeLog:
* include/std/format (basic_format_arg::handle::__maybe_const_t):
Fix condition to check if const type is formattable.
(basic_format_arg::handle::handle(T&)): Remove redundant
static_assert.
* testsuite/std/format/formatter/basic.cc: New test.
| -rw-r--r-- | libstdc++-v3/include/std/format | 6 | ||||
| -rw-r--r-- | libstdc++-v3/testsuite/std/format/formatter/basic.cc | 24 |
2 files changed, 25 insertions, 5 deletions
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format index 961441e355b..ee189f9086c 100644 --- a/libstdc++-v3/include/std/format +++ b/libstdc++-v3/include/std/format @@ -3210,7 +3210,7 @@ namespace __format // Format as const if possible, to reduce instantiations. template<typename _Tp> using __maybe_const_t - = __conditional_t<__formattable<_Tp>, const _Tp, _Tp>; + = __conditional_t<__formattable<const _Tp>, const _Tp, _Tp>; template<typename _Tq> static void @@ -3228,10 +3228,6 @@ namespace __format explicit handle(_Tp& __val) noexcept { - if constexpr (!__formattable<const _Tp>) - static_assert(!is_const_v<_Tp>, "std::format argument must be " - "non-const for this type"); - this->_M_ptr = __builtin_addressof(__val); auto __func = _S_format<__maybe_const_t<_Tp>>; this->_M_func = reinterpret_cast<void(*)()>(__func); diff --git a/libstdc++-v3/testsuite/std/format/formatter/basic.cc b/libstdc++-v3/testsuite/std/format/formatter/basic.cc new file mode 100644 index 00000000000..56c18864135 --- /dev/null +++ b/libstdc++-v3/testsuite/std/format/formatter/basic.cc @@ -0,0 +1,24 @@ +// { dg-do compile { target c++20 } } + +// BasicFormatter requirements do not require a const parameter. + +#include <format> + +struct X { }; + +template<> struct std::formatter<X, char> +{ + constexpr auto parse(format_parse_context& ctx) + { return ctx.begin(); } + + // Takes non-const X& + format_context::iterator format(X&, format_context& ctx) const + { + auto out = ctx.out(); + *out++ = 'x'; + return out; + } +}; + +X x; +auto s = std::format("{}", x); |