From: Jonathan Wakely <jwakely@redhat.com>
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: [committed] libstdc++: Improve diagnostics for invalid std::format calls
Date: Fri, 14 Apr 2023 12:00:22 +0100 [thread overview]
Message-ID: <20230414110022.359953-1-jwakely@redhat.com> (raw)
Tested powerpc64le-linux. Pushed to trunk.
-- >8 --
Add a static_assert and a comment so that calling std::format for
unformattable argument types will now show:
/home/jwakely/gcc/13/include/c++/13.0.1/format:3563:22: error: static assertion failed: std::formatter must be specialized for each format arg
3563 | static_assert((is_default_constructible_v<formatter<_Args, _CharT>> && ...),
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
and:
140 | formatter() = delete; // No std::formatter specialization for this type.
libstdc++-v3/ChangeLog:
* include/std/format (formatter): Add comment to deleted default
constructor of primary template.
(_Checking_scanner): Add static_assert.
---
libstdc++-v3/include/std/format | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 72b6b450ad1..e4ef4f9b6d9 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -137,7 +137,7 @@ namespace __format
template<typename _Tp, typename _CharT = char>
struct formatter
{
- formatter() = delete;
+ formatter() = delete; // No std::formatter specialization for this type.
formatter(const formatter&) = delete;
formatter& operator=(const formatter&) = delete;
};
@@ -3560,6 +3560,10 @@ namespace __format
template<typename _CharT, typename... _Args>
class _Checking_scanner : public _Scanner<_CharT>
{
+ static_assert(
+ (is_default_constructible_v<formatter<_Args, _CharT>> && ...),
+ "std::formatter must be specialized for each type being formatted");
+
public:
constexpr
_Checking_scanner(basic_string_view<_CharT> __str)
@@ -3581,17 +3585,17 @@ namespace __format
__builtin_unreachable();
}
- template<typename _Head, typename... _Tail>
+ template<typename _Tp, typename... _OtherArgs>
constexpr void
_M_parse_format_spec(size_t __id)
{
if (__id == 0)
{
- formatter<_Head, _CharT> __f;
+ formatter<_Tp, _CharT> __f;
this->_M_pc.advance_to(__f.parse(this->_M_pc));
}
- else if constexpr (sizeof...(_Tail) != 0)
- _M_parse_format_spec<_Tail...>(__id - 1);
+ else if constexpr (sizeof...(_OtherArgs) != 0)
+ _M_parse_format_spec<_OtherArgs...>(__id - 1);
else
__builtin_unreachable();
}
--
2.39.2
reply other threads:[~2023-04-14 11:00 UTC|newest]
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