<format>: Conditionally emit special diagnostic message for lack of const
#4461
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Also emit `static_assert` error messages for `basic_format_arg::handle`.
frederick-vs-ja
commented
Mar 11, 2024
| using _Td = remove_const_t<_Ty>; | ||
| // doesn't drop const-qualifier per an unnumbered LWG issue | ||
| using _Tq = conditional_t<_Formattable_with<const _Ty, _Context>, const _Ty, _Ty>; | ||
| if constexpr (_Formattable_with_non_const<_Tq, _Context>) { |
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This ctor is exposition-only per [format.arg]/10 but is public in MSVC STL...
Perhaps we should consider making it private (in another PR, together with non-Standard public ctors of basic_format_context).
StephanTLavavej
approved these changes
Mar 13, 2024
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|
I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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static_assert(true, "Thanks! 🎉😸☑️"); |
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Fixes #4202.
Also adds
static_assertmessages in the constructor body ofbasic_format_arg::handle, and moves thestatic_asserts into the lambda body.Currently, Clang emits 2
static_assertfailures for such an error, one inmake_(w)format_args, one in thehandlector. Because lack offormatterspecialization orconstonformatcan triggerstatic_assertfailure in the constructor body ofbasic_format_arg::handlenow.This PR slightly worsens the error messages for Clang (2 similar
static_assertmessages will be emitted). However, it seems that cleaner error messages can be achieved by conditional compilation (skippingstatic_asserts inmake_(w)format_argsfor Clang).