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Avoid LNK2001 in c++20 when /GL (Whole program optimization) is ON with MSVC #5939

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Merged
rwgk merged 1 commit into from
Dec 23, 2025
+10 −2
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Avoid LNK2001 in c++20 when /GL (Whole program optimization) is ON with MSVC #5939

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12 changes: 10 additions & 2 deletions include/pybind11/pybind11.h
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,12 @@ PYBIND11_WARNING_DISABLE_CLANG("-Wgnu-zero-variadic-macro-arguments")
# include <cxxabi.h>
#endif

#if defined(__cpp_if_constexpr) && __cpp_if_constexpr >= 201606
# define PYBIND11_MAYBE_CONSTEXPR constexpr
#else
# define PYBIND11_MAYBE_CONSTEXPR
#endif

PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)

/* https://stackoverflow.com/questions/46798456/handling-gccs-noexcept-type-warning
Expand Down Expand Up @@ -3606,13 +3612,15 @@ function get_override(const T *this_ptr, const char *name) {
auto o = override(__VA_ARGS__); \
PYBIND11_WARNING_PUSH \
PYBIND11_WARNING_DISABLE_MSVC(4127) \
if (pybind11::detail::cast_is_temporary_value_reference<ret_type>::value \
if PYBIND11_MAYBE_CONSTEXPR ( \
pybind11::detail::cast_is_temporary_value_reference<ret_type>::value \
&& !pybind11::detail::is_same_ignoring_cvref<ret_type, PyObject *>::value) { \
static pybind11::detail::override_caster_t<ret_type> caster; \
return pybind11::detail::cast_ref<ret_type>(std::move(o), caster); \
} else { \
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@rwgk rwgk Dec 21, 2025

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Do we need the else here? The other if branch ends with a return, the else seems redundant.

I think it'd be slightly better to leave the code down here as-is, in part because the PYBIND11_WARNING_POP is then before the return below.

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@hellokenlee hellokenlee Dec 23, 2025 •
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The else is added here because the CI checks complained “warning C4702: unreachable code”( in which case the constexpr if evals true, and the code outside that constexpr if becomes unreachable ). Since the CI checks turn on "warning as error", the CI checks will failed.

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@hellokenlee hellokenlee Dec 23, 2025

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Sorry for the late reply.

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@rwgk rwgk Dec 23, 2025

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Thanks for the explanation!

The warning will be annoying, seems like a second C4127, not keeping up with the times (templates), so I think we'll probably wind up suppressing C4702 as we make more use of constexpr in the future ... but your solution is good for now.

return pybind11::detail::cast_safe<ret_type>(std::move(o)); \
} \
PYBIND11_WARNING_POP \
return pybind11::detail::cast_safe<ret_type>(std::move(o)); \
} \
} while (false)

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