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Add -Wmaybe-uninitialized pragma to union storage constructors

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GCC 7+ produces false-positive -Wmaybe-uninitialized warnings at -O3
when deeply inlining through union constructors that initialize one
member while another (dummy_) exists. This is the same class of false
positive addressed in boostorg/variant2#55.

The pragmas are placed around the forwarding constructors in both
constexpr_union_storage_t and fallback_union_storage_t.
This commit is contained in:
Alan de Freitas
2026-02-23 22:56:04 -05:00
parent fa52755c88
commit 88e2378c8a
1 changed files with 22 additions and 0 deletions
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include/boost/optional/detail/union_optional.hpp
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@@ -74,9 +74,20 @@ union constexpr_union_storage_t
constexpr constexpr_union_storage_t( trivial_init_t ) noexcept : dummy_() {};
#if defined(BOOST_GCC) && (__GNUC__ >= 7)
// false positive, see https://github.com/boostorg/variant2/issues/55,
// https://github.com/boostorg/url/issues/979
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
#endif
template <class... Args>
constexpr constexpr_union_storage_t( Args&&... args ) : value_(forward_<Args>(args)...) {}
#if defined(BOOST_GCC) && (__GNUC__ >= 7)
# pragma GCC diagnostic pop
#endif
//~constexpr_union_storage_t() = default; // No need to destroy a trivially-destructible type
};
@@ -88,9 +99,20 @@ union fallback_union_storage_t
constexpr fallback_union_storage_t( trivial_init_t ) noexcept : dummy_() {};
#if defined(BOOST_GCC) && (__GNUC__ >= 7)
// false positive, see https://github.com/boostorg/variant2/issues/55,
// https://github.com/boostorg/url/issues/979
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
#endif
template <class... Args>
constexpr fallback_union_storage_t( Args&&... args ) : value_(forward_<Args>(args)...) {}
#if defined(BOOST_GCC) && (__GNUC__ >= 7)
# pragma GCC diagnostic pop
#endif
~fallback_union_storage_t(){} // My owner will destroy the `T` if needed.
// Cannot default in a union with nontrivial `T`.
};