libstdc++: Prevent dangling references in std::unique_ptr::operator*

LWG 4148 (approved in Wrocław, November 2024) makes it ill-formed to
dereference a std::unique_ptr if that would return a dangling reference.

That can happen with a custom pointer type and a const-qualified
element_type, such that std::add_lvalue_reference_t<element_type> is a
reference-to-const that could bind to a short-lived temporary.

In C++26 the compiler diagnoses this as an error anyway:
bits/unique_ptr.h:457:16: error: returning reference to temporary [-Wreturn-local-addr]
But that can be disabled with -Wno-return-local-addr so the
static_assert ensures it is enforced consistently.

libstdc++-v3/ChangeLog:

	* include/bits/unique_ptr.h (unique_ptr::operator*): Add
	static_assert to check for dangling reference, as per LWG 4148.
	* testsuite/20_util/unique_ptr/lwg4148.cc: New test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

0 files changed, 0 insertions, 0 deletions