https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98249
Bug ID: 98249
Summary: Improper ADL on the `arg` in `new (arg) T`
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: arthur.j.odwyer at gmail dot com
Target Milestone: ---
// https://godbolt.org/z/xavfej
#include <new>
struct Incomplete;
template<class T> struct Holder { T t; };
Holder<Incomplete> *p;
void test() {
::new (p) int;
new (p) int;
}
In an "ADL call," the compiler needs to compute the associated types of
`Holder<Incomplete>`, which means it needs to complete that type in order to
check for friend declarations. In a "non-ADL call" (such as a qualified call),
the compiler does NOT need to complete `Holder<Incomplete>`. Since completing
`Holder<Incomplete>` produces a hard error, we can detect the difference
between an ADL and a non-ADL call.
All other compilers use "non-ADL calls" for both `::new (p) int` and `new (p)
int`: they don't attempt to complete the incomplete type. GCC uses "ADL calls"
for both, which means it hard-errors on both lines.
I'm not sure what the Standard has to say about this, but GCC disagrees with
all of Clang/MSVC/ICC, so I think GCC ought to change.
(Detected while testing libc++ patch https://reviews.llvm.org/D92884)
