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From: "jason at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/101500] [C++17] [DR2311] gcc accepts the code with extra
 curly braces
Date: Fri, 15 Apr 2022 15:44:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101500

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[9/10/11/12 Regression] gcc |[C++17] [DR2311] gcc
                   |accepts the code with extra |accepts the code with extra
                   |curly braces                |curly braces
             Status|NEW                         |SUSPENDED
                URL|                            |wg21.link/cwg2311

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
This seems like an instance of issue 2311: with C++17 mandatory copy elisio=
n,
do we really want an actual call to the move constructor in this case?  The
testcase is rejected in C++14 mode, as expected.

The standard says that we try to call a constructor, initializing the argum=
ent
with {A{}}.  So we in turn look for an A constructor to initialize the
argument, initializing its argument from A{}.  Under 2311, does this result=
 in
still an rvalue?  And the enclosing constructor call, still the same rvalue?

This seems parallel to

const A a =3D A(A(A()));

which is also accepted by clang in C++17 mode.

Perhaps we want to raise the priority of issue 2311.=