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From: "vincent-gcc at vinc17 dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/105499] inconsistency between -Werror=c++-compat and g++ in
 __extension__ block
Date: Mon, 31 Oct 2022 14:17:56 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105499

--- Comment #6 from Vincent Lef=C3=A8vre <vincent-gcc at vinc17 dot net> ---
To be clear... I'm not sure about what kind of compatibility warnings one c=
an
get, but it is OK to silence valid extensions, i.e. those that will not giv=
e an
error. But invalid extensions, i.e. those that would give an error with a
compat-implied compiler (like in the testcase), should not be silenced by
__extension__.

The problem is that in my original testcase, __extension__ was used in orde=
r to
silence the warning for the ({...}) construct, which is still valid with g+=
+.
But as a side effect, it also silences the conversion from the "int *p =3D =
q;",
which is invalid in C++ (and is actually *not* an extension as it fails as
shown in my bug report).=