https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107545
Bug ID: 107545
Summary: __is_abstract intrinsic fails to compile on incomplete
unions
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: eric41293 at comcast dot net
Target Milestone: ---
[meta.unary.props] states for std::is_abstract, "If T is a non-union class
type, T shall be a complete type." A union cannot have virtual functions, so an
incomplete union can safely be determined not to be abstract. Thus, is_abstract
is required to work for incomplete unions. However, the __is_abstract
intrinsic, and hence also std::is_abstract, generates a compiler error in this
case:
$ g++ --version
g++ (Ubuntu 12.1.0-2ubuntu1~22.04) 12.1.0
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ cat > is_abstract.cpp
union U;
bool b = __is_abstract(U);
$ g++ is_abstract.cpp
is_abstract.cpp:2:25: error: invalid use of incomplete type ‘union U’
2 | bool b = __is_abstract(U);
| ^
is_abstract.cpp:1:7: note: forward declaration of ‘union U’
1 | union U;
| ^
