https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85155
Bug ID: 85155
Summary: Suboptimal error messages when using noexcept(false)
on defaulted dtor
Product: gcc
Version: 8.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vz-gcc at zeitlins dot org
Target Milestone: ---
Consider the following test program:
% cat -n dtor_def_noexcept.cpp
1 struct B {
2 virtual ~B() noexcept(false) = default;
3 };
4
5 struct D : B {
6 virtual ~D() { throw 17; }
7 };
8
9 int main()
10 {
11 try {
12 D d;
13 return 1;
14 } catch (int n) {
15 return n;
16 }
17
18 return 0;
19 }
Compiling it with g++ 8 (gcc version 8.0.1 20180321 (experimental) [trunk
revision 258712] (Debian 8-20180321-1)) results in the following not really
obvious to interpret errors:
% g++-8 -std=c++17 -Wall dtor_def_noexcept.cpp
dtor_def_noexcept.cpp:6:13: error: non-deleted function ‘virtual D::~D()’
virtual ~D() { throw 17; }
^
dtor_def_noexcept.cpp:2:13: error: overriding deleted function ‘virtual
B::~B()’
virtual ~B() noexcept(false) = default;
^
dtor_def_noexcept.cpp: In destructor ‘virtual D::~D()’:
dtor_def_noexcept.cpp:6:18: error: use of deleted function ‘B::~B()’
virtual ~D() { throw 17; }
^
dtor_def_noexcept.cpp:2:13: note: ‘virtual B::~B() noexcept (false)’ is
implicitly deleted because its exception-specification does not match the
implicit exception-specification ‘noexcept’
virtual ~B() noexcept(false) = default;
^
dtor_def_noexcept.cpp:6:26: warning: throw will always call terminate()
[-Wterminate]
virtual ~D() { throw 17; }
^~
dtor_def_noexcept.cpp:6:26: note: in C++11 destructors default to noexcept
dtor_def_noexcept.cpp: In function ‘int main()’:
dtor_def_noexcept.cpp:12:11: error: use of deleted function ‘D::D()’
D d;
^
dtor_def_noexcept.cpp:5:8: note: ‘D::D()’ is implicitly deleted because the
default definition would be ill-formed:
struct D : B {
^
dtor_def_noexcept.cpp:5:8: error: use of deleted function ‘virtual B::~B()’
All of this is correct, of course, but compare it with the error message given
by clang:
% clang-7 -std=c++17 -Wall dtor_def_noexcept.cpp
dtor_def_noexcept.cpp:2:13: error: exception specification of explicitly
defaulted destructor does not match the calculated one
virtual ~B() noexcept(false) = default;
^
1 error generated.
which seems much more clear. It would be nice if gcc error messages could be
improved to emphasize the important one, i.e. that noexcept(false) doesn't
match "= default".
