https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115715
Bug ID: 115715
Summary: gcc seems to incorrectly accept illegal constexpr
constructor in virtual inheritance and static template
class member
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Keywords: accepts-invalid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: rush102333 at gmail dot com
Target Milestone: ---
We have encountered unexpected compiler output by compiling the following code
with gcc-13.2:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
struct Storage {
constexpr Storage(int) {}
};
struct Derived :virtual Storage {
using Storage::Storage;
};
template<typename>
struct Template {
static constexpr Derived kDerived{0};
};
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The compiler normally accepts the code without providing any error message. But
to our knowledge, constructors of classes having virtual bases are not allowed
to be declared as constexpr, even if the constructor of the base class is
declared constexpr.
https://godbolt.org/z/exjb3v9MW
Additionally, changing the class "Template" to a non-template class makes GCC
correctly reject the code by reporting the following error:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<source>:11:40: error: 'constexpr Derived::Derived(int) [inherited from
Storage]' called in a constant expression
11 | static constexpr Derived kDerived{0};
| ^
<source>:6:20: note: 'constexpr Derived::Derived(int) [inherited from Storage]'
is not usable as a 'constexpr' function because:
6 | using Storage::Storage;
| ^~~~~~~
<source>:6:20: error: 'struct Derived' has virtual base classes
Compiler returned: 1
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
https://godbolt.org/z/Gx5Gjxzn4
Clang always rejects the code no matter whether "Template" is actually a
template class or not by giving error messages similar to that provided by GCC
above.
We think that should probably be a bug of GCC and need to be taken a look at.
