https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115676
Bug ID: 115676
Summary: gcc allows invalid calling to implicitly-deleted
default constructor of a template derived class in
template function
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: ---
The following invalid code is accepted by gcc-13.2.0 and gcc-trunk:
~~~~~~~~~~~~~~~~~~~~~~
struct empty{
};
template <int size>
struct A
: public empty
{
const int is_valid;
};
template <class T>
void check_a()
{
const A<0> a {};
}
~~~~~~~~~~~~~~~~~~~~~~
It can be seen that the template class "A" is non-trivial because it has an
empty base class. Thus, the default constructor of "A" should be implicitly
deleted, and the initialization statement "const A<0> a{}" should be invalid.
But when the initialization happens in a template function, GCC seems to ignore
the error. Changing "check_a" to a non-template function can make the compiler
reject the code by giving the following error message:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<source>: In function 'void check_a()':
<source>:14:17: error: use of deleted function 'A<0>::A()'
14 | const A<0> a {};
| ^
<source>:5:8: note: 'A<0>::A()' is implicitly deleted because the default
definition would be ill-formed:
5 | struct A
| ^
<source>: At global scope:
<source>:5:8: error: uninitialized const member in 'struct A<0>'
<source>:8:15: note: 'const int A<0>::is_valid' should be initialized
8 | const int is_valid;
| ^~~~~~~~
<source>: In function 'void check_a()':
<source>:14:17: note: use '-fdiagnostics-all-candidates' to display considered
candidates
14 | const A<0> a {};
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Please check https://godbolt.org/z/nGxPdn9jf
