https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81349
Bug ID: 81349
Summary: Classes with deleted constructor templates incorrectly
labeled as non-aggregates
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: eraz at umich dot edu
Target Milestone: ---
Simple test case (https://wandbox.org/permlink/HrAlAYZCEoJJMo1w):
#include <type_traits>
struct S {
template <typename T>
S(T) = delete;
}
int main() {
static_assert(std::is_aggregate_v<T>);
}
According to [dcl.init.aggr-1] (http://eel.is/c++draft/dcl.init.aggr#1), the
class `S` satisifes the requirements of an aggregate. The constructor template
is not user-provided since it is explicitly deleted on its first declaration
(http://eel.is/c++draft/dcl.fct.def.default#5.sentence-2). The rest of the
requirements are evidently satisfied.
Consequently, this bug manifests as an invalid selection of the constructor
template as an overload candidate when attempting aggregate initialization
(https://wandbox.org/permlink/jDwulQNsoAR5BIIT). This behavior can be observed
with every GCC version back to 4.7.3 compiled using the C++11 standard
(https://wandbox.org/permlink/5EvKUdxllToCDbYH). Though the requirements have
changed in C++17 from that in C++11 and C++14
(https://timsong-cpp.github.io/cppwp/n3337/dcl.init.aggr#1), the class still
satisfies the requirements but is treated as a non-aggregate type.
