Hi!
In C++20, types with user-declared constructors are not aggregate types,
while in C++17 only types with user-provided or explicit constructors.
In check_bases_and_members we handle it properly:
CLASSTYPE_NON_AGGREGATE (t)
|= ((cxx_dialect < cxx2a
? type_has_user_provided_or_explicit_constructor (t)
: TYPE_HAS_USER_CONSTRUCTOR (t))
|| TYPE_POLYMORPHIC_P (t));
but for templates the code right now behaves the C++20 way regardless of the
selected standard.
The following patch tweaks finish_struct to match check_bases_and_members.
I had to add !CLASSTYPE_NON_AGGREGATE check because
type_has_user_provided_or_explicit_constructor -> user_provided_p ICEd
on inherited ctors represented as USING_DECLs.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2019-12-10 Jakub Jelinek <ja...@redhat.com>
PR c++/92869
* class.c (finish_struct): For C++17 and earlier, check
type_has_user_provided_or_explicit_constructor rather than
TYPE_HAS_USER_CONSTRUCTOR whether to set CLASSTYPE_NON_AGGREGATE.
* g++.dg/cpp0x/aggr3.C: New test.
--- gcc/cp/class.c.jj 2019-12-06 00:40:44.525629037 +0100
+++ gcc/cp/class.c 2019-12-10 14:18:41.171380767 +0100
@@ -7456,7 +7456,13 @@ finish_struct (tree t, tree attributes)
/* Remember current #pragma pack value. */
TYPE_PRECISION (t) = maximum_field_alignment;
- if (TYPE_HAS_USER_CONSTRUCTOR (t))
+ if (cxx_dialect < cxx2a)
+ {
+ if (!CLASSTYPE_NON_AGGREGATE (t)
+ && type_has_user_provided_or_explicit_constructor (t))
+ CLASSTYPE_NON_AGGREGATE (t) = 1;
+ }
+ else if (TYPE_HAS_USER_CONSTRUCTOR (t))
CLASSTYPE_NON_AGGREGATE (t) = 1;
/* Fix up any variants we've already built. */
--- gcc/testsuite/g++.dg/cpp0x/aggr3.C.jj 2019-12-10 14:25:22.344231923
+0100
+++ gcc/testsuite/g++.dg/cpp0x/aggr3.C 2019-12-10 14:23:31.700927787 +0100
@@ -0,0 +1,20 @@
+// PR c++/92869
+// { dg-do compile { target c++11 } }
+
+struct A {
+ A () = default;
+ A (const A &) = default;
+ A (A &&) = default;
+ int arr[3];
+};
+
+template <typename T, int N>
+struct B {
+ B () = default;
+ B (const B &) = default;
+ B (B &&) = default;
+ T arr[N];
+};
+
+A a = { { 1, 2, 3 } }; // { dg-error "could not convert" "" { target
c++2a } }
+B<int, 3> b = { { 1, 2, 3 } }; // { dg-error "could not convert" "" { target
c++2a } }
Jakub
