c++: Fix __is_*constructible/assignable for templates [PR102305]

is_xible_helper returns error_mark_node (i.e. false from the traits)
for abstract classes by testing ABSTRACT_CLASS_TYPE_P (to) early.
Unfortunately, as the testcase shows, that doesn't work on class templates
that haven't been instantiated yet, ABSTRACT_CLASS_TYPE_P for them is false
until it is instantiated, which is done when the routine later constructs
a dummy object with that type.

The following patch fixes this by calling complete_type first, so that
ABSTRACT_CLASS_TYPE_P test will work properly, while keeping the handling
of arrays with unknown bounds, or incomplete types where it is done
currently.

2021-09-14  Jakub Jelinek  <jakub@redhat.com>

	PR c++/102305
	* method.c (is_xible_helper): Call complete_type on to.

	* g++.dg/cpp0x/pr102305.C: New test.

diff --git a/gcc/cp/method.c b/gcc/cp/method.c
index 353046d3e470996261afa8b819a67b8ed8068ec1..32f7186a7749931b48f38f471a758329a86bc0b5 100644 (file)
--- a/gcc/cp/method.c
+++ b/gcc/cp/method.c
@@ -2081,6 +2081,7 @@ constructible_expr (tree to, tree from)
 static tree
 is_xible_helper (enum tree_code code, tree to, tree from, bool trivial)
 {
+  to = complete_type (to);
   deferring_access_check_sentinel acs (dk_no_deferred);
   if (VOID_TYPE_P (to) || ABSTRACT_CLASS_TYPE_P (to)
       || (from && FUNC_OR_METHOD_TYPE_P (from)

diff --git a/gcc/testsuite/g++.dg/cpp0x/pr102305.C b/gcc/testsuite/g++.dg/cpp0x/pr102305.C
new file mode 100644 (file)
index 0000000..e63adcf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/pr102305.C
@@ -0,0 +1,39 @@
+// PR c++/102305
+// { dg-do compile { target c++11 } }
+
+namespace std
+{
+  template<typename _Tp, _Tp __v>
+    struct integral_constant
+    {
+      static constexpr _Tp value = __v;
+      typedef integral_constant<_Tp, __v> type;
+    };
+
+  template<typename _Tp, _Tp __v>
+    constexpr _Tp integral_constant<_Tp, __v>::value;
+
+  typedef integral_constant<bool, true> true_type;
+  typedef integral_constant<bool, false> false_type;
+
+  template<bool __v>
+    using bool_constant = integral_constant<bool, __v>;
+
+  template<typename _Tp, typename... _Args>
+    struct is_constructible
+    : public bool_constant<__is_constructible(_Tp, _Args...)>
+    {
+    };
+}
+
+template<typename>
+struct A {
+  virtual ~A() = 0;
+};
+
+struct B {
+  virtual ~B() = 0;
+};
+
+static_assert(!std::is_constructible<A<int> >::value, "");
+static_assert(!std::is_constructible<B>::value, "");