PR c++/90532 Ensure __is_constructible(T[]) is false

An array of an unknown bound is an incomplete type, so no object of such
a type can be constructed. This means __is_constructible should always
be false for an array of unknown bound.

This patch also changes the std::is_default_constructible trait to use
std::is_constructible, which now gives the right answer for arrays of
unknown bound.

gcc/cp:

	PR c++/90532 Ensure __is_constructible(T[]) is false
	* method.c (is_xible_helper): Return error_mark_node for construction
	of an array of unknown bound.

gcc/testsuite:

	PR c++/90532 Ensure __is_constructible(T[]) is false
	* g++.dg/ext/90532.C: New test.

libstdc++-v3:

	PR c++/90532 Ensure __is_constructible(T[]) is false
	* include/std/type_traits (__do_is_default_constructible_impl)
	(__is_default_constructible_atom, __is_default_constructible_safe):
	Remove.
	(is_default_constructible): Use is_constructible.
	* testsuite/20_util/is_constructible/value.cc: Check int[] case.
	* testsuite/20_util/is_default_constructible/value.cc: Likewise.
	* testsuite/20_util/is_trivially_constructible/value.cc: Likewise.
	* testsuite/20_util/is_trivially_default_constructible/value.cc:
	Likewise.

From-SVN: r271412

1 files changed, 2 insertions, 0 deletions

diff --git a/gcc/cp/method.c b/gcc/cp/method.c
index 3fb3b5a..53fa85b 100644
--- a/gcc/cp/method.c
+++ b/gcc/cp/method.c
@@ -1201,6 +1201,8 @@ is_xible_helper (enum tree_code code, tree to, tree from, bool trivial)
     expr = assignable_expr (to, from);
   else if (trivial && from && TREE_CHAIN (from))
     return error_mark_node; // only 0- and 1-argument ctors can be trivial
+  else if (TREE_CODE (to) == ARRAY_TYPE && !TYPE_DOMAIN (to))
+    return error_mark_node; // can't construct an array of unknown bound
   else
     expr = constructible_expr (to, from);
   return expr;