re PR c++/83958 (ICE: Segmentation fault (in find_decomp_class_base))

	PR c++/83958
	* decl.c (cp_finish_decomp): Diagnose if reference structure binding
	refers to incomplete type.

	* g++.dg/cpp1z/decomp35.C: New test.

From-SVN: r256984

gcc/cp/ChangeLog

+2018-01-23  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/83958
+	* decl.c (cp_finish_decomp): Diagnose if reference structure binding
+	refers to incomplete type.
+
 2018-01-23  Nathan Sidwell  <nathan@acm.org>
 
 	Deprecate ARM-era for scope handling

gcc/cp/decl.c

@@ -7435,6 +7435,12 @@ cp_finish_decomp (tree decl, tree first, unsigned int count)
       type = complete_type (TREE_TYPE (type));
       if (type == error_mark_node)
 	goto error_out;
+      if (!COMPLETE_TYPE_P (type))
+	{
+	  error_at (loc, "structured binding refers to incomplete type %qT",
+		    type);
+	  goto error_out;
+	}
     }
 
   tree eltype = NULL_TREE;

gcc/testsuite/ChangeLog

+2018-01-23  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/83958
+	* g++.dg/cpp1z/decomp35.C: New test.
+
 2018-01-23  Nathan Sidwell  <nathan@acm.org>
 
 	* g++.dg/cpp0x/range-for10.C: Adjust.

gcc/testsuite/g++.dg/cpp1z/decomp35.C

+// PR c++/83958
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+template <typename = void> struct A;
+class B;
+template <typename, typename, typename = A<>> class C;
+template <typename, typename> struct D;
+template <typename T, typename U, typename V, typename, typename, typename W>
+struct E {
+  using X = W;
+  X operator* ();
+  T operator++ ();
+  template <typename P, typename R, typename S, typename Q>
+  bool operator!= (E<P, U, V, R, S, Q>);
+};
+template <typename T, typename U, typename>
+struct F {
+  class G;
+  using H = D<T, U>;
+  using I = E<G, T, U, G, H, H &>;
+  class G : public I {};
+  G begin ();
+  G end ();
+};
+template <typename T, typename U, typename V> struct C : F<T, U, V> {
+  using J = F<T, U, V>;
+  using J::begin;
+  using J::end;
+};
+using K = class L;
+struct M {
+  void foo () { for (auto & [ a ] : m) {} }	// { dg-error "incomplete type" }
+  C<K, B> m;					// { dg-warning "only available with" "" { target c++14_down } .-1 }
+};