[C++ PATCH] Implement P0969

[Ville Voutilainen]

Tested on Linux-PPC64.

2018-04-05  Ville Voutilainen  <ville.voutilai...@gmail.com>

    gcc/cp

    Implement P0969
    * decl.c (find_decomp_class_base): Check accessibility instead
    of declared access, adjust diagnostic.

    testsuite/

    Implement P0969
    * g++.dg/cpp1z/decomp4.C: Adjust.
    * g++.dg/cpp1z/decomp38.C: New.

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 1a100c8..2cde65b 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -7322,9 +7322,9 @@ find_decomp_class_base (location_t loc, tree type, tree ret)
 	inform (DECL_SOURCE_LOCATION (field), "declared here");
 	return error_mark_node;
       }
-    else if (TREE_PRIVATE (field) || TREE_PROTECTED (field))
+    else if (!accessible_p (type, field, true))
       {
-	error_at (loc, "cannot decompose non-public member %qD of %qT",
+	error_at (loc, "cannot decompose inaccessible member %qD of %qT",
 		  field, type);
 	inform (DECL_SOURCE_LOCATION (field),
 		TREE_PRIVATE (field)
diff --git a/gcc/testsuite/g++.dg/cpp1z/decomp38.C b/gcc/testsuite/g++.dg/cpp1z/decomp38.C
new file mode 100644
index 0000000..fc69c02
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/decomp38.C
@@ -0,0 +1,48 @@
+// { dg-additional-options -std=c++17 }
+// { dg-do compile }
+
+class X
+{
+   int a, b;
+   void f()
+   {
+     auto[x,y] = *this;
+   }
+};
+
+class X2
+{
+   int a, b;
+   void f(X2& other)
+   {
+     auto[x,y] = other;
+   }
+};
+
+struct X3
+{
+  friend void foo();
+private:
+  int a;
+};
+
+void foo()
+{
+  X3 x;
+  auto [a] = x;
+}
+
+struct X4
+{
+  int a;
+};
+
+struct X5 : private X4
+{
+  friend void foo2();
+};
+
+void foo2() {
+  X5 x;
+  auto [a] = x;
+}
diff --git a/gcc/testsuite/g++.dg/cpp1z/decomp4.C b/gcc/testsuite/g++.dg/cpp1z/decomp4.C
index e50b882..69b5455 100644
--- a/gcc/testsuite/g++.dg/cpp1z/decomp4.C
+++ b/gcc/testsuite/g++.dg/cpp1z/decomp4.C
@@ -18,10 +18,10 @@ test (A &a, B &b, C &c, D &d, E &e, F &f, G &g, H &h, I &i)
 					// { dg-warning "structured bindings only available with -std=c..17 or -std=gnu..17" "" { target c++14_down } .-1 }
   auto [ k ] { b };			// { dg-error "cannot decompose class type 'B' because it has an anonymous union member" }
 					// { dg-warning "structured bindings only available with -std=c..17 or -std=gnu..17" "" { target c++14_down } .-1 }
-  auto [ l, l2 ] = c;			// { dg-error "cannot decompose non-public member 'C::b' of 'C'" }
+  auto [ l, l2 ] = c;			// { dg-error "cannot decompose inaccessible member 'C::b' of 'C'" }
 					// { dg-warning "structured bindings only available with -std=c..17 or -std=gnu..17" "" { target c++14_down } .-1 }
   auto [ m ] = d;			// { dg-warning "structured bindings only available with -std=c..17 or -std=gnu..17" "" { target c++14_down } }
-  auto [ n ] { e };			// { dg-error "cannot decompose non-public member 'E::a' of 'E'" }
+  auto [ n ] { e };			// { dg-error "cannot decompose inaccessible member 'E::a' of 'E'" }
 					// { dg-warning "structured bindings only available with -std=c..17 or -std=gnu..17" "" { target c++14_down } .-1 }
   auto [ o ] { f };			// { dg-warning "structured bindings only available with -std=c..17 or -std=gnu..17" "" { target c++14_down } }
   auto & [ p ] { g };			// { dg-error "cannot decompose class type 'G': both it and its base class 'F' have non-static data members" }