PR c++/52321 print note for static_cast to/from incomplete type

	PR c++/52321
	* typeck.c (build_static_cast): Print a note when the destination
	type or the operand is a pointer/reference to incomplete class type.

From-SVN: r267219

gcc/cp/ChangeLog

+2018-12-17  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR c++/52321
+	* typeck.c (build_static_cast): Print a note when the destination
+	type or the operand is a pointer/reference to incomplete class type.
+
 2018-12-16  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/88482

gcc/cp/typeck.c

@@ -7348,8 +7348,21 @@ build_static_cast (tree type, tree oexpr, tsubst_flags_t complain)
     }
 
   if (complain & tf_error)
+    {
       error ("invalid static_cast from type %qT to type %qT",
 	     TREE_TYPE (expr), type);
+      if ((TYPE_PTR_P (type) || TYPE_REF_P (type))
+	  && CLASS_TYPE_P (TREE_TYPE (type))
+	    && !COMPLETE_TYPE_P (TREE_TYPE (type)))
+	inform (DECL_SOURCE_LOCATION (TYPE_MAIN_DECL (TREE_TYPE (type))),
+		"class type %qT is incomplete", TREE_TYPE (type));
+      tree expr_type = TREE_TYPE (expr);
+      if (TYPE_PTR_P (expr_type))
+	expr_type = TREE_TYPE (expr_type);
+      if (CLASS_TYPE_P (expr_type) && !COMPLETE_TYPE_P (expr_type))
+	inform (DECL_SOURCE_LOCATION (TYPE_MAIN_DECL (expr_type)),
+		"class type %qT is incomplete", expr_type);
+    }
   return error_mark_node;
 }
 

gcc/testsuite/g++.dg/expr/static_cast8.C

+// PR c++/52321
+struct A1; // { dg-message "note: class type 'A1' is incomplete" }
+struct A2; // { dg-message "note: class type 'A2' is incomplete" }
+struct B1; // { dg-message "note: class type 'B1' is incomplete" }
+struct B2; // { dg-message "note: class type 'B2' is incomplete" }
+
+struct C { };
+extern C* c;
+
+void pointers(C* c, A2* a2, B1* b1)
+{
+  (void) static_cast<A1*>(c);	// { dg-error "invalid static_cast" }
+  (void) static_cast<C*>(a2);	// { dg-error "invalid static_cast" }
+  (void) static_cast<B2*>(b1);	// { dg-error "invalid static_cast" }
+}
+
+struct D1; // { dg-message "note: class type 'D1' is incomplete" }
+struct D2; // { dg-message "note: class type 'D2' is incomplete" }
+struct E1; // { dg-message "note: class type 'E1' is incomplete" }
+struct E2; // { dg-message "note: class type 'E2' is incomplete" }
+
+void references(C& c, D2& d2, E1& e1)
+{
+  (void) static_cast<D1&>(c);	// { dg-error "invalid static_cast" }
+  (void) static_cast<C&>(d2);	// { dg-error "invalid static_cast" }
+  (void) static_cast<E2&>(e1);	// { dg-error "invalid static_cast" }
+}