error.c: check redefined backtrace result

* error.c (rb_get_backtrace): check the result of `backtrace` even
  if the method is redefined.  [ruby-core:87013] [Bug #14756]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63417 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

error.c

@@ -1162,19 +1162,21 @@ VALUE
 rb_get_backtrace(VALUE exc)
 {
     ID mid = id_backtrace;
+    VALUE info;
     if (rb_method_basic_definition_p(CLASS_OF(exc), id_backtrace)) {
-	VALUE info, klass = rb_eException;
+	VALUE klass = rb_eException;
 	rb_execution_context_t *ec = GET_EC();
 	if (NIL_P(exc))
 	    return Qnil;
 	EXEC_EVENT_HOOK(ec, RUBY_EVENT_C_CALL, exc, mid, mid, klass, Qundef);
 	info = exc_backtrace(exc);
 	EXEC_EVENT_HOOK(ec, RUBY_EVENT_C_RETURN, exc, mid, mid, klass, info);
-	if (NIL_P(info))
-	    return Qnil;
-	return rb_check_backtrace(info);
     }
-    return rb_funcallv(exc, mid, 0, 0);
+    else {
+	info = rb_funcallv(exc, mid, 0, 0);
+    }
+    if (NIL_P(info)) return Qnil;
+    return rb_check_backtrace(info);
 }
 
 /*

test/ruby/test_exception.rb

@@ -1236,6 +1236,16 @@ $stderr = $stdout; raise "\x82\xa0"') do |outs, errs, status|
         raise RuntimeError, "hello"
       }
     end;
+
+    error_class = Class.new(StandardError) do
+      def backtrace; :backtrace; end
+    end
+    begin
+      raise error_class
+    rescue error_class => e
+      assert_raise(TypeError) {$@}
+      assert_raise(TypeError) {e.full_message}
+    end
   end
 
   def test_backtrace_in_eval