error.c: Exception#cause

* error.c (exc_cause): captured previous exception.
* eval.c (make_exception): capture previous exception automagically.
  [Feature #8257]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43636 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,10 @@
+Sun Nov 10 22:16:19 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* error.c (exc_cause): captured previous exception.
+
+	* eval.c (make_exception): capture previous exception automagically.
+	  [Feature #8257]
+
 Sun Nov 10 08:37:20 2013  Zachary Scott  <e@zzak.io>
 
 	* thread.c: [DOC] Remove duplicate reference

error.c

@@ -780,6 +780,14 @@ rb_exc_set_backtrace(VALUE exc, VALUE bt)
     return exc_set_backtrace(exc, bt);
 }
 
+VALUE
+exc_cause(VALUE exc)
+{
+    ID id_cause;
+    CONST_ID(id_cause, "cause");
+    return rb_attr_get(exc, id_cause);
+}
+
 static VALUE
 try_convert_to_exception(VALUE obj)
 {
@@ -1742,6 +1750,7 @@ Init_Exception(void)
     rb_define_method(rb_eException, "inspect", exc_inspect, 0);
     rb_define_method(rb_eException, "backtrace", exc_backtrace, 0);
     rb_define_method(rb_eException, "set_backtrace", exc_set_backtrace, 1);
+    rb_define_method(rb_eException, "cause", exc_cause, 0);
 
     rb_eSystemExit  = rb_define_class("SystemExit", rb_eException);
     rb_define_method(rb_eSystemExit, "initialize", exit_initialize, -1);

eval.c

@@ -641,6 +641,10 @@ make_exception(int argc, VALUE *argv, int isstr)
 	if (argc > 2)
 	    set_backtrace(mesg, argv[2]);
     }
+    {
+	VALUE cause = get_errinfo();
+	if (!NIL_P(cause)) rb_iv_set(mesg, "cause", cause);
+    }
 
     return mesg;
 }

test/ruby/test_exception.rb

@@ -476,4 +476,19 @@ end.join
   def test_stackoverflow
     assert_raise(SystemStackError){m}
   end
+
+  def test_cause
+    msg = "[Feature #8257]"
+    e = assert_raise(StandardError) {
+      begin
+        raise msg
+      rescue => e
+        assert_nil(e.cause, msg)
+        raise StandardError
+      end
+    }
+    cause = e.cause
+    assert_instance_of(RuntimeError, cause, msg)
+    assert_equal(msg, cause.message, msg)
+  end
 end