nobu	2013-11-10 22:16:33 +0900 (Sun, 10 Nov 2013)

  New Revision: 43636

  http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=rev&revision=43636

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

  Modified files:
    trunk/ChangeLog
    trunk/error.c
    trunk/eval.c
    trunk/test/ruby/test_exception.rb
Index: ChangeLog
===================================================================
--- ChangeLog	(revision 43635)
+++ ChangeLog	(revision 43636)
@@ -1,3 +1,10 @@ https://github.com/ruby/ruby/blob/trunk/ChangeLog#L1
+Sun Nov 10 22:16:19 2013  Nobuyoshi Nakada  <nobu@r...>
+
+	* 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@z...>
 
 	* thread.c: [DOC] Remove duplicate reference
Index: eval.c
===================================================================
--- eval.c	(revision 43635)
+++ eval.c	(revision 43636)
@@ -641,6 +641,10 @@ make_exception(int argc, VALUE *argv, in https://github.com/ruby/ruby/blob/trunk/eval.c#L641
 	if (argc > 2)
 	    set_backtrace(mesg, argv[2]);
     }
+    {
+	VALUE cause = get_errinfo();
+	if (!NIL_P(cause)) rb_iv_set(mesg, "cause", cause);
+    }
 
     return mesg;
 }
Index: error.c
===================================================================
--- error.c	(revision 43635)
+++ error.c	(revision 43636)
@@ -780,6 +780,14 @@ rb_exc_set_backtrace(VALUE exc, VALUE bt https://github.com/ruby/ruby/blob/trunk/error.c#L780
     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) https://github.com/ruby/ruby/blob/trunk/error.c#L1750
     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);
Index: test/ruby/test_exception.rb
===================================================================
--- test/ruby/test_exception.rb	(revision 43635)
+++ test/ruby/test_exception.rb	(revision 43636)
@@ -476,4 +476,19 @@ end.join https://github.com/ruby/ruby/blob/trunk/test/ruby/test_exception.rb#L476
   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

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