range.c: return nil for empty range

* range.c (range_last): return nil for empty range, or in the case the
  predecessor is smaller than the begin.  [Bug #8739]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42407 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Tue Aug  6 21:59:56 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* range.c (range_last): return nil for empty range, or in the case the
+	  predecessor is smaller than the begin.  [Bug #8739]
+
 Tue Aug  6 21:48:31 2013  Kouji Takao  <kouji.takao@gmail.com>
 
 	* ext/readline/readline.c (readline_s_set_point, Init_readline):

range.c

@@ -891,8 +891,15 @@ range_last(int argc, VALUE *argv, VALUE range)
 	VALUE e = RANGE_END(range);
 	if (!EXCL(range)) return e; /* inclusive, the end is the last */
 	/* exclusive, the last is previous to the end */
-	if (FIXNUM_P(e) || rb_obj_is_kind_of(e, rb_cNumeric))
+	if (FIXNUM_P(e) || rb_obj_is_kind_of(e, rb_cNumeric)) {
-	    return rb_int_pred(e);
+	    VALUE pred = rb_int_pred(e);
+	    if (!r_lt(RANGE_BEG(range), pred)) {
+		/* TODO: what should be returned, or should raise an
+		 * exception? */
+		pred = Qnil;
+	    }
+	    return pred;
+	}
 
 	/* fallback to Array */
     }

test/ruby/test_range.rb

@@ -254,6 +254,7 @@ class TestRange < Test::Unit::TestCase
     assert_equal(10, (0..10).last)
     assert_equal("a", ("a".."c").first)
     assert_equal("c", ("a".."c").last)
+    assert_equal(0, (2..0).last)
 
     bug8739 = '[ruby-dev:47587] [Bug #8739] from exclusive range'
     assert_equal([0, 1, 2], (0...10).first(3), bug8739)
@@ -262,6 +263,7 @@ class TestRange < Test::Unit::TestCase
     assert_equal(9, (0...10).last, bug8739)
     assert_equal("a", ("a"..."c").first, bug8739)
     assert_equal("b", ("a"..."c").last, bug8739)
+    assert_nil((2...0).last)
   end
 
   def test_to_s