string.c: fix scanned substring with `\K`

* string.c (scan_once): fix the matched substring with `\K`, the
  beginning of that string may differ from the matched position.
  [ruby-core:86663] [Bug #14707]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63252 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

2 files changed, 3 insertions, 0 deletions

diff --git a/string.c b/string.c
index ad9ba6f355..f989466d32 100644
--- a/string.c
+++ b/string.c
@@ -9046,6 +9046,7 @@ scan_once(VALUE str, VALUE pat, long *start, int set_backref_str)
 	else {
 	    match = rb_backref_get();
 	    regs = RMATCH_REGS(match);
+	    pos = BEG(0);
 	    end = END(0);
 	}
 	if (pos == end) {
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index d6356fcfa1..1a6d87f11f 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -1542,6 +1542,8 @@ CODE
     assert_nil($~)
 
     assert_equal(3, S("hello hello hello").scan("hello".taint).count(&:tainted?))
+
+    assert_equal(%w[1 2 3], S("a1 a2 a3").scan(/a\K./))
   end
 
   def test_size