merge revision(s) 564ccd095a9d7fbe869031dbf666d61dadfdcb03: [Backport #17756]

	[ruby/strscan] Fix segmentation fault of `StringScanner#charpos` when
	 `String#byteslice` returns non string value [Bug #17756] (#20)

	https://github.com/ruby/strscan/commit/92961cde2b
	---
	 ext/strscan/strscan.c              |  5 +----
	 test/strscan/test_stringscanner.rb | 17 +++++++++++++++++
	 2 files changed, 18 insertions(+), 4 deletions(-)

1 files changed, 17 insertions, 0 deletions

diff --git a/test/strscan/test_stringscanner.rb b/test/strscan/test_stringscanner.rb
index 4b001b317e..6e30be1f7d 100644
--- a/test/strscan/test_stringscanner.rb
+++ b/test/strscan/test_stringscanner.rb
@@ -206,6 +206,23 @@ class TestStringScanner < Test::Unit::TestCase
     assert_equal 11, s.charpos
   end
 
+  def test_charpos_not_use_string_methods
+    string = +'abcädeföghi'
+    scanner = create_string_scanner(string)
+
+    class << string
+      EnvUtil.suppress_warning do
+        undef_method(*instance_methods)
+      end
+    end
+
+    assert_equal 0, scanner.charpos
+    assert_equal "abcä", scanner.scan_until(/ä/)
+    assert_equal 4, scanner.charpos
+    assert_equal "defö", scanner.scan_until(/ö/)
+    assert_equal 8, scanner.charpos
+  end
+
   def test_concat
     s = create_string_scanner('a'.dup)
     s.scan(/a/)