merge revision(s) 6b66b5fdedb2c9a9ee48e290d57ca7f8d55e01a2: [Backport #19902]

	[Bug #19902] Update the coderange regarding the changed region

	---
	 ext/-test-/string/set_len.c       | 10 ++++++++++
	 string.c                          | 27 +++++++++++++++++++++++++++
	 test/-ext-/string/test_set_len.rb | 29 +++++++++++++++++++++++++++++
	 3 files changed, 66 insertions(+)

1 files changed, 29 insertions, 0 deletions

diff --git a/test/-ext-/string/test_set_len.rb b/test/-ext-/string/test_set_len.rb
index 67ba961194..e3eff75d9b 100644
--- a/test/-ext-/string/test_set_len.rb
+++ b/test/-ext-/string/test_set_len.rb
@@ -34,4 +34,33 @@ class Test_StrSetLen < Test::Unit::TestCase
     assert_equal 128, Bug::String.capacity(str)
     assert_equal 127, str.set_len(127).bytesize, bug12757
   end
+
+  def test_coderange_after_append
+    u = -"\u3042"
+    str = Bug::String.new(encoding: Encoding::UTF_8)
+    bsize = u.bytesize
+    str.append(u)
+    assert_equal 0, str.bytesize
+    str.set_len(bsize)
+    assert_equal bsize, str.bytesize
+    assert_predicate str, :valid_encoding?
+    assert_not_predicate str, :ascii_only?
+    assert_equal u, str
+  end
+
+  def test_coderange_after_trunc
+    u = -"\u3042"
+    bsize = u.bytesize
+    str = Bug::String.new(u)
+    str.set_len(bsize - 1)
+    assert_equal bsize - 1, str.bytesize
+    assert_not_predicate str, :valid_encoding?
+    assert_not_predicate str, :ascii_only?
+    str.append(u.byteslice(-1))
+    str.set_len(bsize)
+    assert_equal bsize, str.bytesize
+    assert_predicate str, :valid_encoding?
+    assert_not_predicate str, :ascii_only?
+    assert_equal u, str
+  end
 end