Fix multibyte handling

CHANGELOG.md

@@ -9,6 +9,7 @@ Bug fixes:
 Compatibility:
 
 * Make interpolated strings frozen for compatibility with Ruby 2.7 (#2304, @kirs).
+* Make rpartition compatible with Ruby 2.7 (#2320, @gogainda).
 
 Performance:
 

spec/ruby/core/string/rpartition_spec.rb

@@ -19,6 +19,10 @@
     "hello".rpartition("/no_match/").last.object_id.should_not eql("hello".object_id)
   end
 
+  it "handles multibyte string correctly" do
+    "ユーザ@ドメイン".rpartition(/@/).should == ["ユーザ", "@", "ドメイン"]
+  end
+
   it "accepts regexp" do
     "hello!".rpartition(/l./).should == ["hel", "lo", "!"]
   end

src/main/ruby/truffleruby/core/string.rb

@@ -203,7 +203,7 @@ def partition(pattern=nil)
 
   def rpartition(pattern)
     if pattern.kind_of? Regexp
-      if m = Truffle::RegexpOperations.search_region(pattern, self, 0, size, false)
+      if m = Truffle::RegexpOperations.search_region(pattern, self, 0, bytesize, false)
         Primitive.regexp_last_match_set(Primitive.caller_special_variables, m)
         return [m.pre_match, m[0], m.post_match]
       end

test/mri/excludes/TestString.rb

@@ -14,7 +14,6 @@
 exclude :test_lines, "needs investigation"
 exclude :test_partition, "needs investigation"
 exclude :test_respond_to, "needs investigation"
-exclude :test_rpartition, "needs investigation"
 exclude :test_rstrip, "needs investigation"
 exclude :test_rstrip_bang, "needs investigation"
 exclude :test_setter, "needs investigation"