Make rpartition compatible with Ruby 2.7

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

@@ -11,6 +11,18 @@
     "hello".rpartition("hello").should == ["", "hello", ""]
   end
 
+  it "returns original string if regexp doesn't match" do
+    "hello".rpartition("/x/").should == ["", "", "hello"]
+  end
+
+  it "returns new object if doesn't match" do
+    "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

@@ -203,9 +203,9 @@ 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)
-        [m.pre_match, m[0], m.post_match]
+        return [m.pre_match, m[0], m.post_match]
       end
     else
       pattern = StringValue(pattern)
@@ -217,11 +217,11 @@ def rpartition(pattern)
                 pattern.dup,
                 Primitive.string_substring(self, post_start, post_len)]
       end
-
-      # Nothing worked out, this is the default.
-      empty = String.new(encoding: encoding)
-      [empty, empty.dup, self]
     end
+
+    # Nothing worked out, this is the default.
+    empty = String.new(encoding: encoding)
+    [empty, empty.dup, self.dup]
   end
 
   def rstrip

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"