[GR-18163] Return new String instances from File.basename

PullRequest: truffleruby/2631

Author: eregon

CHANGELOG.md

@@ -23,6 +23,7 @@ Compatibility:
 * Configure `mandir` value in `RbConfig::CONFIG` and `RbConfig::MAKEFILE_CONFIG` (#2315).
 * TruffleRuby now supports the Truffle polyglot Hash interop API.
 * Implement `Fiber#raise` (#2338).
+* Update `File.basename` to return new `String` instances (#2343).
 
 Performance:
 

spec/ruby/core/file/basename_spec.rb

@@ -164,5 +164,20 @@
     basename.encoding.should == Encoding::Windows_1250
   end
 
+  it "returns a new unfrozen String" do
+    exts = [nil, '.rb', '.*', '.txt']
+    ['foo.rb','//', '/test/', 'test'].each do |example|
+      exts.each do |ext|
+        original = example.freeze
+        result = if ext
+                   File.basename(original, ext)
+                 else
+                   File.basename(original)
+                 end
+        result.should_not equal(original)
+        result.frozen?.should == false
+      end
+    end
+  end
 
 end

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

@@ -183,20 +183,20 @@ def self.basename(path, ext=undefined)
         end
 
         # edge case, it's all /'s, return "/"
-        return slash unless found
+        return slash.dup unless found
 
         # Now that we've trimmed the /'s at the end, search again
         pos = Primitive.find_string_reverse(path, slash, path.bytesize)
         if ext_not_present and !pos
           # No /'s found and ext not present, return path.
-          return path
+          return path.dup
         end
       end
 
       path = path.byteslice(pos + 1, path.bytesize - pos) if pos
     end
 
-    return path if ext_not_present
+    return path.dup if ext_not_present
 
     # special case. if ext is ".*", remove any extension
 
@@ -213,7 +213,7 @@ def self.basename(path, ext=undefined)
       end
     end
 
-    path
+    path.dup
   end
 
   def self.query_stat_mode(path)