Add File#rename

spec/std/file_spec.cr

@@ -604,6 +604,16 @@ describe "File" do
         end
       end
     end
+
+    it "renames a File instance" do
+      with_tempfile("rename-source.txt", "rename-target.txt") do |source_path, target_path|
+        f = File.new(source_path, "w")
+        f.rename target_path
+        f.path.should eq target_path
+        File.exists?(source_path).should be_false
+        File.exists?(target_path).should be_true
+      end
+    end
   end
 
   # There are more detailed specs for `Path#expand` in path_spec.cr

src/file.cr

@@ -866,6 +866,12 @@ class File < IO::FileDescriptor
     end
   end
 
+  # Rename the current `File`
+  def rename(new_filename : Path | String) : Nil
+    File.rename(@path, new_filename)
+    @path = new_filename.to_s
+  end
+
   # Sets the access and modification times of *filename*.
   #
   # Use `#utime` if the `File` is already open.