Add a simple tool to synchronize changes from Ruby source files to the GraalVM build

PullRequest: truffleruby/671

Author: eregon

tool/jt.rb

@@ -593,6 +593,7 @@ def help
       jt install jvmci                              install a JVMCI JDK in the parent directory
       jt install graal [--no-jvmci]                 install Graal in the parent directory (--no-jvmci to use the system Java)
       jt docker                                     build a Docker image - see doc/contributor/docker.md
+      jt sync                                       continuously synchronize changes from the Ruby source files to the GraalVM build
 
       you can also put --build or --rebuild in front of any command to build or rebuild first
 
@@ -2097,6 +2098,10 @@ def verify_native_bin!
   end
   private :verify_native_bin!
 
+  def sync
+    exec(RbConfig.ruby, "#{TRUFFLERUBY_DIR}/tool/sync.rb")
+  end
+
   def docker(*args)
     command = args.shift
     case command

tool/sync.rb

@@ -0,0 +1,42 @@
+#!/usr/bin/env ruby
+
+# Copyright (c) 2019 Oracle and/or its affiliates. All rights reserved.
+# This code is released under a tri EPL/GPL/LGPL license. You can use it,
+# redistribute it and/or modify it under the terms of the:
+#
+# Eclipse Public License version 1.0, or
+# GNU General Public License version 2, or
+# GNU Lesser General Public License version 2.1.
+
+# A script to synchronize changes from the Ruby source files
+# to the GraalVM build instantaneously.
+
+# Use 'gem install listen' to install this dependency
+require 'listen'
+
+require 'fileutils'
+
+FROM = File.expand_path('../..', File.realpath(__FILE__))
+TO = "#{FROM}/mxbuild/graalvm/jre/languages/ruby"
+
+# Must be consistent with TRUFFLERUBY_GRAALVM_SUPPORT in suite.py
+DIRS_TO_SYNC = %w[
+  lib/json
+  lib/mri
+  lib/patches
+  lib/truffle
+].map { |path| "#{FROM}/#{path}" }
+
+listener = Listen.to(*DIRS_TO_SYNC) do |modified, added, removed|
+  (modified + added).each do |file|
+    target = "#{TO}#{file[FROM.size..-1]}"
+    FileUtils::Verbose.cp file, target
+  end
+  removed.each do |file|
+    target = "#{TO}#{file[FROM.size..-1]}"
+    FileUtils::Verbose.rm target
+  end
+end
+
+listener.start # not blocking
+sleep