Add --version flag

Fix: #483

lib/bootsnap/cli.rb

@@ -222,6 +222,9 @@ def exclude_pattern(pattern)
 
     def parser
       @parser ||= OptionParser.new do |opts|
+        opts.version = Bootsnap::VERSION
+        opts.program_name = "bootsnap"
+
         opts.banner = "Usage: bootsnap COMMAND [ARGS]"
         opts.separator ""
         opts.separator "GLOBAL OPTIONS"

test/cli_test.rb

@@ -75,6 +75,24 @@ def test_no_yaml
       assert_equal 0, CLI.new(["precompile", "-j", "0", "--no-yaml", path]).run
     end
 
+    if Process.respond_to?(:fork)
+      def test_version_flag
+        read, write = IO.pipe
+        # optparse --version immediately call exit so we test in a subprocess
+        pid = fork do 
+          STDOUT.reopen(write)
+          read.close
+          exit(CLI.new(["--version"]).run)
+        end
+        write.close
+
+        _, status = Process.waitpid2(pid)
+        assert_predicate status, :success?
+
+        assert_includes read.read, Bootsnap::VERSION
+      end
+    end
+
     private
 
     def skip_unless_iseq