Add --version flag and version subcommand

Prints bootsnap version

lib/bootsnap/cli.rb

@@ -21,20 +21,35 @@ def match?(string)
 
     attr_reader :cache_dir, :argv
 
-    attr_accessor :compile_gemfile, :exclude, :verbose, :iseq, :yaml, :json, :jobs
+    attr_accessor(
+      :compile_gemfile,
+      :exclude,
+      :verbose,
+      :iseq,
+      :yaml,
+      :json,
+      :jobs,
+      :version
+    )
 
     def initialize(argv)
       @argv = argv
       self.cache_dir = ENV.fetch("BOOTSNAP_CACHE_DIR", "tmp/cache")
       self.compile_gemfile = false
       self.exclude = nil
       self.verbose = false
+      self.version = false
       self.jobs = Etc.nprocessors
       self.iseq = true
       self.yaml = true
       self.json = true
     end
 
+    def version_command
+      puts Bootsnap::VERSION
+      0
+    end
+
     def precompile_command(*sources)
       require "bootsnap/compile_cache"
 
@@ -113,7 +128,7 @@ def list_files(path, pattern)
     def run
       parser.parse!(argv)
       command = argv.shift
-      method = "#{command}_command"
+      method = version ? "version_command" : "#{command}_command"
       if respond_to?(method)
         public_send(method, *argv)
       else
@@ -227,6 +242,13 @@ def parser
         opts.separator "GLOBAL OPTIONS"
         opts.separator ""
 
+        help = <<~HELP
+          Prints the version of bootsnap
+        HELP
+        opts.on("--version", help.strip) do
+          self.version = true
+        end
+
         help = <<~HELP
           Path to the bootsnap cache directory. Defaults to tmp/cache
         HELP
@@ -252,6 +274,7 @@ def parser
         opts.separator "COMMANDS"
         opts.separator ""
         opts.separator "    precompile [DIRECTORIES...]: Precompile all .rb files in the passed directories"
+        opts.separator "    version: Prints the version of bootsnap"
 
         help = <<~HELP
           Precompile the gems in Gemfile

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
 
+    def test_version
+      out, err = capture_io do
+        assert_equal 0, CLI.new(["version"]).run
+      end
+
+      assert_equal Bootsnap::VERSION + "\n", out
+      assert_equal "", err
+    end
+
+    def test_version_flag
+      out, err = capture_io do
+        assert_equal 0, CLI.new(["--version"]).run
+      end
+
+      assert_equal Bootsnap::VERSION + "\n", out
+      assert_equal "", err
+    end
+
     private
 
     def skip_unless_iseq