Fix Racc::ParseError so Pattern Matching is supported

首先，将提供的复现代码保存为 snippet.rb，并使用 Ruby 2.7.2 运行它，以确认与模式匹配 in 语法相关的 Racc::ParseError。跟踪 Racc 如何处理此输入，并为该示例添加覆盖；完成的标准是该代码片段能够在不出现所报告错误的情况下完成解析。

Overview

When using Flog on a project that uses Ruby Pattern Matching, I get the following error:

 bkuhlmann@vilya  rubysmith  alchemists.io  ⑂ release +    flog
ERROR: parsing ruby file ./lib/rubysmith/cli/shell.rb
ERROR! Aborting. You may want to run with --continue.
Traceback (most recent call last):
	23: from /Users/bkuhlmann/.gem/ruby/2.7.2/bin/flog:23:in `<main>'
	22: from /Users/bkuhlmann/.gem/ruby/2.7.2/bin/flog:23:in `load'
	21: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/flog-4.6.4/bin/flog:5:in `<top (required)>'
	20: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/flog-4.6.4/lib/flog_cli.rb:28:in `run'
	19: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/flog-4.6.4/lib/flog_cli.rb:162:in `flog'
	18: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/flog-4.6.4/lib/flog.rb:177:in `flog'
	17: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/flog-4.6.4/lib/flog.rb:177:in `each'
	16: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/flog-4.6.4/lib/flog.rb:182:in `block in flog'
	15: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/flog-4.6.4/lib/flog.rb:194:in `flog_ruby'
	14: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/flog-4.6.4/lib/flog.rb:224:in `flog_ruby!'
	13: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/ruby_parser-3.15.0/lib/ruby_parser.rb:33:in `process'
	12: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/ruby_parser-3.15.0/lib/ruby_parser.rb:33:in `each'
	11: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/ruby_parser-3.15.0/lib/ruby_parser.rb:36:in `block in process'
	10: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/ruby_parser-3.15.0/lib/ruby_parser_extras.rb:1317:in `process'
	 9: from /Users/bkuhlmann/.rubies/ruby-2.7.2/lib/ruby/2.7.0/timeout.rb:110:in `timeout'
	 8: from /Users/bkuhlmann/.rubies/ruby-2.7.2/lib/ruby/2.7.0/timeout.rb:33:in `catch'
	 7: from /Users/bkuhlmann/.rubies/ruby-2.7.2/lib/ruby/2.7.0/timeout.rb:33:in `catch'
	 6: from /Users/bkuhlmann/.rubies/ruby-2.7.2/lib/ruby/2.7.0/timeout.rb:33:in `block in catch'
	 5: from /Users/bkuhlmann/.rubies/ruby-2.7.2/lib/ruby/2.7.0/timeout.rb:95:in `block in timeout'
	 4: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/ruby_parser-3.15.0/lib/ruby_parser_extras.rb:1329:in `block in process'
	 3: from (eval):3:in `do_parse'
	 2: from (eval):3:in `_racc_do_parse_c'
	 1: from /Users/bkuhlmann/.gem/ruby/2.7.2/gems/ruby_parser-3.15.0/lib/ruby_parser_extras.rb:1304:in `on_error'
/Users/bkuhlmann/.gem/ruby/2.7.2/gems/racc-1.5.1/lib/racc/parser.rb:538:in `on_error': ./lib/rubysmith/cli/shell.rb:27 :: parse error on value ["in", 27] (kIN) (Racc::ParseError)

Steps to Recreate

To recreate, I'm using Flog to illustrate since Flog has Racc as a dependency. Save the following to snippet.rb and run as ruby snippet.rb to see the issue:

# frozen_string_literal: true

require "bundler/inline"

gemfile true do
  source "https://rubygems.org"
  gem "flog", "~> 4.6"
end

collection = {
  a: 1,
  b: 2
}

case collection
  in a: value then puts value
  in b: value then puts value
end

Desired Behavior

Would like to see Racc handle pattern matching without error.

Environment

ruby -v
ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-darwin19]