# DeadEnd An error in your code forces you to stop. DeadEnd helps you find those errors to get you back on your way faster. ``` Unmatched `end', missing keyword (`do', `def`, `if`, etc.) ? 1 class Dog ❯ 2 defbark ❯ 4 end 5 end ``` ## Installation in your codebase To automatically annotate errors when they happen, add this to your Gemfile: ```ruby gem 'dead_end' ``` And then execute: $ bundle install If your application is not calling `Bundler.require` then you must manually add a require: ```ruby require "dead_end" ``` If you're using rspec add this to your `.rspec` file: ``` --require dead_end ``` > This is needed because people can execute a single test file via `bundle exec rspec path/to/file_spec.rb` and if that file has a syntax error, it won't load `spec_helper.rb` to trigger any requires. ## Install the CLI To get the CLI and manually search for syntax errors (but not automatically annotate them), you can manually install the gem: $ gem install dead_end This gives you the CLI command `$ dead_end` for more info run `$ dead_end --help`. ## Editor integration An extension is available for VSCode: - Extension: https://marketplace.visualstudio.com/items?itemName=Zombocom.dead-end-vscode - GitHub: https://github.com/zombocom/dead_end-vscode ## What syntax errors does it handle? Dead end will fire against all syntax errors and can isolate any syntax error. In addition, dead_end attempts to produce human readable descriptions of what needs to be done to resolve the issue. For example: - Missing `end`: ``` Unmatched keyword, missing `end' ? ❯ 1 class Dog ❯ 2 def bark ❯ 4 end ``` - Missing keyword ``` Unmatched `end', missing keyword (`do', `def`, `if`, etc.) ? 1 class Dog 2 def speak ❯ 3 @sounds.each |sound| ❯ 5 end 6 end 7 end ``` - Missing pair characters (like `{}`, `[]`, `()` , or `||`) ``` Unmatched `(', missing `)' ? 1 class Dog ❯ 2 def speak(sound ❯ 4 end 5 end ``` - Any ambiguous or unknown errors will be annotated by the original ripper error output: ``` syntax error, unexpected end-of-input 1 class Dog 2 def meals_last_month ❯ 3 puts 3 * 4 end 5 end ``` ## How is it better than `ruby -wc`? Ruby allows you to syntax check a file with warnings using `ruby -wc`. This emits a parser error instead of a human focused error. Ruby's parse errors attempt to narrow down the location and can tell you if there is a glaring indentation error involving `end`. The `dead_end` algorithm doesn't just guess at the location of syntax errors, it re-parses the document to prove that it captured them. This library focuses on the human side of syntax errors. It cares less about why the document could not be parsed (computer problem) and more on what the programmer needs (human problem) to fix the problem. ## Sounds cool, but why isn't this baked into Ruby directly? We are now talking about it https://bugs.ruby-lang.org/issues/18159#change-93682. ## Artificial Inteligence? This library uses a goal-seeking algorithm for syntax error detection similar to that of a path-finding search. For more information [read the blog post about how it works under the hood](https://schneems.com/2020/12/01/squash-unexpectedend-errors-with-syntaxsearch/). ## How does it detect syntax error locations? We know that source code that does not contain a syntax error can be parsed. We also know that code with a syntax error contains both valid code and invalid code. If you remove the invalid code, then we can programatically determine that the code we removed contained a syntax error. We can do this detection by generating small code blocks and searching for which blocks need to be removed to generate valid source code. Since there can be multiple syntax errors in a document it's not good enough to check individual code blocks, we've got to check multiple at the same time. We will keep creating and adding new blocks to our search until we detect that our "frontier" (which contains all of our blocks) contains the syntax error. After this, we can stop our search and instead focus on filtering to find the smallest subset of blocks that contain the syntax error. Here's an example: ![](assets/syntax_search.gif) ## Use internals To use the `dead_end` gem without monkeypatching you can `require 'dead_end/api'`. This will allow you to load `dead_end` and use its internals without mutating `require`. Stable internal interface(s): - `DeadEnd.handle_error(e)` Any other entrypoints are subject to change without warning. If you want to use an internal interface from `dead_end` not on this list, open an issue to explain your use case. ## Development After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment. To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org). ### How to debug changes to output display You can see changes to output against a variety of invalid code by running specs and using the `DEBUG_DISPLAY=1` environment variable. For example: ``` $ DEBUG_DISPLAY=1 bundle exec rspec spec/ --format=failures ``` ### Run profiler You can output profiler data to the `tmp` directory by running: ``` $ DEBUG_PERF=1 bundle exec rspec spec/integration/dead_end_spec.rb ``` Some outputs are in text format, some are html, the raw marshaled data is available in `raw.rb.marshal`. See https://ruby-prof.github.io/#reports for more info. One interesting one, is the "kcachegrind" interface. To view this on mac: ``` $ brew install qcachegrind ``` Open: ``` $ qcachegrind tmp/last/profile.callgrind.out. ``` ## Contributing Bug reports and pull requests are welcome on GitHub at https://github.com/zombocom/dead_end. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [code of conduct](https://github.com/zombocom/dead_end/blob/main/CODE_OF_CONDUCT.md). ## License The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT). ## Code of Conduct Everyone interacting in the DeadEnd project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the [code of conduct](https://github.com/zombocom/dead_end/blob/main/CODE_OF_CONDUCT.md).