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# Ruby Next
Ruby Next is a **transpiler** and a collection of **polyfills** for supporting the latest and upcoming Ruby features (APIs and syntax) in older versions and alternative implementations. For example, you can use pattern matching and `Kernel#then` in Ruby 2.5 or [mruby][].
Who might be interested in Ruby Next?
- **Ruby gems maintainers** who want to write code using the latest Ruby version but still support older ones.
- **Application developers** who want to give new features a try without waiting for the final release (or, more often, for the first patch).
- **Users of non-MRI implementations** such as [mruby][], [JRuby][], [TruffleRuby][], [Opal][], [RubyMotion][], [Artichoke][], [Prism][].
Ruby Next also aims to help the community to assess new, _experimental_, MRI features by making it easier to play with them.
That's why Ruby Next implements the `master` features as fast as possible.
## Links
- [Ruby Next: Make old Rubies quack like a new one](https://noti.st/palkan/j3i2Dr/ruby-next-make-old-rubies-quack-like-a-new-one) (RubyConf 2019)
## Table of contents
- [Overview](#overview)
- [Quick Start](#quick-start)
- [Polyfills](#using-only-polyfills)
- [Transpiling](#transpiling)
- [Modes](#transpiler-modes)
- [CLI](#cli)
- [Using in gems](#integrating-into-a-gem-development)
- [Runtime usage](#runtime-usage)
- [Bootsnap integration](#using-with-bootsnap)
- [`ruby -ruby-next`](#uby-next)
- [Logging & Debugging](#logging-and-debugging)
- [RuboCop](#rubocop)
- [Proposed & edge features](#proposed-and-edge-features)
## Overview
Ruby Next consists of two parts: **core** and **language**.
Core provides **polyfills** for Ruby core classes APIs via Refinements (default strategy) or core extensions (optionally or for refinement-less environments).
Language is responsible for **transpiling** edge Ruby syntax into older versions. It could be done
programmatically or via CLI. It also could be done in runtime.
Currently, Ruby Next supports Ruby versions 2.5+ (including JRuby 9.2.8+).
Please, [open an issue](https://github.com/ruby-next/ruby-next/issues/new/choose) if you would like us to support older Ruby versions.
## Quick start
The quickest way to start experimenting with Ruby Next is to install the gem and run a sample script. For example:
```sh
# Install Ruby Next globally
$ gem install ruby-next
# Call ruby with -ruby-next flag
$ ruby -ruby-next -e "
case {hello: 'martian'}
in hello: hello if hello =~ /human/
puts '🙂'
in hello: 'martian'
puts '👽'
end
"
=> 👽
```
## Using only polyfills
First, install a gem:
```ruby
# Gemfile
gem "ruby-next-core"
# gemspec
spec.add_dependency "ruby-next-core"
```
**NOTE:** we use the different _distribution_ gem, `ruby-next-core`, to provide zero-dependency, polyfills-only version.
Then, all you need is to load the Ruby Next:
```ruby
require "ruby-next"
```
And activate the refinement in every file where you want to use it\*:
```ruby
using RubyNext
```
Ruby Next only refines core classes if necessary; thus, this line wouldn't have any effect in the edge Ruby.
**NOTE:** Even if the runtime already contains a monkey-patch with the backported functionality, we consider the method as _dirty_ and activate the refinement for it. Thus, you always have predictable behaviour. That's why we recommend using refinements for gems development.
Alternatively, you can go with monkey-patches. Just add this line:
```ruby
require "ruby-next/core_ext"
```
The following _rule of thumb_ is recommended when choosing between refinements and monkey-patches:
- Use refinements for libraries development (to avoid conflicts with others code)
- Using core extensions could be considered for application development (no need to think about `using RubyNext`); this approach could potentially lead to conflicts with dependencies (if these dependencies are not using refinements 🙂)
- Use core extensions if refinements are not supported by your platform
[**The list of supported APIs.**][features_core]
## Transpiling
Ruby Next allows you to transpile\* edge Ruby syntax to older versions.
Transpiler relies on two libraries: [parser][] and [unparser][].
**NOTE:** The "official" parser gem only supports the latest stable Ruby version, while Ruby Next aims to support edge and experimental Ruby features. To enable them, you should use our version of Parser (see [instructions](#using-ruby-next-parser) below).
Installation:
```ruby
# Gemfile
gem "ruby-next"
# gemspec
spec.add_dependency "ruby-next"
```
```sh
# or install globally
gem install ruby-next
```
[**The list of supported syntax features.**][features_syntax]
### Transpiler modes
Ruby Next currently provides two different modes of generating transpiled code: _AST_ and _rewrite_.
In the AST mode, we parse the source code into AST, modifies this AST and **generate a new code from AST** (using [unparser][unparser]). Thus, the transpiled code being identical in terms of functionality has different formatting.
In the rewrite mode, we apply changes to the source code itself, thus, keeping the original formatting of the unaffected code (in a similar way to RuboCop's autocorrect feature).
By default, we use the AST mode. That could likely change in the future when we collect enough feedback on the rewrite mode and fix potential bugs.
The main benefit of the rewrite mode is that it preserves the original code line numbers and layout, which is especially useful in debugging.
You can change the transpiler mode:
- From code by setting `RubyNext::Language.mode = :ast` or `RubyNext::Language.mode = :rewrite`.
- Via environmental variable `RUBY_NEXT_TRANSPILE_MODE=rewrite`.
- Via CLI option ([see below](#cli)).
## CLI
Ruby Next ships with the command-line interface (`ruby-next`) which provides the following functionality:
### `ruby-next nextify`
This command allows you to transpile a file or directory into older Rubies (see, for example, the "Integrating into a gem development" section above).
It has the following interface:
```sh
$ ruby-next nextify
Usage: ruby-next nextify DIRECTORY_OR_FILE [options]
-o, --output=OUTPUT Specify output directory or file or stdout (use -o stdout for that)
--min-version=VERSION Specify the minimum Ruby version to support
--single-version Only create one version of a file (for the earliest Ruby version)
--enable-method-reference Enable reverted method reference syntax (requires custom parser)
--transpile-mode=MODE Transpiler mode (ast or rewrite). Default: ast
--[no-]refine Do not inject `using RubyNext`
-h, --help Print help
-V Turn on verbose mode
--dry-run Print verbose output without generating files
```
The behaviour depends on whether you transpile a single file or a directory:
- When transpiling a directory, the `.rbnext` subfolder is created within the target folder with subfolders for each supported Ruby versions (e.g., `.rbnext/2.6`, `.rbnext/2.7`). If you want to create only a single version (the smallest), you can also pass `--single-version` flag. In that case, no version directory is created (i.e., transpiled files go into `.rbnext`).
- When transpiling a file and providing the output path as a _file_ path, only a single version is created. For example:
```sh
$ ruby-next nextify my_ruby.rb -o my_ruby_next.rb -V
Ruby Next core strategy: refine
Generated: my_ruby_next.rb
```
### `ruby-next core_ext`
This command could be used to generate a Ruby file with a configurable set of core extensions.
Use this command if you want to backport new Ruby features to Ruby implementations not compatible with RubyGems.
It has the following interface:
```sh
$ ruby-next core_ext
Usage: ruby-next core_ext [options]
-o, --output=OUTPUT Specify output file or stdout (default: ./core_ext.rb)
-l, --list List all available extensions
--min-version=VERSION Specify the minimum Ruby version to support
-n, --name=NAME Filter extensions by name
-h, --help Print help
-V Turn on verbose mode
--dry-run Print verbose output without generating files
```
The most common use-case is to backport the APIs required by pattern matching. You can do this, for example,
by including only monkey-patches containing the `"deconstruct"` in their names:
```sh
ruby-next core_ext -n deconstruct -o pattern_matching_core_ext.rb
```
To list all available (are matching if `--min-version` or `--name` specified) monkey-patches, use the `-l` switch:
```sh
$ ruby-next core_ext -l --name=filter --name=deconstruct
2.6 extensions:
- ArrayFilter
- EnumerableFilter
- HashFilter
2.7 extensions:
- ArrayDeconstruct
- EnumerableFilterMap
- EnumeratorLazyFilterMap
- HashDeconstructKeys
- StructDeconstruct
```
### CLI configuration file
You can define CLI options in the `.rbnextrc` file located in the root of your project to avoid adding them every time you run `ruby-next`.
Configuration file is a YAML with commands as keys and options as multiline strings:
```yml
# ./.rbnextrc
nextify: |
--transpiler-mode=rewrite
--edge
```
## Integrating into a gem development
We recommend _pre-transpiling_ source code to work with older versions before releasing it.
This is how you can do that with Ruby Next:
- Write source code using the modern/edge Ruby syntax.
- Generate transpiled code by calling `ruby-next nextify ./lib` (e.g., before releasing or pushing to VCS).
This will produce `lib/.rbnext` folder containing the transpiled files, `lib/.rbnext/2.6`, `lib/.rbnext/2.7`. The version in the path indicates which Ruby version is required for the original functionality. Only the source files containing new syntax are added to this folder.
**NOTE:** Do not edit these files manually, either run linters/type checkers/whatever against these files.
- Add the following code to your gem's _entrypoint_ (the file that is required first and contains other `require`-s):
```ruby
require "ruby-next/language/setup"
RubyNext::Language.setup_gem_load_path
```
The `setup_gem_load_path` does the following:
- Resolves the current ruby version.
- Checks whether there are directories corresponding to the current and earlier\* Ruby versions within the `.rbnext` folder.
- Add the path to this directory to the `$LOAD_PATH` before the path to the gem's directory.
That's why need an _entrypoint_: all the subsequent `require` calls will load the transpiled files instead of the original ones
due to the way feature resolving works in Ruby (scanning the `$LOAD_PATH` and halting as soon as the matching file is found).
**NOTE:** `require_relative` should be avoided due to the way we _hijack_ the features loading mechanism.
If you're using [runtime mode](#runtime-usage) a long with `setup_gem_load_path` (e.g., in tests), the transpiled files are ignored (i.e., we do not modify `$LOAD_PATH`).
\* Ruby Next avoids storing duplicates; instead, only the code for the earlier version is created and is assumed to be used with other versions. For example, if the transpiled code is the same for Ruby 2.5 and Ruby 2.6, only the `.rbnext/2.7/path/to/file.rb` is kept. That's why multiple entries are added to the `$LOAD_PATH` (`.rbnext/2.6` and `.rbnext/2.7` in the specified order for Ruby 2.5 and only `.rbnext/2.7` for Ruby 2.6).
### Transpiled files vs. VSC vs. installing from source
It's a best practice to not keep generated files in repositories. In case of Ruby Next, it's a `lib/.rbnext` folder.
We recommend adding this folder only to the gem package (i.e., it should be added to your `spec.files`) and ignore it in your VSC (e.g., `echo ".rbnext/" >> .gitignore`). That would make transpiled files available in releases without polluting your repository.
What if someone decides to install your gem from the VSC source? They would likely face some syntax errors due to the missing transpiled files.
To solve this problem, Ruby Next _tries_ to transpile the source code when you call `#setup_gem_load_path`. It does this by calling `bundle exec ruby-next nextify -o `. We make the following assumptions:
- We in the Bundler context (since that's the most common way of installing gems from source).
- Our Gemfile contains `ruby-next` gem.
- We use [`.rbnextrc`](#CLI-configuration-file) for transpiling options.
If the command fails we warn the end user.
This feature, _auto-transpiling_, is **disabled** by default (will likely be enabled in future versions). You can enable it by calling `RubyNext::Language.setup_gem_load_path(transpile: true)`.
## Runtime usage
It is also possible to transpile Ruby source code in run-time via Ruby Next.
All you need is to `require "ruby-next/language/runtime"` as early as possible to hijack `Kernel#require` and friends.
You can also automatically inject `using RubyNext` to every\* loaded file by also adding `require "ruby-next/core/runtime"`.
Since the runtime mode requires Kernel monkey-patching, it should be used carefully. For example, we use it in Ruby Next tests—works perfectly. But think twice before enabling it in production.
Consider using [Bootsnap](#using-with-bootsnap) integration, 'cause its monkey-patching has been bullet-proofed 😉.
\* Ruby Next doesn't hijack every required file but _watches_ only the configured directories: `./app/`, `./lib/`, `./spec/`, `./test/` (relative to the `pwd`). You can configure the watch dirs:
```ruby
RubyNext::Language.watch_dirs << "path/to/other/dir"
```
### Eval & similar
By default, we do not hijack `Kernel.eval` and similar methods due to some limitations (e.g., there is no easy and efficient way to access the caller's scope, or _binding_, and some evaluations relies on local variables).
If you want to support transpiling in `eval`-like methods, opt-in explicitly by activating the refinement:
```ruby
using RubyNext::Language::Eval
```
## Using with Bootsnap
[Bootsnap][] is a great tool to speed-up your application load and it's included into the default Rails Gemfile. It patches Ruby mechanism of loading source files to make it possible to cache the intermediate representation (_iseq_).
Ruby Next provides a specific integration which allows to add a transpiling step to this process, thus making the transpiler overhead as small as possible, because the cached and **already transpiled** version is used if no changes were made.
To enable this integration, add the following line after the `require "bootsnap/setup"`:
```ruby
require "ruby-next/language/bootsnap"
```
**NOTE:** There is no way to invalidate the cache when you upgrade Ruby Next (e.g., due to the bug fixes), so you should do this manually.
## `uby-next`
_This is [not a typo](https://github.com/ruby-next/ruby-next/pull/8), that’s the way `ruby -ruby-next` works: it’s equal to `ruby -r uby-next`, and [`uby-next.rb`](https://github.com/ruby-next/ruby-next/blob/master/lib/uby-next.rb) is a special file that activates the runtime mode._
You can also enable runtime mode by requiring `uby-next` while running a Ruby executable:
```sh
ruby -ruby-next my_ruby_script.rb
# or
RUBYOPT="-ruby-next" ruby my_ruby_script.rb
# or
ruby -ruby-next -e "puts [2, 4, 5].tally"
```
## Logging and debugging
Ruby Next prints some debugging information when fails to load a file in the runtime mode (and fallbacks to the built-in loading mechanism).
You can disable these warnings either by providing the `RUBY_NEXT_WARN=false` env variable or by setting `RubyNext.silence_warnings = true` in your code.
You can also enable transpiled source code debugging by setting the `RUBY_NEXT_DEBUG=true` env variable. When it's set, Ruby Next prints the transpiled code before loading it.
You can use a file pattern as the value for the env var to limit the output: for example, `RUBY_NEXT_DEBUG=my_script.rb`.
## RuboCop
Since Ruby Next provides support for features not available in RuboCop yet, you need to add a patch for compatibility.
In you `.rubocop.yml` add the following:
```yml
require:
- ruby-next/rubocop
```
You must set `TargetRubyVersion: next` to make RuboCop use a Ruby Next parser.
Alternatively, you can load the patch from the command line by running: `rubocop -r ruby-next/rubocop ...`.
Also, when pre-transpiling source code with `ruby-next nextify`, we suggest ignoring the transpiled files:
```yml
AllCops:
Exclude:
- 'lib/.rbnext/**/*'
```
**NOTE:** you need `ruby-next` gem available in the environment where you run RuboCop (having `ruby-next-core` is not enough).
## Proposed and edge features
Ruby Next aims to bring edge and proposed features to Ruby community before they (hopefully) reach an official Ruby release.
This includes:
- Features already merged to [master](https://github.com/ruby/ruby) (_edge_)
- Features proposed in [Ruby bug tracker](https://bugs.ruby-lang.org/) (_proposed_)
- Features once merged to master but got reverted.
These features are disabled by default, you must opt-in in one of the following ways:
- Add `--edge` or `--proposed` option to `nextify` command when using CLI.
- Enable programmatically when using a runtime mode:
```ruby
# It's important to load language module first
require "ruby-next/language"
require "ruby-next/language/edge"
# or
require "ruby-next/language/proposed"
# and then activate the runtime mode
require "ruby-next/language/runtime"
# or require "ruby-next/language/bootsnap"
```
- Set `RUBY_NEXT_EDGE=1` or `RUBY_NEXT_PROPOSED=1` environment variable.
### Supported edge features
Not yet.
### Supported proposed features
- _Method reference_ operator (`.:`) ([link](https://bugs.ruby-lang.org/issues/13581)).
## Contributing
Bug reports and pull requests are welcome on GitHub at [https://github.com/ruby-next/ruby-next](ttps://github.com/ruby-next/ruby-next).
See also the [development guide](./DEVELOPMENT.md).
## License
The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).
[features]: ./SUPPORTED_FEATURES.md
[features_core]: ./SUPPORTED_FEATURES.md#Core
[features_syntax]: ./SUPPORTED_FEATURES.md#Syntax
[mruby]: https://mruby.org
[JRuby]: https://www.jruby.org
[TruffleRuby]: https://github.com/oracle/truffleruby
[Opal]: https://opalrb.com
[RubyMotion]: http://www.rubymotion.com
[Artichoke]: https://github.com/artichoke/artichoke
[Prism]: https://github.com/prism-rb/prism
[parser]: https://github.com/whitequark/parser
[unparser]: https://github.com/mbj/unparser
[next_parser]: https://github.com/ruby-next/parser
[Bootsnap]: https://github.com/Shopify/bootsnap
[rubocop]: https://github.com/rubocop-hq/rubocop