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.

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 if you would like us to support older Ruby versions.

Using only polyfills

First, install a gem:

# 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:

require "ruby-next"

And activate the refinement in every file where you want to use it*:

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 a predictable behaviour. That's why we recommend using refinements for gems development.

Alternatively, you can go with monkey-patches. Just add this line:

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.

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 below).

Installation:

# Gemfile
gem "ruby-next"

# gemspec
spec.add_dependency "ruby-next"

# or install globally
gem install ruby-next

The list of supported syntax features.

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). Thus, the transpiled code being identical in terms of functionality has a 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

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:

$ 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

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:

$ 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:

$ 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

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:

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:

$ ruby-next core_ext -l --name=filter --name=deconstruct
2.6 extensions:
  - ArrayFilter
  - EnumerableFilter
  - HashFilter

2.7 extensions:
  - ArrayDeconstruct
  - EnumerableFilterMap
  - EnumeratorLazyFilterMap
  - HashDeconstructKeys
  - StructDeconstruct

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):

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 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).

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 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:

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:

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":

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`

You can also enable runtime mode by requiring uby-next while running a Ruby executable:

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:

require:
  - ruby-next/rubocop

NOTE: You should use TargetRubyVersion: 2.7.

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:

AllCops:
  Exclude:
    - 'lib/.rbnext/**/*'

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 (edge)
Features proposed in Ruby bug tracker (proposed)
Features once merged to master but got reverted.

These features require a custom parser.

Currently, the only such feature is the method reference operator:

Add --enable-method-reference option to nextify command when using CLI.
OR add it programmatically when using a runtime mode (see example).
OR set RUBY_NEXT_ENABLE_METHOD_REFERENCE=1 environment variable (works with CLI as well).

Prerequisites

Our own version of parser gem is hosted on Github Package Registry. That makes the installation process a bit more complicated than usual.

You must obtain an access token to use it. See the GPR docs.

Installing with Bundler

First, configure your bundler to access GPR:

bundle config --local https://rubygems.pkg.github.com/ruby-next USERNAME:ACCESS_TOKEN

Then, add to your Gemfile:

source "https://rubygems.pkg.github.com/ruby-next" do
  gem "parser", "~> 2.7.0.100", "< 2.7.1"
end

gem "ruby-next"

NOTE: we don't add parser and unparser to the gem's runtime deps, 'cause they're not necessary if you only need polyfills.

Installing globally via `gem`

You can install ruby-next globally by running the following commands:

gem install parser -v "~> 2.7.0.100" -v "< 2.7.1" --source "https://USERNAME:ACCESS_TOKEN@rubygems.pkg.github.com/ruby-next"
gem install ruby-next

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ruby-next/ruby-next.

License

The gem is available as open source under the terms of the MIT License.

X1ting/ruby-next

Ruby Next

Links

Table of contents

Overview

Using only polyfills

Transpiling

Transpiler modes

CLI

`ruby-next nextify`

`ruby-next core_ext`

Integrating into a gem development

Runtime usage

Eval & similar

Using with Bootsnap

`uby-next`

Logging and debugging

RuboCop

Proposed and edge features

Prerequisites

Installing with Bundler

Installing globally via `gem`

Contributing

License

X1ting/ruby-next

Ruby Next

Links

Table of contents

Overview

Using only polyfills

Transpiling

Transpiler modes

CLI

ruby-next nextify

ruby-next core_ext

Integrating into a gem development

Runtime usage

Eval & similar

Using with Bootsnap

uby-next

Logging and debugging

RuboCop

Proposed and edge features

Prerequisites

Installing with Bundler

Installing globally via gem

Contributing

License

`ruby-next nextify`

`ruby-next core_ext`

`uby-next`

Installing globally via `gem`