[Awesome Ruby Gem - Abstract Syntax Tree (AST)] Use unparser gem to produce equivalent source code from Parser's ASTs

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parser

unparser generate equivalent source for ASTs from parser. You can also use unparser to produce equivalent source code from Parser’s ASTs whitequark/parser: A Ruby parser. - https://github.com/whitequark/parser.

Installation

You can install it as a gem:

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$ gem install unparser

or add it into a Gemfile (Bundler):

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# Gemfile

# mbj/unparser: Turn Ruby AST into semantically equivalent Ruby source
# https://github.com/mbj/unparser](https://github.com/mbj/unparser
gem 'unparser', '0.6.0'

Then, run bundle install.

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$ bundle install

Usage

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require 'parser/current'
require 'unparser'

ast = Unparser.parse('your(ruby(code))')

Unparser.unparse(ast) # => 'your(ruby(code))'

To preserve the comments from the source:

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require 'parser/current'
require 'unparser'

ast, comments = Unparser.parse_with_comments('your(ruby(code)) # with comments')

Unparser.unparse(ast, comments) # => 'your(ruby(code)) # with comments'

Passing in manually constructed AST:

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require 'parser/current'
require 'unparser'

module YourHelper
  def s(type, *children)
    Parser::AST::Node.new(type, children)
  end
end

include YourHelper

node = s(:def,
  :foo,
  s(:args,
    s(:arg, :x)
  ),
  s(:send,
    s(:lvar, :x),
    :+,
    s(:int, 3)
  )
)

Unparser.unparse(node) # => "def foo(x)\n  x + 3\nend"

Note: DO NOT attempt to pass in nodes generated via AST::Sexp#s, these ones return API incompatible AST::Node instances, unparser needs Parser::AST::Node instances.

Equivalent vs identical:

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require 'unparser'

node = Unparser.parse(<<~'RUBY')
  %w[foo bar]
RUBY

generated = Unparser.unparse(node) # ["foo", "bar"], NOT %w[foo bar] !

code == generated                 # false, not identical code
Unparser.parse(generated) == node # true, but identical AST

Summary: unparser does not reproduce your source! It produces equivalent source.

References

[1] mbj/unparser: Turn Ruby AST into semantically equivalent Ruby source - https://github.com/mbj/unparser

[2] unparser | RubyGems.org | your community gem host - https://rubygems.org/gems/unparser

[3] whitequark/parser: A Ruby parser. - https://github.com/whitequark/parser