https://github.com/mbj/unparser

Turn Ruby AST into semantically equivalent Ruby source
https://github.com/mbj/unparser

Keywords

parser ruby ruby-syntax unparser

Keywords from Contributors

rubocop activerecord static-code-analysis code-formatter activejob mvc rubygems rspec rack feature-flag

Last synced: about 24 hours ago
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Repository metadata

Turn Ruby AST into semantically equivalent Ruby source

Host: GitHub
URL: https://github.com/mbj/unparser
Owner: mbj
License: mit
Created: 2013-04-08T09:54:20.000Z (almost 13 years ago)
Default Branch: main
Last Pushed: 2026-01-06T01:04:24.000Z (about 2 months ago)
Last Synced: 2026-02-20T06:56:44.858Z (11 days ago)
Topics: parser, ruby, ruby-syntax, unparser
Language: Ruby
Homepage:
Size: 1.28 MB
Stars: 326
Watchers: 9
Forks: 50
Open Issues: 6
Releases: 0
Metadata Files:
- Readme: README.md
- Changelog: Changelog.md
- License: LICENSE

unparser

Generate equivalent source for ASTs from parser.

The following constraints apply:

No support for macruby extensions
Only support for the modern AST format
Only support for Ruby >= 3.2

Notable Users:

mutant - Code review engine via mutation testing.
ruby-next - Ruby Syntax Backports.
Many other reverse-dependencies.

(if you want your tool to be mentioned here please PR the addition with a TLDR of your use case).

Public API:

While unparser is in the 0.x versions its public API can change any moment.
I recommend to use ~> 0.x.y style version constraints that should give the best mileage.

Usage

require 'parser/current'
require 'unparser'

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

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

To preserve the comments from the source:

require 'parser/current'
require 'unparser'

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

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

Passing in manually constructed AST:

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:

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.

Ruby Versions:

Unparsers primay reason for existance is mutant and its
supported Ruby-Versions.

Basically: All non EOL MRI releases.

If you need to generate Ruby Syntax outside of this band feel free to contact me (email in gemspec).

Testing:

Unparser currently successfully round trips almost all ruby code around. Using Ruby >= 2.6.
If there is a non round trippable example that is NOT subjected to known Limitations.
please report a bug.

On CI unparser is currently tested against rubyspec with minor excludes.

Limitations:

Source parsed with magic encoding headers other than UTF-8 and that have literal strings.
where parts can be represented in UTF-8 will fail to get reproduced.

A fix is possible as with latest updates the parser gem carries the information.

Example:

Original-Source:

# -*- encoding: binary -*-

"\x98\x76\xAB\xCD\x45\x32\xEF\x01\x01\x23\x45\x67\x89\xAB\xCD\xEF"

Original-AST:

(str "\x98v\xAB\xCDE2\xEF\x01\x01#Eg\x89\xAB\xCD\xEF")

Generated-Source:

"\x98v\xAB\xCDE2\xEF\x01\x01#Eg\x89\xAB\xCD\xEF"

Generated-AST:

(str "\x98v\xAB\xCDE2\xEF\u0001\u0001#Eg\x89\xAB\xCD\xEF")

Diff:

@@ -1,2 +1,2 @@
-(str "\x98v\xAB\xCDE2\xEF\x01\x01#Eg\x89\xAB\xCD\xEF")
+(str "\x98v\xAB\xCDE2\xEF\u0001\u0001#Eg\x89\xAB\xCD\xEF")

Installation

Install the gem unparser via your prefered method.

People

Various people contributed to this repository. See Contributors.

Included Libraries

For dependency reduction reasons unparser ships vendored (and reduced) versions of:

abstract_type -> Unparser::AbstractType
adamantium -> Unparser::Adamantium
anima -> Unparser::Anima
concord -> Unparser::Concord
memoizable -> Unparser::Adamantium
mprelude -> Unparser::Either

Contributing

Fork the project.
Make your feature addition or bug fix.
Add tests for it. This is important so I don't break it in a
future version unintentionally.
Commit, do not mess with version
(if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
Send me a pull request. Bonus points for topic branches.

Known Users

RailsRocket - A no-code app builder that creates Rails apps

License

See LICENSE file.

Owner metadata

Name: Markus Schirp
Login: mbj
Email: mbj@schirp-dso.com
Kind: user
Description: Master of Disaster.
Website:
Location: /dev/urandom
Twitter: _m_b_j_
Company: /proc/self
Icon url: https://avatars.githubusercontent.com/u/117966?u=4f362766f68e589ac0c3c8f799d23e90169668b8&v=4
Repositories: 163
Last ynced at: 2025-10-29T04:59:34.125Z
Profile URL: https://github.com/mbj

GitHub Events

Total

Delete event: 14
Pull request event: 64
Fork event: 4
Issues event: 11
Watch event: 8
Issue comment event: 73
Push event: 62
Pull request review comment event: 14
Pull request review event: 31
Create event: 20

Last Year

Delete event: 9
Pull request event: 55
Fork event: 3
Issues event: 9
Watch event: 5
Issue comment event: 64
Push event: 52
Pull request review event: 30
Pull request review comment event: 13
Create event: 16

Committers metadata

Last synced: 8 days ago

Total Commits: 988
Total Committers: 30
Avg Commits per committer: 32.933
Development Distribution Score (DDS): 0.149

Commits in past year: 42
Committers in past year: 4
Avg Commits per committer in past year: 10.5
Development Distribution Score (DDS) in past year: 0.452

Name	Email	Commits
Markus Schirp	m**j@s**m	841
dependabot[bot]	4****]	44
viralpraxis	i**k@g**m	23
Trent Ogren	t**2@g**m	21
Vsevolod Romashov	7@7****u	11
Erik Berlin	s**k@g**m	10
Daniel Gollahon	d**n@g**m	5
Matijs van Zuijlen	m**s@m**t	4
Bartek Bułat	b**t@g**m	3
Dan Kubb	d**b@g**m	3
Nathan Wenneker	n**n@p**m	2
Sergei Prikhodko	p****a	2
Vladimir Dementyev	d**m@g**m	2
Filipp Pirozhkov	f**v@t**m	1
Adam Hess	a**1@g**m	1
Alan Wu	X****r	1
Alex Dowad	a**g@g**m	1
Guillaume Malette	g**e@s**m	1
Ivo Wever	i**r@g**m	1
John Backus	j**s@g**m	1
Olle Jonsson	o**n@g**m	1
Piotr Solnica	p**a@g**m	1
Piotr Szotkowski	c**l@c**t	1
Rodrigo Andrés Vilina	r**a@g**m	1
Russell Davis	r**l@s**m	1
Stan Hu	s**u@g**m	1
Vidar Hokstad	v**r@h**m	1
paulodeon	m**l@p**m	1
sanemat	o**n@g**m	1
vzvu3k6k	v****k	1

Committer domains:

Issue and Pull Request metadata

Last synced: 7 days ago

Total issues: 24
Total pull requests: 192
Average time to close issues: about 1 year
Average time to close pull requests: 10 days
Total issue authors: 16
Total pull request authors: 10
Average comments per issue: 5.5
Average comments per pull request: 0.61
Merged pull request: 119
Bot issues: 0
Bot pull requests: 67

Past year issues: 2
Past year pull requests: 60
Past year average time to close issues: 2 months
Past year average time to close pull requests: 4 days
Past year issue authors: 2
Past year pull request authors: 5
Past year average comments per issue: 16.0
Past year average comments per pull request: 0.78
Past year merged pull request: 50
Past year bot issues: 0
Past year bot pull requests: 2

More stats: https://issues.ecosyste.ms/repositories/lookup?url=https://github.com/mbj/unparser

Top Issue Authors

akimd (4)
dgollahon (3)
boutil (2)
marcandre (2)
prikha (2)
camertron (1)
csabahenk (1)
belene (1)
backus (1)
petekinnecom (1)
vidarh (1)
neil-ongkingco-apollo (1)
viralpraxis (1)
pilipenok (1)
mbj (1)

Top Pull Request Authors

mbj (67)
dependabot[bot] (67)
viralpraxis (43)
prikha (7)
dgollahon (3)
paulodeon (1)
camertron (1)
vidarh (1)
sferik (1)
vaporyhumo (1)

Top Issue Labels

bug (5)

Top Pull Request Labels

dependencies (67)
bug (2)
ruby (2)

Package metadata

Total packages: 10
Total downloads:
- rubygems: 189,097,120 total
Total docker downloads: 872,427,828
Total dependent packages: 82 (may contain duplicates)
Total dependent repositories: 4,254 (may contain duplicates)
Total versions: 237
Total maintainers: 3

gem.coop: unparser

Generate equivalent source for parser gem AST nodes

Homepage: http://github.com/mbj/unparser
Documentation: http://www.rubydoc.info/gems/unparser/
Licenses: MIT
Latest release: 0.8.2 (published 7 days ago)
Last Synced: 2026-02-24T15:45:33.253Z (7 days ago)
Versions: 80
Dependent Packages: 0
Dependent Repositories: 0
Downloads: 94,548,560 Total
Docker Downloads: 436,213,914
Rankings:
- Dependent repos count: 0.0%
- Dependent packages count: 0.0%
- Average: 0.137%
- Downloads: 0.271%
- Docker downloads count: 0.275%
Maintainers (3)
- mbjs
- dkubb
- snusnu
Funding:
- https://github.com/sponsors/mbj

rubygems.org: unparser