📍 NOTE
RubyGems (the GitHub org, not the website) suffered a hostile takeover in September 2025.
Ultimately 4 maintainers were hard removed and a reason has been given for only 1 of those, while 2 others resigned in protest.
It is a complicated story which is difficult to parse quickly.
Simply put - there was active policy for adding or removing maintainers/owners of rubygems and bundler, and those policies were not followed.
I'm adding notes like this to gems because I don't condone theft of repositories or gems from their rightful owners.
If a similar theft happened with my repos/gems, I'd hope some would stand up for me.
Disenfranchised former-maintainers have started gem.coop.
Once available I will publish there exclusively; unless RubyCentral makes amends with the community.
The "Technology for Humans: Joel Draper" podcast episode by reinteractive is the most cogent summary I'm aware of.
See here, here and here for more info on what comes next.
What I'm doing: A (WIP) proposal for bundler/gem scopes, and a (WIP) proposal for a federated gem server.

☯️ Prism::Merge

if ci_badges.map(&:color).detect { it != "green"} ☝️ let me know, as I may have missed the discord notification.

if ci_badges.map(&:color).all? { it == "green"} 👇️ send money so I can do more of this. FLOSS maintenance is now my full-time job.

🌻 Synopsis

Prism::Merge is a standalone Ruby module that intelligently merges two versions of a Ruby file using Prism AST analysis. It's like a smart "git merge" specifically designed for Ruby code. I wrote this to aid in my comprehensive gem templating tool kettle-dev.

Key Features

AST-Aware: Uses Prism parser to understand Ruby structure
Intelligent: Matches nodes by structural signatures
Comment-Preserving: Comments are properly attached to relevant nodes and/or placement
Freeze Block Support: Respects kettle-dev:freeze markers for template merge control
Full Provenance: Tracks origin of every line
Customizable: Supports custom signature generators
Standalone: No dependencies other than prism

Example

require "prism/merge"

template = File.read("template.rb")
destination = File.read("destination.rb")

merger = Prism::Merge::SmartMerger.new(template, destination)
result = merger.merge

File.write("merged.rb", result)

💡 Info you can shake a stick at

Tokens to Remember
Works with JRuby
Works with Truffle Ruby
Works with MRI Ruby 3
Works with MRI Ruby 2	![Ruby 2.7 Compat][💎ruby-2.7i]
Support & Community
Source
Documentation
Compliance
Style
Maintainer 🎖️
`...` 💖	🧊 🐙 🛖 🧪

Compatibility

Compatible with MRI Ruby 2.7.0+, and concordant releases of JRuby, and TruffleRuby.

🚚 Amazing test matrix was brought to you by	🔎 appraisal2 🔎 and the color 💚 green 💚
👟 Check it out!	✨ github.com/appraisal-rb/appraisal2 ✨

Federated DVCS

Find this repo on federated forges (Coming soon!)

| Federated [DVCS][💎d-in-dvcs] Repository | Status | Issues | PRs | Wiki | CI | Discussions | |-------------------------------------------------|-----------------------------------------------------------------------|---------------------------|--------------------------|---------------------------|--------------------------|------------------------------| | 🧪 [kettle-rb/prism-merge on GitLab][📜src-gl] | The Truth | [💚][🤝gl-issues] | [💚][🤝gl-pulls] | [💚][📜gl-wiki] | 🐭 Tiny Matrix | ➖ | | 🧊 [kettle-rb/prism-merge on CodeBerg][📜src-cb] | An Ethical Mirror ([Donate][🤝cb-donate]) | [💚][🤝cb-issues] | [💚][🤝cb-pulls] | ➖ | ⭕️ No Matrix | ➖ | | 🐙 [kettle-rb/prism-merge on GitHub][📜src-gh] | Another Mirror | [💚][🤝gh-issues] | [💚][🤝gh-pulls] | [💚][📜gh-wiki] | 💯 Full Matrix | [💚][gh-discussions] | | 🎮️ [Discord Server][✉️discord-invite] | [![Live Chat on Discord][✉️discord-invite-img-ftb]][✉️discord-invite] | [Let's][✉️discord-invite] | [talk][✉️discord-invite] | [about][✉️discord-invite] | [this][✉️discord-invite] | [library!][✉️discord-invite] |

Enterprise Support

Available as part of the Tidelift Subscription.

Need enterprise-level guarantees?

The maintainers of this and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source packages you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact packages you use. [![Get help from me on Tidelift][🏙️entsup-tidelift-img]][🏙️entsup-tidelift] - 💡Subscribe for support guarantees covering _all_ your FLOSS dependencies - 💡Tidelift is part of [Sonar][🏙️entsup-tidelift-sonar] - 💡Tidelift pays maintainers to maintain the software you depend on!
📊`@`Pointy Haired Boss: An [enterprise support][🏙️entsup-tidelift] subscription is "[never gonna let you down][🧮kloc]", and *supports* open source maintainers Alternatively: - [![Live Chat on Discord][✉️discord-invite-img-ftb]][✉️discord-invite] - [![Get help from me on Upwork][👨🏼‍🏫expsup-upwork-img]][👨🏼‍🏫expsup-upwork] - [![Get help from me on Codementor][👨🏼‍🏫expsup-codementor-img]][👨🏼‍🏫expsup-codementor]

✨ Installation

Install the gem and add to the application's Gemfile by executing:

bundle add prism-merge

If bundler is not being used to manage dependencies, install the gem by executing:

gem install prism-merge

🔒 Secure Installation

For Medium or High Security Installations

This gem is cryptographically signed, and has verifiable [SHA-256 and SHA-512][💎SHA_checksums] checksums by [stone_checksums][💎stone_checksums]. Be sure the gem you install hasn’t been tampered with by following the instructions below. Add my public key (if you haven’t already, expires 2045-04-29) as a trusted certificate: ```console gem cert --add <(curl -Ls https://raw.github.com/galtzo-floss/certs/main/pboling.pem) ``` You only need to do that once. Then proceed to install with: ```console gem install prism-merge -P HighSecurity ``` The `HighSecurity` trust profile will verify signed gems, and not allow the installation of unsigned dependencies. If you want to up your security game full-time: ```console bundle config set --global trust-policy MediumSecurity ``` `MediumSecurity` instead of `HighSecurity` is necessary if not all the gems you use are signed. NOTE: Be prepared to track down certs for signed gems and add them the same way you added mine.

⚙️ Configuration

Prism::Merge works out of the box with zero configuration, but offers customization options for advanced use cases.

Signature Match Preference

Control which version to use when nodes have matching signatures but different content:

# Use template version (for version files, configs where template has updates)
merger = Prism::Merge::SmartMerger.new(
  template,
  destination,
  signature_match_preference: :template,
)

# Use destination version (for Appraisals, configs with customizations)
merger = Prism::Merge::SmartMerger.new(
  template,
  destination,
  signature_match_preference: :destination,  # This is the default
)

When to use each:

:template - Template contains canonical/updated values
- Version files (VERSION = "2.0.0" should replace VERSION = "1.0.0")
- Configuration updates (API_ENDPOINT should be updated)
- Conditional bodies (if ENV["DEBUG"] should use template's implementation)
:destination (default) - Destination contains customizations
- Appraisals files (destination has project-specific gem versions)
- Project-specific configurations
- Custom implementations

Template-Only Nodes

Control whether to add nodes that only exist in the template:

# Add template-only nodes (for merging new features/constants)
merger = Prism::Merge::SmartMerger.new(
  template,
  destination,
  add_template_only_nodes: true,
)

# Skip template-only nodes (for templates with placeholder content)
merger = Prism::Merge::SmartMerger.new(
  template,
  destination,
  add_template_only_nodes: false,  # This is the default
)

When to use each:

true - Template has new content to add
- New constants (NAME = "myapp" should be added to destination)
- New methods/classes from template
- Required configuration options
false (default) - Template has placeholder/example content
- Appraisals templates with ruby version blocks not in destination
- Example configurations that shouldn't be added
- Template-only nodes would create unwanted additions

Combined Configuration

For different merge scenarios:

# Scenario 1: Version file merge (template wins, add new constants)
merger = Prism::Merge::SmartMerger.new(
  template_content,
  dest_content,
  signature_match_preference: :template,
  add_template_only_nodes: true,
)
# Result: VERSION updated to template value, NAME constant added

# Scenario 2: Appraisals merge (destination wins, skip template-only blocks)
merger = Prism::Merge::SmartMerger.new(
  template_content,
  dest_content,
  signature_match_preference: :destination,  # default
  add_template_only_nodes: false,             # default
)
# Result: Destination gem versions preserved, template-only ruby blocks skipped

# Scenario 3: Config merge (mix and match)
merger = Prism::Merge::SmartMerger.new(
  template_content,
  dest_content,
  signature_match_preference: :destination,  # Keep custom values
  add_template_only_nodes: true,              # But add new required configs
)
# Result: Existing configs keep destination values, new configs added from template

Custom Signature Generator

By default, Prism::Merge uses intelligent structural signatures to match nodes:

Conditionals (if/unless) are matched by their condition only
Assignments (constants, variables) are matched by their name only
Method calls are matched by name and arguments (not block body)
Other nodes are matched by class and full source code

You can provide a custom signature generator to control matching behavior:

signature_generator = lambda do |node|
  case node
  when Prism::CallNode
    # Match method calls by name only, ignoring arguments
    [:call, node.name]
  when Prism::DefNode
    # Match method definitions by name and parameters
    [:def, node.name, node.parameters&.slice]
  when Prism::ClassNode
    # Match classes by name
    [:class, node.constant_path.slice]
  else
    # Default matching
    [node.class.name.split("::").last.to_sym, node.slice]
  end
end

merger = Prism::Merge::SmartMerger.new(
  template_content,
  destination_content,
  signature_generator: signature_generator,
  signature_match_preference: :template,
  add_template_only_nodes: true,
)

Freeze Blocks

Protect sections in the destination file from being overwritten by the template using freeze markers:

# In your destination.rb file
# kettle-dev:freeze
gem "custom-gem", path: "../custom"
# Add any custom configuration you want to preserve
# kettle-dev:unfreeze

Freeze blocks are always preserved from the destination file during merge, regardless of template content.

Integration with Existing Systems

If you're integrating with an existing system that has its own signature logic:

# Use your existing signature function
my_signature_func = ->(node) { MySystem.calculate_signature(node) }

merger = Prism::Merge::SmartMerger.new(
  template,
  destination,
  signature_generator: my_signature_func,
)

🔧 Basic Usage

Simple Merge

The most basic usage merges two Ruby files:

require "prism/merge"

template = File.read("template.rb")
destination = File.read("destination.rb")

merger = Prism::Merge::SmartMerger.new(template, destination)
result = merger.merge

File.write("merged.rb", result)

Understanding the Merge

Prism::Merge intelligently combines files by:

Finding Anchors: Identifies matching sections between files
Detecting Boundaries: Locates areas where files differ
Resolving Conflicts: Uses structural signatures to merge differences
Preserving Context: Maintains comments and freeze blocks

Example:

# template.rb
VERSION = "2.0.0"

def greet(name)
  puts "Hello, #{name}!"
end

# destination.rb
VERSION = "1.0.0"

def greet(name)
  puts "Hello, #{name}!"
end

def custom_method
  # This is destination-only
end

# After merge:
# - VERSION from template (2.0.0) replaces destination (1.0.0)
# - greet method matches, template version kept
# - custom_method is preserved (destination-only)

With Debug Information

Get detailed information about merge decisions:

merger = Prism::Merge::SmartMerger.new(template, destination)
debug_result = merger.merge_with_debug

puts debug_result[:content]      # Final merged content
puts debug_result[:statistics]   # Decision counts
puts debug_result[:debug]        # Line-by-line provenance

The debug output shows:

debug_result[:statistics]
# => {
#   kept_template: 42,        # Lines from template (no conflict)
#   kept_destination: 8,      # Lines from destination (no conflict)
#   replaced: 5,              # Template replaced matching destination
#   appended: 3,              # Destination-only content added
#   freeze_block: 2           # Lines from freeze blocks
# }

Error Handling

Prism::Merge raises exceptions when files have syntax errors:

begin
  merger = Prism::Merge::SmartMerger.new(template, destination)
  result = merger.merge
rescue Prism::Merge::TemplateParseError => e
  puts "Template has syntax errors"
  puts "Content: #{e.content}"
  puts "Parse errors: #{e.parse_result.errors}"
rescue Prism::Merge::DestinationParseError => e
  puts "Destination has syntax errors"
  puts "Content: #{e.content}"
  puts "Parse errors: #{e.parse_result.errors}"
end

Validating Before Merge

Check if files are valid before attempting a merge:

template_analysis = Prism::Merge::FileAnalysis.new(template_content)
dest_analysis = Prism::Merge::FileAnalysis.new(dest_content)

if template_analysis.valid? && dest_analysis.valid?
  merger = Prism::Merge::SmartMerger.new(template_content, dest_content)
  result = merger.merge
else
  puts "Files have syntax errors" unless template_analysis.valid?
  puts "Cannot merge"
end

Working with Freeze Blocks

Protect custom sections from template updates:

# destination.rb
class MyApp
  # kettle-dev:freeze
  CUSTOM_CONFIG = {
    api_key: ENV.fetch("API_KEY"),
    endpoint: "https://custom.example.com",
  }
  # kettle-dev:unfreeze

  VERSION = "1.0.0"
end

# template.rb
class MyApp
  CUSTOM_CONFIG = {}  # Template wants to reset this

  VERSION = "2.0.0"
end

# After merge, CUSTOM_CONFIG keeps destination values
# but VERSION is updated to 2.0.0

Advanced: Inspect Merge Components

For debugging or understanding the merge process:

# Analyze files separately
template_analysis = Prism::Merge::FileAnalysis.new(template)
dest_analysis = Prism::Merge::FileAnalysis.new(destination)

puts "Template statements: #{template_analysis.statements.length}"
puts "Template freeze blocks: #{template_analysis.freeze_blocks.length}"

# See what anchors and boundaries are found
aligner = Prism::Merge::FileAligner.new(template_analysis, dest_analysis)
boundaries = aligner.align

puts "Anchors (matching sections): #{aligner.anchors.length}"
aligner.anchors.each do |anchor|
  puts "  Lines #{anchor.template_start}-#{anchor.template_end} match"
end

puts "Boundaries (differences): #{boundaries.length}"
boundaries.each do |boundary|
  puts "  Template #{boundary.template_range} vs Dest #{boundary.dest_range}"
end

Integration Example

Use Prism::Merge in your own templating system:

class MyTemplateEngine
  def merge_ruby_file(template_path, destination_path)
    template = File.read(template_path)
    destination = File.exist?(destination_path) ? File.read(destination_path) : ""

    merger = Prism::Merge::SmartMerger.new(template, destination)
    merged_content = merger.merge

    File.write(destination_path, merged_content)

    # Return statistics for reporting
    debug_result = merger.merge_with_debug
    debug_result[:statistics]
  rescue Prism::Merge::Error => e
    puts "Merge failed: #{e.message}"
    # Fall back to template only
    File.write(destination_path, template)
    nil
  end
end

Testing Your Merges

Example RSpec test:

require "prism/merge"

RSpec.describe("Ruby file merging") do
  it "updates VERSION from template" do
    template = "      VERSION = \"2.0.0\"\n      def hello; end\n    RUBY\n\n    destination = <<~RUBY\n      VERSION = \"1.0.0\"\n      def hello; end\n      def custom; end\n    RUBY\n\n    merger = Prism::Merge::SmartMerger.new(template, destination)\n    result = merger.merge\n\n    # Template version wins\n    expect(result).to(include('VERSION = \"2.0.0\"'))\n    # Destination-only method preserved\n    expect(result).to(include(\"def custom\"))\n  end\n\n  it \"preserves freeze blocks\" do\n    template = <<~RUBY\n      CONFIG = {}\n    RUBY\n\n    destination = <<~RUBY\n      # kettle-dev:freeze\n      CONFIG = { key: \"secret\" }\n      # kettle-dev:unfreeze\n    RUBY\n\n    merger = Prism::Merge::SmartMerger.new(template, destination)\n    result = merger.merge\n\n    # Freeze block content preserved\n    expect(result).to(include('CONFIG = { key: \"secret\" }'))\n  end\nend\n"

🦷 FLOSS Funding

While kettle-rb tools are free software and will always be, the project would benefit immensely from some funding. Raising a monthly budget of... "dollars" would make the project more sustainable.

We welcome both individual and corporate sponsors! We also offer a wide array of funding channels to account for your preferences (although currently Open Collective is our preferred funding platform).

If you're working in a company that's making significant use of kettle-rb tools we'd appreciate it if you suggest to your company to become a kettle-rb sponsor.

You can support the development of kettle-rb tools via GitHub Sponsors, Liberapay, PayPal, Open Collective and Tidelift.

📍 NOTE
If doing a sponsorship in the form of donation is problematic for your company from an accounting standpoint, we'd recommend the use of Tidelift, where you can get a support-like subscription instead.

Open Collective for Individuals

Support us with a monthly donation and help us continue our activities. [Become a backer]

NOTE: kettle-readme-backers updates this list every day, automatically.

No backers yet. Be the first!

Open Collective for Organizations

Become a sponsor and get your logo on our README on GitHub with a link to your site. [Become a sponsor]

NOTE: kettle-readme-backers updates this list every day, automatically.

No sponsors yet. Be the first!

Another way to support open-source

I’m driven by a passion to foster a thriving open-source community – a space where people can tackle complex problems, no matter how small. Revitalizing libraries that have fallen into disrepair, and building new libraries focused on solving real-world challenges, are my passions. I was recently affected by layoffs, and the tech jobs market is unwelcoming. I’m reaching out here because your support would significantly aid my efforts to provide for my family, and my farm (11 🐔 chickens, 2 🐶 dogs, 3 🐰 rabbits, 8 🐈‍ cats).

If you work at a company that uses my work, please encourage them to support me as a corporate sponsor. My work on gems you use might show up in bundle fund.

I’m developing a new library, floss_funding, designed to empower open-source developers like myself to get paid for the work we do, in a sustainable way. Please give it a look.

Floss-Funding.dev: 👉️ No network calls. 👉️ No tracking. 👉️ No oversight. 👉️ Minimal crypto hashing. 💡 Easily disabled nags

🔐 Security

See SECURITY.md.

🤝 Contributing

If you need some ideas of where to help, you could work on adding more code coverage, or if it is already 💯 (see below) check reek, issues, or PRs, or use the gem and think about how it could be better.

We so if you make changes, remember to update it.

See CONTRIBUTING.md for more detailed instructions.

🚀 Release Instructions

See CONTRIBUTING.md.

Code Coverage

🪇 Code of Conduct

Everyone interacting with this project's codebases, issue trackers, chat rooms and mailing lists agrees to follow the .

🌈 Contributors

Made with contributors-img.

Also see GitLab Contributors: https://gitlab.com/kettle-rb/prism-merge/-/graphs/main

⭐️ Star History

📌 Versioning

This Library adheres to . Violations of this scheme should be reported as bugs. Specifically, if a minor or patch version is released that breaks backward compatibility, a new version should be immediately released that restores compatibility. Breaking changes to the public API will only be introduced with new major versions.

dropping support for a platform is both obviously and objectively a breaking change
—Jordan Harband (@ljharb, maintainer of SemVer) in SemVer issue 716

I understand that policy doesn't work universally ("exceptions to every rule!"), but it is the policy here. As such, in many cases it is good to specify a dependency on this library using the Pessimistic Version Constraint with two digits of precision.

For example:

spec.add_dependency("prism-merge", "~> 1.0")

📌 Is "Platform Support" part of the public API? More details inside.

SemVer should, IMO, but doesn't explicitly, say that dropping support for specific Platforms is a *breaking change* to an API, and for that reason the bike shedding is endless. To get a better understanding of how SemVer is intended to work over a project's lifetime, read this article from the creator of SemVer: - ["Major Version Numbers are Not Sacred"][📌major-versions-not-sacred]

See CHANGELOG.md for a list of releases.

📄 License

The gem is available as open source under the terms of the MIT License . See LICENSE.txt for the official Copyright Notice.

© Copyright

🤑 A request for help

Maintainers have teeth and need to pay their dentists. After getting laid off in an RIF in March, and encountering difficulty finding a new one, I began spending most of my time building open source tools. I'm hoping to be able to pay for my kids' health insurance this month, so if you value the work I am doing, I need your support. Please consider sponsoring me or the project.

To join the community or get help 👇️ Join the Discord.

To say "thanks!" ☝️ Join the Discord or 👇️ send money.

💌 💌 💌

Please give the project a star ⭐ ♥.

Thanks for RTFM. ☺️