☯️ Markdown::Merge

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Markdown::Merge provides intelligent Markdown file merging using tree_haver backends. It can be used standalone or through parser-specific wrappers.

Direct usage (with auto-detected or specified backend):

require "markdown/merge"

# Auto-detect available backend (commonmarker or markly)
merger = Markdown::Merge::SmartMerger.new(template_content, dest_content)
result = merger.merge

# Or specify a backend explicitly
merger = Markdown::Merge::SmartMerger.new(template_content, dest_content, backend: :markly)

Via parser-specific wrappers (for hard dependencies and backend-specific defaults):

• commonmarker-merge - Uses Comrak (Rust) via Commonmarker
• markly-merge - Uses libcmark-gfm (C) via Markly

• Multiple Backends: Supports Commonmarker and Markly through tree_haver's unified API
• Type Normalization: Canonical node types (:heading, :paragraph, etc.) work across all backends
• Extensible: Register custom backends via NodeTypeNormalizer.register_backend
• Structure-Aware: Understands headings, paragraphs, lists, code blocks, tables, and other block elements
• Freeze Block Support: Respects freeze markers (default: markdown-merge:freeze / markdown-merge:unfreeze) for template merge control - customizable to match your project's conventions
• Inner-Merge Code Blocks: Optionally merge fenced code blocks using language-specific mergers (Ruby → prism-merge, YAML → psych-merge, JSON → json-merge, TOML → toml-merge)
• Table Match Refiner: Fuzzy matching algorithm for tables with similar but not identical headers
• Full Provenance: Tracks origin of every node
• Customizable:
  • backend - select :commonmarker, :markly, or :auto
  • signature_generator - callable custom signature generators
  • preference - setting of :template, :destination, or a Hash for per-node-type preferences
  • add_template_only_nodes - setting to retain sections that do not exist in destination
  • freeze_token - customize freeze block markers (default: "markdown-merge")
  • inner_merge_code_blocks - enable language-aware code block merging
  • match_refiner - fuzzy matching for unmatched nodes (e.g., TableMatchRefiner)

Signatures computed by default for common Markdown block elements:

The *-merge gem family provides intelligent, AST-based merging for various file formats. At the foundation is tree_haver, which provides a unified cross-Ruby parsing API that works seamlessly across MRI, JRuby, and TruffleRuby.

Gem	Version	CI		Language / Format	Parser Backend(s)	Description
tree_haver			Multi	Supported Backends: MRI C, Rust, FFI, Java, Prism, Psych, Commonmarker, Markly, Citrus, Parslet	Foundation: Cross-Ruby adapter for parsing libraries (like Faraday for HTTP)
ast-merge			Text	internal	Infrastructure: Shared base classes and merge logic for all *-merge gems
bash-merge			Bash	tree-sitter-bash (via tree_haver)	Smart merge for Bash scripts
commonmarker-merge			Markdown	Commonmarker (via tree_haver)	Smart merge for Markdown (CommonMark via comrak Rust)
dotenv-merge			Dotenv	internal	Smart merge for .env files
json-merge			JSON	tree-sitter-json (via tree_haver)	Smart merge for JSON files
jsonc-merge			JSONC	tree-sitter-jsonc (via tree_haver)	⚠️ Proof of concept; Smart merge for JSON with Comments
markdown-merge			Markdown	Commonmarker / Markly (via tree_haver)	Foundation: Shared base for Markdown mergers with inner code block merging
markly-merge			Markdown	Markly (via tree_haver)	Smart merge for Markdown (CommonMark via cmark-gfm C)
prism-merge			Ruby	Prism (prism std lib gem)	Smart merge for Ruby source files
psych-merge			YAML	Psych (psych std lib gem)	Smart merge for YAML files
rbs-merge			RBS	tree-sitter-bash (via tree_haver), RBS (rbs std lib gem)	Smart merge for Ruby type signatures
toml-merge			TOML	Parslet + toml, Citrus + toml-rb, tree-sitter-toml (all via tree_haver)	Smart merge for TOML files

tree_haver supports multiple parsing backends, but not all backends work on all Ruby platforms:

Legend: ✅ = Works, ❌ = Does not work, ❓ = Untested

Why some backends don't work on certain platforms:

• JRuby: Runs on the JVM; cannot load native C/Rust extensions (.so files)
• TruffleRuby: Has C API emulation via Sulong/LLVM, but it doesn't expose all MRI internals that native extensions require (e.g., RBasic.flags, rb_gc_writebarrier)
• FFI on TruffleRuby: TruffleRuby's FFI implementation doesn't support returning structs by value, which tree-sitter's C API requires

Example implementations for the gem templating use case:

Tokens to Remember
Works with JRuby
Works with Truffle Ruby
Works with MRI Ruby 3
Support & Community
Source
Documentation
Compliance
Style
Maintainer 🎖️
... 💖	🧊 🐙 🛖 🧪

Compatible with MRI Ruby 3.2.0+, and concordant releases of JRuby, and TruffleRuby.

Federated DVCS Repository	Status	Issues	PRs	Wiki	CI	Discussions
🧪 kettle-rb/markdown-merge on GitLab	The Truth	💚	💚	💚	🐭 Tiny Matrix	➖
🧊 kettle-rb/markdown-merge on CodeBerg	An Ethical Mirror (Donate)	💚	💚	➖	⭕️ No Matrix	➖
🐙 kettle-rb/markdown-merge on GitHub	Another Mirror	💚	💚	💚	💯 Full Matrix	💚
🎮️ Discord Server		Let's	talk	about	this	library!

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

bundle add markdown-merge

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

gem install markdown-merge

This gem is cryptographically signed, and has verifiable SHA-256 and SHA-512 checksums by 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:

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:

gem install markdown-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:

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.

The SmartMerger class is the main entry point for merging Markdown files:

require "markdown/merge"

merger = Markdown::Merge::SmartMerger.new(
  template_content,
  dest_content,

  # Backend selection (default: :auto)
  # :auto - auto-detect available backend (tries commonmarker first, then markly)
  # :commonmarker - use Commonmarker (comrak Rust parser)
  # :markly - use Markly (cmark-gfm C library)
  backend: :auto,

  # Which version to prefer when nodes match but differ
  # :destination (default) - keep destination content (preserves customizations)
  # :template - use template content (applies updates)
  preference: :destination,

  # Whether to add template-only nodes to the result
  # false (default) - only include sections that exist in destination
  # true - include all template sections
  add_template_only_nodes: false,

  # Token for freeze block markers
  # Default: "markdown-merge"
  # Looks for: <!-- markdown-merge:freeze --> / <!-- markdown-merge:unfreeze -->
  freeze_token: "markdown-merge",

  # Enable inner-merge for fenced code blocks
  # false (default) - use standard conflict resolution for code blocks
  # true - merge code block contents using language-specific mergers
  # CodeBlockMerger instance - use custom CodeBlockMerger
  inner_merge_code_blocks: false,

  # Match refiner for fuzzy matching of unmatched nodes
  # nil (default) - exact matching only
  # TableMatchRefiner.new - enable fuzzy table matching
  match_refiner: nil,

  # Custom signature generator (optional)
  # Receives a node (wrapped with canonical merge_type), returns a signature array or nil
  # Return the node itself to fall through to default signature
  signature_generator: nil,

  # Backend-specific options (passed through to parser)
  # For commonmarker: options: {}
  # For markly: flags: Markly::DEFAULT, extensions: [:table]
)

Important: When matching nodes by text content (such as for anchor patterns in PartialTemplateMerger), the .text method returns plain text without markdown formatting.

This means:

• Markdown: ### The `*-merge` Gem Family
• .text returns: "The *-merge Gem Family\n"

The backticks around *-merge are stripped because they are inline formatting, not content. This is true for both Commonmarker and Markly backends.

Anchor pattern examples:

# ❌ WRONG - backticks are stripped, so this won't match
anchor: { type: :heading, text: /`\*-merge` Gem Family/ }

# ✅ CORRECT - match the plain text content
anchor: { type: :heading, text: /\*-merge.*Gem Family/ }

# ✅ CORRECT - use beginning anchor for exact heading match
anchor: { type: :heading, text: /^The \*-merge Gem Family/ }

Other markdown formatting that is stripped from .text:

• Bold: **text** → text
• Italic: *text* or _text_ → text
• Code: `code` → code
• Links: [text](url) → text
• Images: ![alt](src) → alt

Note: Different parsers may have other idiosyncrasies. For example:

• Trailing newlines may or may not be present
• Whitespace normalization may differ
• Entity encoding may vary

Always test your patterns against actual parsed content when building merge recipes.

markdown-merge normalizes node types across backends so merge rules are portable:

# These are equivalent regardless of backend
# Markly's :header becomes :heading
# Markly's :hrule becomes :thematic_break
# etc.

# Register a custom backend's type mappings
Markdown::Merge::NodeTypeNormalizer.register_backend(:my_parser, {
  h1: :heading,
  h2: :heading,
  para: :paragraph,
  # ...
})

For convenience, parser-specific wrappers provide backend-specific defaults:

# commonmarker-merge (freeze_token: "commonmarker-merge", inner_merge_code_blocks: false)
require "commonmarker/merge"
merger = Commonmarker::Merge::SmartMerger.new(template, dest, options: {})

# markly-merge (freeze_token: "markly-merge", inner_merge_code_blocks: true)
require "markly/merge"
merger = Markly::Merge::SmartMerger.new(template, dest, flags: Markly::DEFAULT, extensions: [:table])

### Freeze Blocks

Freeze blocks protect sections from being modified during merges. They are marked
with HTML comments that are invisible when the Markdown is rendered:

```markdown
<!-- markdown-merge:freeze -->
## This Section Is Protected

Any content here will be preserved exactly as-is during merges.
The merge tool will not modify, replace, or remove this content.

<!-- markdown-merge:unfreeze -->

Add an optional frozen reason to document why:

<!-- markdown-merge:freeze Custom table - manually maintained -->
| Feature | Status |
|---------|--------|
| Custom  | ✅     |
<!-- markdown-merge:unfreeze -->

When enabled, fenced code blocks are merged using language-specific *-merge gems:

merger = SomeParser::Merge::SmartMerger.new(
  template,
  destination,
  inner_merge_code_blocks: true,
)

Supported languages and their mergers:

Example with a Ruby code block:

```ruby
# Template
class MyClass
  def new_method
    puts "from template"
  end
end)))))))))))
```

When merged(with:

```ruby
# Destination
class MyClass
  def existing_method
    puts "custom"
  end
end)
```

Result (with inner_merge_code_blocks: true):

```ruby
class MyClass
  def existing_method
    puts "custom"
  end

  def new_method
    puts "from template"
  end
end
```

When tables don't match by exact signature, the TableMatchRefiner uses fuzzy matching to pair tables with similar structure:

refiner = Markdown::Merge::TableMatchRefiner.new(
  threshold: 0.5,  # Minimum similarity (0.0-1.0)
  algorithm_options: {
    weights: {
      header_match: 0.25,  # Header cell similarity
      first_column: 0.20,  # Row label similarity
      row_content: 0.25,   # Row content overlap
      total_cells: 0.15,   # Overall cell matching
      position: 0.15,      # Position distance
    },
  },
)

merger = SomeParser::Merge::SmartMerger.new(
  template,
  destination,
  match_refiner: refiner,
)

Enable debug logging to see merge decisions:

export MARKDOWN_MERGE_DEBUG=1

Note: This gem provides base classes for implementers. End users should use commonmarker-merge or markly-merge instead.

Use a parser-specific implementation:

# Option 1: Using commonmarker-merge (Comrak/Rust)
require "commonmarker/merge"

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

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

File.write("merged.md", result.content)

# Option 2: Using markly-merge (libcmark-gfm/C)
require "markly/merge"

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

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

File.write("merged.md", result.to_markdown)

Creating a new parser-specific implementation:

require "markdown/merge"

module MyParser
  module Merge
    class FileAnalysis < Markdown::Merge::FileAnalysisBase
      def parse_document(source)
        # Parse source and return root document node
        MyParser.parse(source)
      end

      def next_sibling(node)
        # Return the next sibling of a node
        node.next_sibling
      end

      def compute_parser_signature(node)
        # Compute signature for parser-specific nodes
        # Or call super for default implementation
        super
      end
    end

    class SmartMerger < Markdown::Merge::SmartMergerBase
      def create_file_analysis(content, **options)
        FileAnalysis.new(content, **options)
      end

      def node_to_source(node, analysis)
        case node
        when Markdown::Merge::FreezeNode
          node.full_text
        else
          # Convert node back to source text
          node.to_markdown
        end
      end
    end
  end
end

Both implementations support freeze blocks for protecting customized sections:

# My Project

## Installation

<!-- markdown-merge:freeze Custom install instructions -->
This installation section has been customized and will be preserved
during template merges, regardless of what the template contains.
<!-- markdown-merge:unfreeze -->

## Usage

Standard usage section - can be updated from template.

Content between freeze markers is always preserved from the destination file, even when the template has different content for that section.

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.

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

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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

See SECURITY.md.

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.

See CONTRIBUTING.md.

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

Made with contributors-img.

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

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("markdown-merge", "~> 1.0")

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"

See CHANGELOG.md for a list of releases.

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

• Copyright (c) 2025 Peter H. Boling, of Galtzo.com , and markdown-merge contributors.

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.

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Thanks for RTFM. ☺️