carve (Ruby)

Native Ruby bindings for the Carve markup language. This gem is a thin native extension built with magnus + rb-sys over the carve-rs engine. The parser is not reimplemented in Ruby; it calls into the Rust crate directly, mirroring how Djot's djotter gem wraps the jotdown crate.

# Gemfile
gem "carve-lang"

bundle install

Or install directly:

gem install carve-lang

Then require "carve" as normal - the gem distribution name is carve-lang but the require path stays carve.

Building from source requires a Rust toolchain (cargo, Rust >= 1.75) and Ruby development headers. RubyGems compiles the native extension at install time via rb_sys.

require "carve"

Carve.to_html("# Hello *world*")
# => "<section id=\"Hello-world\">\n  <h1>Hello <strong>world</strong></h1>\n</section>"

# Carve syntax note: *...* is STRONG (bold), /.../ is EMPHASIS (italic).
Carve.to_html("*bold* and /italic/")

# Enable opt-in extensions (Symbols or Strings, snake_case or hyphenated):
Carve.to_html(<<~CRV, extensions: [:math_block])
  ```math
  a^2 + b^2 = c^2

CRV

Carve.to_html(src, extensions: %w[math-block list-table])

### Recognized extensions

`Carve::EXTENSIONS` is the list, and it comes from the engine rather than from
a copy kept here that could fall behind it:

```ruby
Carve::EXTENSIONS
# => [:autolink, :citations, :"code-callouts", :"code-group", ...]

The canonical names are kebab-case (:"math-block", :"table-of-contents"). Snake_case spellings (:math_block) work as arguments, as do the short aliases this binding has always taken: :math, :permalinks, :mermaid, :dot, :graphviz, :chart, :toc.

An unknown extension name raises ArgumentError.

Carve.parse returns the parsed document as a tree of Ruby Hashes and Arrays, for consumers that want to walk or transform the document rather than render HTML - for example a custom PDF renderer (see carve-hexapdf).

Carve.parse("# Hello *world*")
# => {type: "document", frontmatter: {}, footnote_defs: {},
#     children: [{type: "heading", level: 1,
#                 children: [{type: "text", value: "Hello "},
#                            {type: "emphasis", kind: "strong",
#                             children: [{type: "text", value: "world"}], attrs: nil}],
#                 attrs: nil}],
#     source_len: 15}

Every node is a Hash with a :type key plus its fields; child collections are Arrays; :attrs is nil or a Hash of {id:, classes:, key_values:}. Keys are symbols. This is the raw parse tree (default profile, no extensions), so render-stage extension rewrites are not applied.

By default Carve.to_html renders interactive HTML: client-script constructs (Mermaid/Graphviz/Chart diagrams, math) emit hydration elements (<pre class="mermaid">, ...) and disclosure stays collapsed (<details>).

Pass mode: :static to emit self-contained HTML for print, PDF, or archival. Static mode forces disclosure (<details open>) and pre-renders client-script constructs through the renderers: callables you supply.

Carve.to_html(<<~CRV, extensions: [:fenced_render], mode: :static,
              renderers: { mermaid: ->(src) { "<svg>#{src}</svg>" } })
  ```mermaid
  graph TD; A-->B

CRV

### Renderer callable signatures

The `renderers:` Hash is keyed by Symbol or String (see
`Carve::RENDERER_KEYS`):

| Key | Callable signature | Receives |
| --- | ------------------ | -------- |
| `:mermaid` | `(String) -> String` | the diagram source |
| `:chart` | `(String) -> String` | the chart JSON source |
| `:graphviz` | `(String) -> String` | the DOT / Graphviz source |
| `:math` | `(String, display) -> String` | the TeX source and a `display` boolean (`true` for block / display math, `false` for inline) |

Each callable returns a self-contained HTML string (an `<svg>` / `<img>` for a
diagram, MathML / HTML for math) that the engine emits **verbatim** on the
static path.

### Source fallback (graceful degradation)

When the renderer a construct needs is **absent**, or a supplied renderer
**raises** or returns a **non-String**, the construct degrades to its source -
never blank, and never raw HTML. The fallback source is **HTML-escaped**, so a
construct body containing markup (e.g. `<img onerror=...>`) can never inject raw
HTML. This is part of the cross-implementation graceful-degradation rollout
(spec carve #205; siblings carve-js #242, carve-php #240, carve-rs #143,
carve-py #1).

An unknown `mode:` value or an unknown `renderers:` key raises `ArgumentError`.

## Symbols

A `:name:` symbol renders its literal `:name:` source unless the name is in the
**symbols map** passed as `symbols:` (String or Symbol keys, String values):

```ruby
Carve.to_html("Ship it :rocket: :shrug:", symbols: { "rocket" => "🚀" })
# => "<p>Ship it 🚀 :shrug:</p>"   (an unmapped name stays literal)

The leading word-boundary guard is unaffected by an active map: a:b:c, 10:30: and me@example.com never become symbols. A non-String value raises TypeError.

Security: symbol values are TRUSTED RAW output. A mapped value is inserted into the output unescaped - the same trust class as a renderers: callable. { "b" => "<b>x</b>" } emits a real <b> element, not escaped text. This is deliberate (processor configuration is trusted). Never build a symbols map out of untrusted / user-supplied input.

A top-level heading is wrapped, along with the content following it up to the next same-or-shallower heading, in a <section> carrying the heading's id (spec PART 9 §13). Only the id moves - {#install .featured} gives <section id="install"><h2 class="featured"> - and a heading inside a blockquote, div or list item is not wrapped at all.

Pass sections: false to render headings flat, with the id back on the <h*>:

Carve.to_html("# A\n\np\n")
# => "<section id=\"A\">\n  <h1>A</h1>\n  <p>p</p>\n</section>"

Carve.to_html("# A\n\np\n", sections: false)
# => "<h1 id=\"A\">A</h1>\n<p>p</p>"

This is for a host whose CSS or JS assumes rendered blocks are direct children of the content container - the .stack > * + * spacing idiom, :first-child, nth-child() counting, DOM child walks - all of which stop matching once a wrapper sits in between. It is the one output change that breaks a document whose source migrated cleanly.

Nothing else changes: ids, collision dedup, </#id> cross-references, implicit [Heading][] references and heading numbering all resolve against the slug rather than the element carrying it. The endnotes <section role="doc-endnotes"> is a separate construct and is still emitted.

Carve's normative hardening is always on and needs no option: dangerous URL schemes are blanked, event-handler attributes like onclick are dropped, and the bidi override/isolate characters behind Trojan Source are removed from rendered text.

Raw passthrough is the deliberate exception. A ```=html block or a `…`{=html} span renders verbatim by design, so it is the one thing input you did not author has to switch off:

Carve.to_html(user_input, safe: true, profile: :comment)

safe: escapes those raw blocks and spans instead of emitting them. profile: restricts which constructs are allowed at all and caps input length - :full, :article, :comment or :minimal, String or Symbol. An unknown name raises ArgumentError rather than being ignored.

A profile rejection raises too, rather than returning something that looks like output:

Carve.to_html("x" * 20_000, profile: :minimal)
# ArgumentError: Profile violations: 'document' is not allowed: max_length_exceeded (...)

That matters for untrusted input: the engine's infallible entry point answers a rejection with an empty String, which a caller cannot tell from a document that legitimately rendered to nothing.

Full recipe, defaults and threat model: Security.

carve fmt --stamp (in any Carve engine) records the spec version a document was last processed under. This gem reads that marker back, so a repository of stored .crv files can be checked for documents predating a breaking spec change:

Carve.read_stamp(source)
# => {version: "0.1", generated_by: "carve-php 0.1.0"}

Carve.needs_review?(source)   # true when the document predates this engine

An unstamped document answers true: its provenance is unknown, and assuming it is current is the unsafe direction. Both marker forms are read, and a marker written by any engine reads the same - the format is the contract, not any one API - so the answer matches carve-php, carve-js, carve-rs and carve-go on the same document.

What a version difference means is the versioning contract: only [behavior] changelog entries between the stamped version and yours can require a document change.

bundle install
rake compile   # builds the Rust extension into lib/carve/carve.so
rake test      # runs the minitest suite

export BINDGEN_EXTRA_CLANG_ARGS="-I/usr/lib/gcc/x86_64-linux-gnu/13/include"

ext/carve/Cargo.toml pins a specific carve-rs commit for reproducible gem builds:

carve_rs = { package = "carve-lang", git = "https://github.com/markup-carve/carve-rs", rev = "..." }

Read the current revision out of ext/carve/Cargo.toml rather than from a copy here. This section used to quote one, and it drifted three bumps behind the manifest before anyone noticed - a duplicated value goes stale the first time someone edits the original, and a stale one here is worse than none because it reads as authoritative.

The crate is imported under the alias carve_rs. It is published as carve-lang (carve-rs renamed it from carve), so a pin at any revision past that rename needs package = "carve-lang" as above.

When bumping the rev, run rake compile and commit the resulting ext/carve/Cargo.lock in the same change. The lock records the resolved revision, so leaving it behind means every fresh clone gets a dirty working tree on its first build and the gem can resolve to a different engine than the one that was tested.

Whether the pin is current is not a judgment call: CI runs the mandatory spec corpus through the compiled extension and requires byte-identical HTML, so a pin that has fallen behind fails a build. Locally:

CARVE_SPEC_CORPUS=/path/to/carve/tests/corpus bundle exec rake test

MIT, markup-carve.