Asciidoctor Extensions Lab

This repository is a lab for experimenting with Ruby-based Asciidoctor extensions using the Extensions API. Please do not use this code in production. The code is untested. It is also not packaged and distributed. The purpose of these examples is to demonstrate how extensions are set up, how to write them, and what they can do. The examples also offer patterns that can be reused when implementing your own extension.

In order to use the extensions in this repository, you need to clone the repository. Then, you need to pass the location of the extension you want to use to Asciidoctor using the -r CLI option or require it in your Ruby script if you are using the Asciidoctor API.

If you only want to test the extensions in this repository, skip ahead to Using an extension.

If you want to use one of the extensions from this lab in production, and perhaps develop it further, please import it into a new project and distribute it as a RubyGem. If you’re prepared to maintain it for the community, you can submit a request in the project chat to graduate it a top-level project in the Asciidoctor organization. When writing your own extension, we recommend that you study the extensions section in the Asciidoctor documentation.

Extension types
Extension files
Extension catalog
Using an extension
Adding an extension
Other extensions
Copyright

Extension types

We have the following types of extensions in the lab:

Preprocessor - processes the AsciiDoc source before it is parsed
IncludeProcessor - intercepts the AsciiDoc include directive
TreeProcessor - processes the AsciiDoc document (AST) after block-level parsing is complete
Postprocessor - processes the converted output before it is written to the output stream (or disk)
DocinfoProcessor - contributes additional content to the header or footer of the output document
BlockProcessor - adds a custom delimited block
BlockMacroProcessor - adds a custom block macro
InlineMacroProcessor - adds a custom inline macro

The type of extension (e.g, -block-macro) is always used in the name of the extension registration file and directory to make it easy to distinguish. You can also look for examples using git grep. For example, to look for a BlockMacroProcessor, run the following command:

$ git grep BlockMacroProcessor lib/

You’ll get a result like this:

lib/gist-block-macro/extension.rb:class GistBlockMacro < Extensions::BlockMacroProcessor
lib/pass-block-macro/extension.rb:class PassBlockMacro < Extensions::BlockMacroProcessor
lib/tree-block-macro/extension.rb:class TreeBlockMacro < Asciidoctor::Extensions::BlockMacroProcessor

Extension files

Each extension consists of several files:

A file that registers the extension (sometimes also contains the extension)
A file with the extension itself (when not defined in the registration file)
A file with sample AsciiDoc source to use to test the extension
Auxiliary assets needed by the extension

For example, the emoji-inline-macro extension has four files:

lib/emoji-inline-macro.rb (registration file)
lib/emoji-inline-macro/extension.rb (extension file)
lib/emoji-inline-macro/sample.adoc (sample AsciiDoc file)
lib/emoji-inline-macro/twemoji-awesome.css (auxiliary asset file)

📎	The registration file (e.g., emoji-inline-macro.rb) goes in the lib directory whereas the remaining files go inside a directory whose base name matches the name of the registration file (e.g., emoji-inline-macro).

Extension catalog

The following extensions are available in the lab. When the registration of the extension is in a separate file from the extension code, you require the registration file.

AutoXrefTreeprocessor (registration & extension code): Refers images, tables, listings, sections by their numbers.
BackToTopDocinfoProcessor (registration & extension code): Adds a floating back to top button to the bottom right corner of the page.
~~ChartBlockMacro~~: Adds a chart block and block macro to AsciiDoc powered by c3js, chartist or chartjs. Replaced by Asciidoctor Chart.
ChromeInlineMacro (registration, extension code): Adds an inline macro for linking to a chrome:// URI.
CopyToClipboardDocinfoProcessor (registration, extension code): Adds a source toolbox with a copy to clipboard button to all source blocks.
CopyrightFooterPostprocessor (registration, extension code): Adds a copyright to the document footer based on the value of the copyright attribute.
CustomAdmonitionBlock (registration, extension code): Introduces a new admonition block type, complete with a custom icon.
DocstatInlineMacro (registration, extension code): A macro that displays the word count and estimated reading time of the current document.
DumpAttributesBlockMacro (registration & extension code): Dumps the document attributes as attribute entries in a source block.
EmojiInlineMacro (registration, extension code): Adds an emoji inline macro for inserting emoji by name.
EnableSourcemapPreprocessor (registration & extension code): Specifies sourcemap attribute for document.
ExternalHeaderAttributesPreprocessor (registration, extension code): Reads additional AsciiDoc attributes from a YAML-based configuration file and adds them to the document header.
FoldLinesTreeProcessor (registration & extension code): Replaces newlines (i.e., line feeds) in paragraphs with a single space.
FootnotesBlockMacro (registration, extension code): Consumes the footnotes from the document catalog and puts them into a dedicated section.
FrontMatterPreprocessor (registration, extension code): Emulates the built-in behavior of Asciidoctor to sweep away YAML front matter into the front-matter attribute.
GitMetadataInlineMacro (registration, extension code): Provide information on references using a macro (e.g. commits, branches and tags).
GitMetadataPreprocessor (registration, extension code): Provide information on the local git repository, e.g. the branch or tag name or the commit id.
GistBlockMacro (registration, extension code): Adds a block macro to embed a gist into an AsciiDoc document.
GlobIncludeProcessor (registration, extension code): Enhances the include directive to support a glob expression to include all matching files.
GoogleAnalyticsDocinfoProcessor (registration & extension code): Adds the Google Analytics code for the account identified by the google-analytics-account attribute to the bottom of the HTML document.
HardbreaksPreprocessor (registration & extension code): Adds hardbreaks to the end of all non-empty lines that aren’t section titles.
HighlightTreeprocessor (registration & extension code): Highlights source blocks using the highlight command.
ImplicitApidocInlineMacro (registration & extension code): Adds an inline macro for linking to the Javadoc of a class in the Java EE API.
ImplicitHeaderIncludeProcessor (registration, extension code): Skips the implicit author line below the document title in included documents.
LicenseUrlDocinfoProcessor (registration & extension code): Adds a link to the license specified by the license attribute to the document header.
LoremBlockMacro (registration & extension code): Generates lorem ipsum text using the Middleman lorem extension. (Requires middleman >= 4.0.0).
ManInlineMacro (registration, extension code): Adds an inline macro for linking to another man page (used in the Git documentation).
~~MathematicalTreeprocessor~~: Converts all latexmath blocks to SVG using the Mathematical library. Replaced by Asciidoctor Mathematical.
MarkdownLinkInlineMacro (registration & extension code): Parses a Markdown-style link.
MentionsInlineMacro (registration & extension code): Detects Twitter-style username mentions and converts them to links.
MultipageHtml5Converter (registration & extension code): A converter that chunks the HTML5 output into multiple pages. This extension is merely a proof of concept. You can find a complete implementation of a multipage HTML converter at https://github.com/owenh000/asciidoctor-multipage.
MultirowTableHeaderTreeProcessor (registration & extension code): Promotes additional rows from the table body to the table head(er). Number of header rows is controlled by the hrows attribute on the table block.
NestedOpenBlock (registration & extension code): Allows open blocks to be nested by repurposing the example container as an open block.
NumberParagraphsTreeProcessor (registration, extension code): Naively numbers paragraphs based on position.
PassBlockMacro (registration, extension code): Adds a pass block macro to AsciiDoc.
PickInlineMacro (registration & extension code): Adds an inline macro for selecting between two values based on the value of another attribute.
PullquoteInlineMacro (registration, extension code): Adds an inline macro to pull a quote out of the flow and display it in a sidebar.
RubyAttributesPreprocessor (registration, extension code): Makes information about the Ruby runtime available to the document by defining document attributes for all constants that begin with RUBY_ (e.g, ruby-version).
SectnumoffsetTreeprocessor (registration & extension code): Increments all level-1 section numbers (and subsequently all subsections) by the value of the sectnumoffset attribute.
ShellSessionTreeProcessor (registration, extension code): Detects a shell command and trailing output and styles it for display in HTML.
ShoutBlock (registration, extension code): Converts all text inside a delimited block named shout to uppercase and adds trailing exclamation marks.
ShowCommentsPreprocessor (registration & extension code): Converts line comments to visual elements (normally dropped).
SlimBlock (registration, extension code): Passes the content in blocks named slim to the Slim template engine for processing.
StepsPostprocessor (registration, extension code): Styles an ordered list as a procedure list.
TelInlineMacro (registration & extension code): Adds an inline macro for linking to a tel: URI.
TermInlineMacro (registration & extension code): Demonstrates how to convert an inline macro into a span of text with a role.
TexPreprocessor (registration, extension code): Interprets tex markup embedded inside of AsciiDoc.
TextqlBlock (registration & extension code): Adds a block for using textql to process data in an AsciiDoc document.
TreeBlockMacro (registration, extension code): Adds a block macro to show the output of the tree command.
UndoReplacementsPostprocessor (registration & extension code): Reverses the text replacements that are performed by Asciidoctor.
UriIncludeProcessor (registration, extension code): Emulates the built-in behavior of Asciidoctor to include content from a URI.
ViewResultDocinfoProcessor (registration, extension code): Adds an interactive toggle to block content marked as a view result.
WhitespaceIncludeProcessor (registration & extension code): An include processor that substitutes tabs with spaces (naively) in included source code.
XmlEntityPostprocessor (registration, extension code): Converts named entities to character entities so they can be resolved without the use of external entity declarations.

Using an extension

Before creating your own extensions, it would be wise to run one yourself. First, make sure Asciidoctor is installed:

$ gem install asciidoctor

Next, run the extension from the root directory of the project:

$ asciidoctor -r lib/emoji-inline-macro.rb lib/emoji-inline-macro/sample.adoc
# asciidoctor: FAILED: 'lib/emoji-inline-macro.rb' could not be loaded
# Use --trace for backtrace

Oops! We forgot to include the leading ./ when using the -r flag Let’s try again:

$ asciidoctor -r ./lib/emoji-inline-macro.rb lib/emoji-inline-macro/sample.adoc

All right, it ran! The output file, sample.html, was created in the same directory as the source file, sample.adoc.

The relevant bits of the input and output are shown below.

lib/emoji-inline-macro/sample.adoc

Faster than a emoji:turtle[1x]!

This is an example of how you can emoji:heart[lg] Asciidoctor and Twitter Emoji.

lib/emoji-inline-macro/sample.html

<div class="paragraph">
<p>Faster than a <i class="twa twa-1x twa-turtle"></i>!</p>
</div>
<div class="paragraph">
<p>This is an example of how you can <i class="twa twa-lg twa-heart"></i> Asciidoctor and Twitter Emoji.</p>
</div>

⚠️	Certain extensions require additional libraries. Please consult the extension’s registration file for details about what is required to use it.

Adding an extension

You can find examples of various ways to define an extension in the lib/shout-block.rb extension.

Shorthand (DSL)

If you’re creating a trivial extension, you can define the extension using the extension DSL directly in the registration file. Create a new file in the lib directory. Include the extension type in the name of the file so others are clear what type of extension it is.

lib/sample-block.rb

Asciidoctor::Extensions.register do
  block do
    named :sample
    on_context :open

    process do |parent, reader, attrs|
      create_paragraph parent, reader.lines, attrs
    end
  end
end

Formal

If you’re creating a more complex extension or want to enable reuse, you’re encouraged to move the extension code to the extension.rb inside a directory with the same base name as the registration file. In the case of a block, block macro or inline macro, this enables you to register the extension multiple times.

lib/sample-block.rb

RUBY_ENGINE == 'opal' ? (require 'sample-block/extension') : (require_relative 'sample-block/extension')

Asciidoctor::Extensions.register do
  block SampleBlock
end

lib/sample-block/extension.rb

class SampleBlock < Asciidoctor::Extensions::BlockProcessor
  use_dsl
  named :sample
  on_context :open

  def process parent, reader, attrs
    create_paragraph parent, reader.lines, attrs
  end
end

It’s customary to provide a sample AsciiDoc file named sample.adoc inside the extension subdirectory that others can use to try the extension. You should also add your extension to the Extension catalog section along with a short description of what it does.

Other extensions

See this list of official and community extensions for Asciidoctor.

Here are some other experimental extensions.

imagemap block processor - Adds an image with an imagemap using targets specified in the contents of the block. Note that this extension does not follow the standard use of block attrlists and is therefore considered to be experimental. However, it could be a useful starting point for someone interesting in creating one that is more conventional.

You may also be interested in these extensions which were submitted, but never merged:

Copyright

See the LICENSE file for details.

asciidoctor / asciidoctor-extensions-lab