Jekyll_plugin_support is a Ruby gem that provides a framework for writing and testing Jekyll plugins.

Jekyll_plugin_support can be used to create simple Jekyll plugins in the _plugins/ directory of your Jekyll project, or gem-based Jekyll plugins.

At present, only Jekyll tags and blocks are supported.

Plugins that use jekyll_plugin_support include:

• jekyll_all_collections
• jekyll_badge
• jekyll_emoji
• jekyll_flexible_include
• jekyll_href
• jekyll_img
• jekyll_plugin_template
• jekyll_outline
• jekyll_pre
• jekyll_quote

... and also the demonstration plugins in jekyll_plugin_support

Jekyll plugin tags created from jekyll_plugin_support framework automatically have the following features:

1. Boilerplate is removed, so you can focus on the required logic and output.
2. Arguments are parsed for keywords and name/value parameters.
3. Single or double quotes can be used for arguments and parameters.
4. Important variables are defined.
5. Error handling is standardized, and includes an automatically defined error type and corresponding CSS tag for each Jekyll tag.
6. Liquid variables can be passed as parameters to tags, and used in the body of block tags.
7. Registration is automatic, and important configuration details are reported during registration.
8. A custom logger is created for each tag, independent of the default Jekyll logger.
9. Variables can be defined in _config.yml, and optionally have different values for debug mode, production mode and test mode.
10. An attribution message is available.
11. Draft pages are automatically detected.

In addition, a demonstration website is provided for easy testing of your plugins.

Jekyll_plugin_support is packaged as a Ruby gem. If your project is a custom plugin that will reside in a Jekyll project’s _plugins directory, add the following line to your Jekyll plugin’s Gemfile.

group :jekyll_plugins do
  # ...
  gem 'jekyll_plugin_support', '>= 0.8.0'
  # ...
end

Otherwise, if your custom plugin will be packaged into a gem, add the following to your plugin’s .gemspec:

Gem::Specification.new do |spec|
  # ...
  spec.add_dependency 'jekyll_plugin_support', '>= 0.8.0'
  # ...
end

Install the jekyll_plugin_support Ruby gem and mark it as a dependency of your project by typing:

$ bundle

Copy the CSS classes from demo/assets/css/jekyll_plugin_support.css to your Jekyll project’s CSS file.

JekyllSupport::JekyllBlock and JekyllSupport::JekyllTag provide support for Jekyll tag block plugins and Jekyll inline tag plugins, respectively. They are very similar in construction and usage.

Instead of subclassing your custom Jekyll block tag class from Liquid::Block, subclass from JekyllSupport::JekyllBlock. Similarly, instead of subclassing your custom Jekyll tag class from Liquid::Tag, subclass from JekyllSupport::JekyllTag.

Both JekyllSupport classes instantiate new instances of PluginMetaLogger (called @logger) and JekyllPluginHelper (called @helper).

JekyllPluginHelper defines a generic initialize method, and your tag or block tag class should not need to override it. Also, your tag or block tag class should not define a method called render, because jekyll_plugin_support defines one.

Instead, define a method called render_impl. For inline tags, render_impl does not accept any parameters. For block tags, a single parameter is required, which contains text passed from your block in the page.

Your implementation of render_impl can parse parameters passed to the tag / block tag, as described in Tag Parameter Parsing.

Please see the demo/ project for a well-documented set of demonstration Jekyll plugins that are built from jekyll_plugin_support. Additional information is available here and the jekyll_plugin_support documentation.

JekyllSupport::JekyllBlock and JekyllSupport::JekyllTag provide support for Jekyll block tags and Jekyll inline tags, respectively. They are similar in construction and usage.

Instead of subclassing your Jekyll block tag class from Liquid::Block, subclass from JekyllSupport::JekyllBlock instead.

Likewise, instead of subclassing your Jekyll inline tag class from Liquid::Tag, subclass from JekyllSupport::JekyllTag instead.

Both JekyllSupport classes instantiate new instances of PluginMetaLogger (called @logger) and JekyllPluginHelper (called @helper).

Both JekyllSupport classes define a generic initialize method, and your inline tag or block tag class should not override it.

Also, your inline tag or block tag class should not define a method called render, because both JekyllSupport classes define this method.

Instead, define a method called render_impl. For inline tags, render_impl does not accept any parameters. For block tags, a single parameter is required, which contains any text enclosed within your block.

Jekyll_plugin_support defines the following Ruby variables that you can use in your plugin’s render_impl method:

• @argument_string Unparsed markup passed as a parameter to your block tag and inline tag.

• @attribution Attribution markup

• @config YAML Jekyll site configuration file

• @helper JekyllPluginHelper instance for your plugin.

• @layout Layout information

• @logger jekyll_plugin_logger instance for your Jekyll plugin.

• @mode Indicates production, test or development mode.

• @page Page variables

• @paginator Pagination variables

• @scopes See the jekyll_plugin_support demo project

• @site Site variables

• @tag_config Contents of the section of _config.yml named after your plugin.

• @tag_name Name of your Jekyll block tag or inline tag plugin.

• @theme Theme variables

• text Content provided to your block tag.

Tag arguments can be obtained within render_impl. Both keyword options and name/value parameters are supported.

Both JekyllTag and JekyllBlock use the standard Ruby mechanism for parsing command-line options: shellwords and key_value_parser.

All your code has to do is to specify the keywords to search for in the string passed from the HTML page that your tag is embedded in. The included demo website has examples; both demo/_plugins/demo_inline_tag.rb and demo/_plugins/demo_block_tag.rb contain the following:

@keyword1  = @helper.parameter_specified? 'keyword1'
@keyword2  = @helper.parameter_specified? 'keyword2'
@name1     = @helper.parameter_specified? 'name1'
@name2     = @helper.parameter_specified? 'name2'

If an argument has a variable reference in it, the value of the variable is substituted for the reference. For example, given:

• _layouts/default.html defines a variable called var_layout in its front matter.
• index.html defines a variable called var_page in its front matter.
• index.html assigns a variable called x via the liquid assign statement.

... then the following references in a page will be substituted for their values in arguments and in block tag bodies:

{% my_block_tag
  param1="x={{x}}"
  param2="var_page={{page.var_page}}"
  param3="var_layout={{layout.var_layout}}"
%}

Assigned variables do not need a namespace: x={{x}}

Page variables must be qualified with the 'page' namespace:
  var_page={{page.var_page}}

Layout variables must be qualified with the 'layout' namespace:
  var_layout={{layout.var_layout}}
{% endmy_block_tag %}

You can see similar code in demo/demo_inline_tag.html.

The page['excerpt'] and page['output'] key/value pairs are removed from processing because of recursion issues. You cannot look up those values from a jekyll_plugin_support plugin.

For all keyword options, values specified in the document may be provided. If a value is not provided, the value true is assumed. Otherwise, if a value is provided, it must be wrapped in single or double quotes.

The following examples use the die_if_error keyword option for the pre and exec tags from the jekyll_pre plugin %}.

The following sets die_if_error true:

{% pre die_if_error %} ... {% endpre %}

The above is the same as writing:

{% pre die_if_error='true' %} ... {% endpre %}

Or writing:

{% pre die_if_error="true" %} ... {% endpre %}

Neglecting to provide surrounding quotes around the provided value causes the parser to not recognize the option. Instead, what you had intended to be the keyword/value pair will be parsed as part of the command. For the pre tag, this means the erroneous string becomes part of the label value, unless label is explicitly specified. For the exec tag, this means the erroneous string becomes part of the command to execute. The following demonstrates the error.

{% pre die_if_error=false %} ... {% endpre %}

The above causes the label to be die_if_error=false.

{% exec die_if_error=false ls %} ... {% endpre %}

The above causes the command to be executed to be die_if_error=false ls instead of ls.

Parameter values can be quoted.

If the value consists of only one token then quoting is optional. The following name/value parameters all have the same result:

• pay_tuesday="true"
• pay_tuesday='true'
• pay_tuesday=true
• pay_tuesday

If the values consist of more than one token, quotes must be used. The following examples both yield the same result:

• pay_tuesday="maybe not"
• pay_tuesday='maybe not'

After your plugin has parsed all the keyword options and name/value parameters, call @helper.remaining_markup to obtain the remaining markup that was passed to your plugin.

jekyll_plugin_support provides support for Liquid variables to be defined in _config.yml, in a section called liquid-vars. These variables behave exactly like Liquid variables defined by assign and capture expressions, except they are global in scope; these variables are available in every Jekyll web page.

The following _config.yml fragment defines 3 variables called var1, var2 and var3:

liquid-vars:
  var1: value1
  var2: 'value 2'
  var3: value3

Liquid variables defined in this manner are intended to be embedded in a webpage. They are can be used like any other Liquid variable.

Jekyll expands Liquid variable references during the page rendering process. Jekyll does not expand Liquid variable references passes as parameters to tag and block plugins, however. However, plugins made from jekyll_plugin_support automatically expand all types of variable references passed as parameters and in block tag bodies.

Jekyll_plugin_support tag and block plugins expand the following types of variables:

• Jekyll_plugin_support configuration variables, discussed above.
• Jekyll page and layout variables.
• Inline Liquid variables (defined in assign and capture statements).

In the following example web page, Jekyll expands the var1 reference within the <p></p> tag, but not the var1 or var2 references passed to my_plugin.

<p>This is the value of var1: {{var1}}.</p>

{% my_plugin param1="{{var1}}" param2="{{var2}}" %}

Assuming that my_plugin was written as a jekyll_plugin_support plugin, all variable references in its parameters are expanded. Thus, the above is interpreted as follows when my_plugin is evaluated during the Jekyll rendering process:

<p>This is the value of var1: value1.</p>

{% my_plugin param1="value1" param2="value 2" %}

Jekyll_plugin_support expands most of the plugin variables described above, replacing Liquid variable references with their values. The exception is @argument_string, which is not expanded.

jekyll_plugin_support allows Liquid variables defined in _config.yml to have different values when Jekyll is running in development, production and test modes. When injecting variables into your Jekyll website, Jekyll_plugin_support refers to definitions specific to the current environment, and then refers to other definitions that are not overridden.

Here is an example:

liquid-vars:
  development:
    var1: 'http://localhost:4444/demo_block_tag.html'
    var2: 'http://localhost:4444/demo_inline_tag.html'
  production:
    var1: 'https://github.com/django/django/blob/3.1.7'
    var2: 'https://github.com/django-oscar/django-oscar/blob/3.0.2'
  var3: 'https://github.com/mslinn'

For the above, the following variable values are set in development mode:

• var1: http://localhost:4444/demo_block_tag.html
• var2: http://localhost:4444/demo_inline_tag.html
• var3: https://github.com/mslinn

... and the following variable values are set in production and test modes:

• var1: https://github.com/django/django/blob/3.1.7
• var2: https://github.com/django-oscar/django-oscar/blob/3.0.2
• var3: https://github.com/mslinn

You can define additional Liquid variables in plugins built using jekyll_plugin_support. To do this, make entries in _config.yml under a key named after the value of @tag_name.

For example, let’s imagine you create a plugin using jekyll_plugin_support, and hou register it with the name phonetic_alphabet. You could define Liquid variables that would be made available to content pages in web applications that incorporate the phonetic_alphabet plugin. The following section in _config.yml defines variables called x, y and z, with values xray, yankee and zulu, respectively:

phonetic_alphabet:
  x: xray
  y: yankee
  z: zulu

The above definitions allow you to write content pages that use those variables, like the following page containing markup:

---
layout: default
title: Variable demo
---
The letter `x` is pronounced {{x}}.
Similarly, the letters `y` and `z` are pronounced {{y}} and {{z}}.

JekyllSupport::JekyllBlock and JekyllSupport::JekyllTag subclasses automatically create error classes, named after the subclass.

For example, if you create a JekyllSupport::JekyllBlock subclass called DemoBlockTag, the automatically generated error class will be called DemoBlockTagError.

Although you could use it as you would any other error class, JekyllPluginSupport provides some helper methods. These methods fill in the page path and line number that caused the error, shorten the stack trace, log an error message, and can be used to return an HTML-friendly version of the message to the web page.

The following example is a shortened version of demo/_plugins/demo_block_tag.rb. You might want to write similar code in your rescue blocks.

class DemoBlock < JekyllSupport::JekyllBlock
  VERSION = '0.1.2'.freeze

  def render_impl(text)
    raise DemoBlockTagError, 'Fall down, go boom.'
  rescue DemoBlockTagError => e
    @logger.error e.logger_message
    exit! 1 if @die_on_demo_block_error

    e.html_message
  end
end

Error class methods have been provided for standardized and convenient error handling:

• shorten_backtrace - most of the lines that spew from a Jekyll backtrace are uninteresting.
• logger_message - The message is constructed from the string provided when the error was raised, with the page path and line number added.
• html_message - The same as logger_message, but constructed with HTML.

When each tag is registered, it self-reports, for example:

INFO PluginMetaLogger: Loaded plugin demo_inline_tag v0.1.2. It has:
  Error class: DemoTagError
  CSS class for error messages: demo_tag_error

  _config.yml contains the following configuration for this plugin:
    {"die_on_demo_tag_error"=>false, "die_on_standard_error"=>false}


INFO PluginMetaLogger: Loaded plugin demo_inline_tag_no_arg v0.1.0. It has:
  Error class: DemoTagNoArgsError
  CSS class for error messages: demo_tag_no_args_error

  _config.yml does not contain configuration information for this plugin.
  You could add a section containing default values by specifying a section for the tag name,
  and an entry whose name starts with `die_on_`, followed by a snake_case version of the error name.

    demo_inline_tag_no_arg:
      die_on_demo_tag_no_args_error: false

If your tag or block plugin only needs access to the raw arguments passed from the web page, without tokenization, and you expect that the plugin might be invoked with large amounts of text, derive your plugin from JekyllBlockNoArgParsing or JekyllTagNoArgParsing.

JekyllTag and JekyllBlock subclasses of jekyll_plugin_support can utilize the attribution option if they are published as a gem. JekyllTagNoArgParsing and JekyllBlockNoArgParsing subclasses cannot. This feature is usually only desired for JekyllBlock subclasses.

• When used as a keyword option, a default value is used for the attribution string.
• When used as a name/value option, the attribution string can be specified.

Using the attribution option cause subclasses to replace their usual output with HTML that looks like:

<div id="jps_attribute_12345" class="jps_attribute">
  <a href="https://github.com/mslinn/jekyll_outline">
    <b>Generated by <code>jekyll_outline</code>.
  </a>
</div>

The id attribute is in the sample HTML above is randomized so more than one attribution can appear on a page.

You can decide where you want the attribution string for your Jekyll tag to appear by invoking @helper.attribute. For example, this is how the jekyll_outline tag generates output:

<<~HEREDOC
  <div class="outer_posts">
  #{make_entries(collection)&.join("\n")}
  </div>
  #{@helper.attribute if @helper.attribution}
HEREDOC

Typical usage for the attribution tag is:

{% my_block_tag attribution %}
  Content of my_block_tag.
{% endmy_block_tag %}

The normal processing of my_block_tag is augmented by interpolating the attribution format string, which is a Ruby-compatible interpolated string.

The default attribution format string is:

"Generated by the #{name} #{version} Jekyll plugin, written by #{author} #{date}."

Because jekyll_plugin_suppprt subclasses are gems, their gemfiles define values for name, version, homepage, and authors, as well as many other properties. The date property is obtained from the plugin/gem publishing date.

An alternative attribution string can be specified properties can be output using any of the above properties:

{% my_tag attribution="Generated by the #{name} #{version} Jekyll plugin, written by #{author} #{date}" %}

Jekyll plugins created using jekyll_plugin_support are implemented as Ruby classes. If you would like to create a version of an existing Jekyll plugin, you will need to subclass the plugin. In order to do that, you will need to override the plugin name and version, which are defined as constants.

Jekyll_plugin_support provides a method that allows a constant to be redefined, called redef_without_warning. Use it in a subclass like this:

redef_without_warning :PLUGIN_NAME, 'my_plugin'.freeze
redef_without_warning :VERSION, '0.1.0'.freeze

After checking out the jekyll_plugin_suppprt repository, run bin/setup to install dependencies.

bin/console provides an interactive prompt that allows you to experiment.

To build and install this gem onto your local machine, run:

$ bundle exec rake install
jekyll_plugin_support 0.1.0 built to pkg/jekyll_plugin_support-0.1.0.gem.
jekyll_plugin_support (0.1.0) installed.

Examine the newly built gem:

$ gem info jekyll_plugin_support

*** LOCAL GEMS ***

jekyll_plugin_support (0.1.0)
    Author: Mike Slinn
    Homepage:
    https://github.com/mslinn/jekyll_plugin_support
    License: MIT
    Installed at: /home/mslinn/.gems

    Provides support for writing Jekyll plugins.

A pry breakpoint will be set in the StandardError handler if pry_on_standard_error: true is set in variable configuration section of _config.yml.

For example, if your plugin is called blah, enable the breakpoint with the following section:

blah:
  pry_on_standard_error: true

A demo / test website is provided in the demo directory. It can be used to debug the plugin or to run freely.

1. Run from the command line:

   $ demo/_bin/debug -r

2. View the generated website, which might be at http://localhost:4444, depending on how you configured it.

1. Set breakpoints in Visual Studio Code.

2. Initiate a debug session from the command line by running the demo/_bin/debug script:

   $ demo/_bin/debug
   Fetching gem metadata from https://rubygems.org/..........
   Resolving dependencies...
   Fetching public_suffix 5.0.4
   Fetching nokogiri 1.15.5 (x86_64-linux)
   Installing public_suffix 5.0.4
   Installing nokogiri 1.15.5 (x86_64-linux)
   Bundle complete! 17 Gemfile dependencies, 96 gems now installed.
   Use `bundle info [gemname]` to see where a bundled gem is installed.
   
   INFO PluginMetaLogger: Loaded DraftFilter plugin.
   INFO PluginMetaLogger: Loaded outline_js v1.2.1 plugin.
   INFO PluginMetaLogger: Loaded outline v1.2.1 plugin.
   Configuration file: /mnt/f/jekyll_plugin_support/demo/_config.yml
             Cleaner: Removing /mnt/f/jekyll_plugin_support/demo/_site...
             Cleaner: Removing /mnt/f/jekyll_plugin_support/demo/.jekyll-metadata...
             Cleaner: Removing /mnt/f/jekyll_plugin_support/demo/.jekyll-cache...
             Cleaner: Nothing to do for .sass-cache.
   DEBUGGER: Debugger can attach via TCP/IP (127.0.0.1:37177)
   DEBUGGER: wait for debugger connection...

3. Once the DEBUGGER: wait for debugger connection... message appears, run the Visual Studio Code launch configuration called Attach with rdbg.

4. View the generated website, which might be at http://localhost:4444, depending on how you configured it.

To release a new version:

1. Update the version number in version.rb.

2. Add an entry to CHANGELOG.md describing the changes since the previous version.

3. Commit all changes to git; if you don't the next step might fail with an unexplainable error message.

4. Run the following:

   $ bundle exec rake release

   The above creates a git tag for the version, commits the created tag, and pushes the new .gem file to RubyGems.org.

1. Fork the project
2. Create a descriptively named feature branch
3. Add your feature
4. Submit a pull request

The gem is available as open source under the terms of the MIT License.