SwarmLab-HowTos/labs/Howtos/asciidoc/_includes/src-pygments.adoc

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Included in:

- user-manual: Source Code Syntax Highlighting: Pygments installation
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{pygments-org}[Pygments] is a popular syntax highlighter that supports a broad range of {pygments-lang}[programming, template and markup languages].

In order to use Pygments with Asciidoctor, you need https://www.python.org[Python 2] and the {pygments-gem}[pygments.rb gem].

TIP: You _do not_ need to install Pygments itself.
It comes bundled with the pygments.rb gem.

IMPORTANT: You must have Python 2 installed to use pygments.rb.
Python 3 is not compatible with the pygments.rb gem.
Check that you have a `python2` (Linux), `python` (macOS), or `py -2` (Windows) executable on your PATH.
(On macOS, verify that the `python` executable uses Python 2 by running `python -V`).

.Installing Python and the pygments.rb gem via the CLI (cross platform)
[source,console]
....
$ "`\which apt-get || \which dnf || \which yum || \which brew`" install python # <1>
$ gem install pygments.rb # <2>
....
<1> Install Python using your package manager
<2> Install the pygments.rb gem

Once you've installed these libraries, assign `pygments` to the `source-highlighter` attribute in your document's header.

[source]
----
:source-highlighter: pygments
----

You can further customize the source block output with additional Pygments attributes.

pygments-style::
Sets the name of the color theme Pygments uses.
To see the list of available style names, see <<listing-pygments-style-names>>.
Default: `pastie`.

pygments-css::
Controls what method is used for applying CSS to the tokens.
Can be `class` (CSS classes) or `style` (inline styles).
See <<user-manual#hl-css,Pygments stylesheet>> to learn more about how the value `class` is handled.
Default: `class`.

pygments-linenums-mode::
Controls how line numbers are arranged when line numbers are enabled on the source block.
Can be `table` or `inline`.
If line wrapping is enabled on preformatted blocks (i.e., `prewrap`), and you want to use line numbering on source blocks, you must set the value of this attribute to `inline` in order for the numbers to line up properly with their target lines.
Default: `table`.

.Customizing a source block with Pygments attributes
[source]
....
:source-highlighter: pygments
:pygments-style: manni
:pygments-linenums-mode: inline

[source,ruby,linenums]
----
ORDERED_LIST_KEYWORDS = {
  'loweralpha' => 'a',
  'lowerroman' => 'i',
  'upperalpha' => 'A',
  'upperroman' => 'I'
   #'lowergreek' => 'a'
   #'arabic'     => '1'
   #'decimal'    => '1'
}
----
....

.Result: Source block using inline line numbers and the manni theme
====
image::custom-pygments.png[Line numbers and a custom Pygments theme for a source block.]
====

==== Highlight Select Lines

Not to be confused with syntax highlighting, you can configure Pygments to highlight (i.e., emphasize) select lines in order to call attention to them.
This feature is activated on a source block if the highlight attribute is defined.

The highlight attribute accepts a comma or semi-colon delimited list of line ranges.
A line range is represented by two numbers separated by a double period (e.g., `2..5`).
These numbers correspond to the line numbers of the source block, inclusive, where the first line is 1.

.Highlight select lines in a source block
[source]
....
:source-highlighter: pygments

[source,ruby,highlight=2..5]
----
ORDERED_LIST_KEYWORDS = {
  'loweralpha' => 'a',
  'lowerroman' => 'i',
  'upperalpha' => 'A',
  'upperroman' => 'I',
}
----
....

[#listing-pygments-style-names]
==== Available Pygments style names

To list the available Pygments styles, run the following command in a terminal:

 $ $(dirname $(gem which pygments.rb))/../vendor/pygments-main/pygmentize -L styles

The pygments.rb gem uses a bundled version of Pygments (often ahead of the latest release).
This command ensures that you are invoking the `pygmentize` command from the Pygments used by that gem.

==== Using a custom Pygments installation

If you already have Pygments installed on your system, you want to use your own fork, or you want to customize how Pygments is configured, you can get Asciidoctor to use a custom version of Pygments instead of the one bundled with the pygments.rb gem.

First, install your own version of Pygments.
You can do this, for instance, by cloning the upstream Pygments repository:

 $ hg clone https://bitbucket.org/birkenfeld/pygments-main pygments

Find the directory that contains the file [.path]_pygmentize_ or the [.path]_Makefile_.
That's your Pygments installation path.
Make note of it.

Next, create a script to run _before_ invoking Asciidoctor for the first time.
Let's call it [.path]_pygments_init.rb_.
Populate the script with the following content:

.pygments_init.rb
[source,ruby]
----
require 'pygments'

# use a custom Pygments installation (directory that contains pygmentize)
Pygments.start '/path/to/pygments'

# example of registering a missing or additional lexer
#Pygments::Lexer.create name: 'Turtle', aliases: ['turtle'],
#    filenames: ['*.ttl'], mimetypes: ['text/turtle', 'application/x-turtle']
----

TIP: You could enhance this script to read the Pygments installation path from an environment variable (or configuration file).

Now just require this script before your invoke Asciidoctor the first time.
When using the `asciidoctor` command, pass the script using the `-r` flag:

 $ asciidoctor -r ./pygments_init.rb document.adoc

When using the Asciidoctor API, require the script using `require` or `require_relative`:

[source,ruby]
----
require 'asciidoctor'
require_relative './pygments_init.rb'

Asciidoctor.convert_file 'document.adoc', safe: :safe
----

Now Asciidoctor is using your custom installation of Pygments instead of the one bundled with the pygments.rb gem.