Language highlighting

Highlight.js

Discourse has the ability to use highlight.js to do source code highlighting within a post. As this feature is CPU intensive, Discourse has an admin option to select which programming languages can be used with code blocks; see examples below.

If you use the fence ``` without a name it will default to Prolog.
If you don’t want any highlighting then use plaintext


Examples

Prolog

```prolog
<code> 
```
reverse(List, Reversed) :-
          reverse(List, [], Reversed).

reverse([], Reversed, Reversed).
reverse([Head|Tail], SoFar, Reversed) :-
          reverse(Tail, [Head|SoFar], Reversed).

Augmented Backus-Naur Form

```abnf
<code> 
```
; line comment

ruleset     =   [optional] *(group1 / group2 / SP) CRLF ; trailing comment

group1      =   alt1
group1      =/  alt2

alt1        =   %x41-4D / %d78-90

alt2        =   %b00100001

group2      =   *1DIGIT / 2*HEXDIG / 3*4OCTET

optional    =   hex-codes
                / literal
                / sensitive
                / insensitive

hex-codes   =   %x68.65.6C.6C.6F
literal     =   "string literal"
sensitive   =   %s"case-sensitive string"
insensitive =   %i"case-insensitive string"

BASH

```bash
<code> 
```
#!/bin/bash

###### CONFIG
ACCEPTED_HOSTS="/root/.hag_accepted.conf"
BE_VERBOSE=false

if [ "$UID" -ne 0 ]
then
 echo "Superuser rights required"
 exit 2
fi

genApacheConf(){
 echo -e "# Host ${HOME_DIR}$1/$2 :"
}

echo '"quoted"' | tr -d \" > text.txt

BNF ( Backus–Naur Form)

```bnf
<code> 
```
<syntax>         ::= <rule> | <rule> <syntax>
<rule>           ::= <opt-whitespace> "<" <rule-name> ">" <opt-whitespace> "::=" <opt-whitespace> <expression> <line-end>
<opt-whitespace> ::= " " <opt-whitespace> | ""
<expression>     ::= <list> | <list> <opt-whitespace> "|" <opt-whitespace> <expression>
<line-end>       ::= <opt-whitespace> <EOL> | <line-end> <line-end>
<list>           ::= <term> | <term> <opt-whitespace> <list>
<term>           ::= <literal> | "<" <rule-name> ">"
<literal>        ::= '"' <text> '"' | "'" <text> "'"

CMake

```cmake
<code> 
```
cmake_minimum_required(VERSION 2.8.8)
project(cmake_example)

# Show message on Linux platform
if (${CMAKE_SYSTEM_NAME} MATCHES Linux)
    message("Good choice, bro!")
endif()

# Tell CMake to run moc when necessary:
set(CMAKE_AUTOMOC ON)
# As moc files are generated in the binary dir,
# tell CMake to always look for includes there:
set(CMAKE_INCLUDE_CURRENT_DIR ON)

# Widgets finds its own dependencies.
find_package(Qt5Widgets REQUIRED)

add_executable(myproject main.cpp mainwindow.cpp)
qt5_use_modules(myproject Widgets)

C++

```cpp
<code> 
```
#include <iostream>

int main(int argc, char *argv[]) {

  /* An annoying "Hello World" example */
  for (auto i = 0; i < 0xFFFF; i++)
    cout << "Hello, World!" << endl;

  char c = '\n';
  unordered_map <string, vector<string> > m;
  m["key"] = "\\\\"; // this is an error

  return -2e3 + 12l;
}

CSS

```css
<code> 
```
@font-face {
  font-family: Chunkfive; src: url('Chunkfive.otf');
}

body, .usertext {
  color: #F0F0F0; background: #600;
  font-family: Chunkfive, sans;
  --heading-1: 30px/32px Helvetica, sans-serif;
}

@import url(print.css);
@media print {
  a[href^=http]::after {
    content: attr(href)
  }
}

Diff

```diff
<code> 
```
Index: languages/ini.js
===================================================================
--- languages/ini.js    (revision 199)
+++ languages/ini.js    (revision 200)
@@ -1,8 +1,7 @@
 hljs.LANGUAGES.ini =
 {
   case_insensitive: true,
-  defaultMode:
-  {
+  defaultMode: {
     contains: ['comment', 'title', 'setting'],
     illegal: '[^\\s]'
   },

*** /path/to/original timestamp
--- /path/to/new      timestamp
***************
*** 1,3 ****
--- 1,9 ----
+ This is an important
+ notice! It should
+ therefore be located at
+ the beginning of this
+ document!

! compress the size of the
! changes.

  It is important to spell

HTML

```xml
<code> 
```
<!DOCTYPE html>
<title>Title</title>

<style>body {width: 500px;}</style>

<script type="application/javascript">
  function $init() {return true;}
</script>

<body>
  <p checked class="title" id='title'>Title</p>
  <!-- here goes the rest of the page -->
</body>

ini

```ini
<text> 
```
; boilerplate
[package]
name = "some_name"
authors = ["Author"]
description = "This is \
a description"

[[lib]]
name = ${NAME}
default = True
auto = no
counter = 1_000

Java

```java
<code> 
```
/**
 * @author John Smith <john.smith@example.com>
*/
package l2f.gameserver.model;

public abstract strictfp class L2Char extends L2Object {
  public static final Short ERROR = 0x0001;

  public void moveTo(int x, int y, int z) {
    _ai = null;
    log("Should not be called");
    if (1 > 5) { // wtf!?
      return;
    }
  }
}

JavaScript

```javascript
<code> 
```
function $initHighlight(block, cls) {
  try {
    if (cls.search(/\bno\-highlight\b/) != -1)
      return process(block, true, 0x0F) +
             ` class="${cls}"`;
  } catch (e) {
    /* handle exception */
  }
  for (var i = 0 / 2; i < classes.length; i++) {
    if (checkCondition(classes[i]) === undefined)
      console.log('undefined');
  }

  return (
    <div>
      <web-component>{block}</web-component>
    </div>
  )
}

export  $initHighlight;

JSON

```json
<code> 
```
[
  {
    "title": "apples",
    "count": [12000, 20000],
    "description": {"text": "...", "sensitive": false}
  },
  {
    "title": "oranges",
    "count": [17500, null],
    "description": {"text": "...", "sensitive": false}
  }
]

LaTeX

```latex
<code> 
```
\documentclass{article}
\usepackage[koi8-r]{inputenc}
\hoffset=0pt
\voffset=.3em
\tolerance=400
\newcommand{\eTiX}{\TeX}
\begin{document}
\section*{Highlight.js}
\begin{table}[c|c]
$\frac 12\, + \, \frac 1{x^3}\text{Hello \! world}$ & \textbf{Goodbye\~ world} \\\eTiX $ \pi=400 $
\end{table}
Ch\'erie, \c{c}a ne me pla\^\i t pas! % comment \b
G\"otterd\"ammerung~45\%=34.
$$
    \int\limits_{0}^{\pi}\frac{4}{x-7}=3
$$
\end{document}

Markdown

```markdown
<code> 
```
# hello world

you can write text [with links](http://example.com) inline or [link references][1].

* one _thing_ has *em*phasis
* two __things__ are **bold**

[1]: http://example.com

---

hello world
===========

<this_is inline="xml"></this_is>

> markdown is so cool

    so are code segments

1. one thing (yeah!)
2. two thing `i can write code`, and `more` wipee!

PostgreSQL and PL/pgSQL

```pgsql
<code> 
```
BEGIN;
SELECT sum(salary) OVER w, avg(salary) OVER w
  FROM empsalary
  WINDOW w AS (PARTITION BY depname ORDER BY salary DESC);
END;

CREATE FUNCTION days_of_week() RETURNS SETOF text AS $$
BEGIN
  FOR i IN 7 .. 13 LOOP
    RETURN NEXT to_char(to_date(i::text,'J'),'TMDy');
  END LOOP;
END;
$$ STABLE LANGUAGE plpgsql;

plaintext

```plaintext
<text> 
```
 id | description
----+-------------
  1 | one
  2 | two
  3 | three
(3 rows)

SQL

```sql
<text> 
```
CREATE TABLE "topic" (
    "id" serial NOT NULL PRIMARY KEY,
    "forum_id" integer NOT NULL,
    "subject" varchar(255) NOT NULL
);
ALTER TABLE "topic"
ADD CONSTRAINT forum_id FOREIGN KEY ("forum_id")
REFERENCES "forum" ("id");

-- Initials
insert into "topic" ("forum_id", "subject")
values (2, 'D''artagnian');

Windows DOS

AKA Command Prompt

```dos
<commands> 
```
cd \
copy a b
ping 192.168.0.1
@rem ping 192.168.0.1
net stop sharedaccess
del %tmp% /f /s /q
del %temp% /f /s /q
ipconfig /flushdns
taskkill /F /IM JAVA.EXE /T

cd Photoshop/Adobe Photoshop CS3/AMT/
if exist application.sif (
    ren application.sif _application.sif
) else (
    ren _application.sif application.sif
)

taskkill /F /IM proquota.exe /T

sfc /SCANNOW

set path = test

xcopy %1\*.* %2

YAML

```yaml
<text> 
```
---
# comment
string_1: "Bar"
string_2: 'bar'
string_3: bar
inline_keys_ignored: sompath/name/file.jpg
keywords_in_yaml:
  - true
  - false
  - TRUE
  - FALSE
  - 21
  - 21.0
  - !!str 123
"quoted_key": &foobar
  bar: foo
  foo:
  "foo": bar

reference: *foobar

multiline_1: |
  Multiline
  String
multiline_2: >
  Multiline
  String
multiline_3: "
  Multiline string
  "

ansible_variables: "foo {{variable}}"

array_nested:
- a
- b: 1
  c: 2
- b
- comment

I don’t see the syntax highlighting for Java/JavaScript/dos/cpp/bash or python. The only ones that are highlighted for me are: Prolog and Json,.

I had to do a refresh of the site before I saw the styling on the other languages as well, but now they’re showing up for me.

1 Like

Thanks, I was able to see it working.

1 Like