Extending Kate with Scripts

As mentioned in one of my last blogs, there has been quite some work for JavaScript scripting support in trunk recently. So what will Kate 3.4 (KDE 4.4) will bring? This is explained in detail in the sections:

  • Indentation Scripting
  • Command Line Scripting
  • Some Remarks

The scripting allows to extend Kate with lots of little helper functions. All users can add scripts as they wish. The documentation here is copied from the official Kate handbook. So instead of using this blog as reference, please use the handbook later for an up-to-date version. To script something useful, you’ll need to know the scripting API. All the available functions are documented in the section Scripting API in the handbook as well. Enough said, here we go:

Extending Kate with Scripts

Since Kate 3.4 in KDE 4.4 the Kate editor component is easily extensible by writing scripts. The scripting language is ECMAScript (widely known as JavaScript). Kate supports two kinds of scripts: indentation and command line scripts.

Indentation Scripts

Indentation scripts – also referred as indenters – automatically indent the source code while typing text. As example, after hitting the return-key code the indentation level often increases.

The following sections describe step by step how to create the skeleton for a simple indenter. As first step, create a new *.js file called e.g. javascript.js in the local home folder $KDEHOME/share/apps/katepart/script.

The Indentation Script Header

The header of the file javascript.js is embedded in a comment and is of the following form

/* kate-script
 * name: JavaScript
 * author: Example Name
 * license: BSD
 * revision: 1
 * kate-version: 3.4
 * type: indentation
 * required-syntax-style: javascript
 * indent-languages: javascript
 * priority: 0
 *
 * A line without colon ':' stops header parsing. That is, you can add optional
 * text here such as a detailed license.
 */

Each entry is explained in detail now:

  • kate-script [required]: This text string has to appear in the first line of the *.js file, otherwise Kate skips the script.
  • name [required]: This is the indenter name that appears in the menu Tools->Indentation and in the configuration dialog.
  • author [optional]: The author’s name and contact information.
  • license [optional]: Short form of the license, such as BSD or LGPLv3.
  • revision [required]: The revision of the script. This number should be increased whenever the script is modified.
  • kate-version [required]: Minimal required Kate version.
  • type [required]: The type must be “indentation”, otherwise Kate skips this script.
  • required-syntax-style [optional]: Comma separated list of required syntax highlighting styles. This is important for indenters that rely on specific highlight information in the document. If a required syntax style is specified, the indenter is available only when the appropriate highlighter is active. This prevents “undefined behavior” caused by using the indenter without the expected highlighting schema. For instance, the Ruby indenter makes use of this in the files ruby.js and ruby.xml.
  • indent-languages [optional]: Comma separated list of syntax styles the indenter can indent correctly, e.g.: c++, java.
  • priority [optional]: If several indenters are suited for a certain highlighted file, the priority decides which indenter is chosen as default indenter.

Kate reads all pairs of the form “key:value” until it cannot fine a colon anymore. This implies that the header can contain arbitrary text such as a license as shown in the example.

The Indenter Source Code

Having specified the header this section explains how the indentation scripting itself works. The basic skeleton of the body looks like this:

triggerCharacters = "{}/:;";
function indent(line, indentWidth, ch)
{
  // called for each newline (ch == '\n') and all characters specified in
  // the global variable triggerCharacters. When calling Tools -> Align
  // the variable ch is empty, i.e. ch == ''.
  //
  // see also: Scripting API
  return -2;
}

The function indent() has three parameters:

  • line: the line that has to be indented
  • indentWidth: the indentation width in amount of spaces
  • ch: either a newline character (ch == '\n'), the trigger character specified in triggerCharacters or empty if the user invoked the action Tools->Align.

The return value of the indent() function specifies how the line will be indented. If the return value is a simple integer number, it is interpreted as follows:

  • return value -2: do nothing
  • return value -1: keep indentation (searches for previous non-blank line)
  • return value 0: numbers >= 0 specify the indentation depth in spaces

Alternatively, an array of two elements can be returned:

  • return [ indent, align ];

In this case, the first element is the indentation depth like above with the same meaning of the special values. However, the second element is an absolute value representing a column for “alignment”. If this value is higher than the indent value, the difference represents a number of spaces to be added after the indentation of the first parameter. Otherwise, the second number is ignored. Using tabs and spaces for indentation is often referred to as “mixed mode”.

Consider the following example: Assume using tabs to indent, and tab width is set to 4. Here, <tab> represents a tab and ‘.’ a space:

1: <tab><tab>foobar("hello",
2: <tab><tab>......."world");

When indenting line 2, the indent() function returns [8, 15]. As result, two tabs are inserted to indent to column 8, and 7 spaces are added to align the second parameter under the first, so that it stays aligned if the file is viewed with a different tab width.

A default KDE installation ships Kate with several indenters. The corresponding JavaScript source code can be found in $KDRDIR/share/apps/katepart/script.

Developing an indenter requires to reload the scripts to see whether the changes behave appropriately. Instead of restarting the application, simply switch to the command line and invoke the command reload-scripts.

If you develop useful scripts please consider contributing to the Kate Project by contacting the mailing list.

Command Line Scripts

As it is hard to satisfy everyone’s needs, Kate supports little helper tools for quick text manipulation through the built-in command line. For instance, the command sort is implemented as script. This section explains how to create *.js files to extend Kate with arbitrary helper scripts.

Command line scripts are located in the save folder as indentation scripts. So as first step, create a new *.js file called myutils.js in the local home folder $KDEHOME/share/apps/katepart/script.

The Command Line Script Header

The header of each command line script is embedded in a comment and is of the following form

/* kate-script
 * author: Example Name
 * license: BSD
 * revision: 1
 * kate-version: 3.4
 * type: commands
 * functions: sort, format-paragraph
 *
 * A line without colon ':' stops header parsing. That is, you can add optional
 * text here such as a detailed license.
 */

Each entry is explained in detail now:

  • kate-script [required]: This text string has to appear in the first line of the *.js file, otherwise Kate skips the script.
  • author [optional]: The author’s name and contact information.
  • license [optional]: Short form of the license, such as BSD or LGPLv3.
  • revision [required]: The revision of the script. This number should be increased whenever the script is modified.
  • kate-version [required]: Minimal required Kate version.
  • type [required]: The type must be ‘commands’, otherwise Kate skips this script.
  • functions [required]: Comma separated list of commands in the script.

Kate reads all pairs of the form “key:value” until it cannot fine a colon anymore. This implies that the header can contain arbitrary text such as a license as shown in the example. The value of the key functions is a comma separated list of command line commands. This means a single script contains an arbitrary amount of command line commands. Each function is available through Kate‘s built-in command line.

The Script Source Code

All functions specified in the header have to be implemented in the script. For instance, the script file from the example above needs to implement the two functions sort and format-paragraph. All functions have the following syntax:

function (arg1, arg2, ...) {
  // ... implementation, see also: Scripting API
}

Arguments in the command line are passed to the function as arg1, arg2, etc. In order to provide documentation for each command, simply implement the ‘help‘ function as follows:

function help(cmd)
{
  if (cmd == "sort") {
    return "Sort the selected text.";
  } else if (cmd == "...") {
    // ...
  }
}

Executing help sort in the command line then calls this help function with the argument cmd set to the given command, i.e. cmd == "sort". Kate then presents the returned text as documentation to the user.

Developing a command line script requires to reload the scripts to see whether the changes behave appropriately. Instead of restarting the application, simply switch to the command line and invoke the command reload-scripts.

If you develop useful scripts please consider contributing to the Kate Project by contacting the mailing list.

Final Remarks

The command line scripting can be accessed for all KTextEditor users through the KTextEditor::CommandInterface. That is, you can query a specific command and execute it with arbitrary parameters (The parameter cmd contains the command itself including all arguments. Example: cmd = “goto 65″).

Kate’s command line itself is actually a quite powerful tool. It’s a little bit sad that it’s rather unknown. If you want to know more, just invoke “View -> Swith to command line” (shortcut: F7) and start typing text. More details are in the Kate handbook as well.

The Kate scripting API can be found here.

first experience with Archlinux

So, I kinda messed up my desktop right after the upgrade to karmic, because I was too greedy for performance and converted my root file system to ext4. Well, that worked like a charm on my laptop, but it broke my desktop. This is in no way karmic’s fault, it’s my own misbehavior. Thankfully I could rescue most of my data.

Since I’d had to reinstall anyways, I decided to finally try out Archlinux. I find the rolling release mantra very intriguing. Together with a “simpler” packaging, namely no splitting between -dev and -dbg packages like debian/ubuntu does, this is destined to be a good environment for a developer. I always hated it to track down missing -dev packages when compiling software. And don’t get me started on outdated software in repos… I just compiled kdelibs and the only missing build dependency was hspell, that I don’t need anyways. Under Jaunty I had to compile stuff from kdesupport to fulfill updated dependencies. And the list of not-found optional dependencies was huge, since I did not spent time to install all those -dev packages by hand…

My first impression of Archlinux is very good so far. I also finally migrated to 64bit wich works like a charm, no issues with flash or anything. Since I never used a 64bit Ubuntu/Debian I’m not sure, whether the perceived performance increase is due to the switch to 64bit or whether Archlinux optimized packages are responsible. Probably both. Nevertheless I can safely say that my system feels snappier than before.

Of course, the installation and initial setup is not as straight forward / easy as with Debian/Ubuntu: Yet it’s no big deal for anyone with some Linux experience. And, once everything is setup, you are running KDE again, so no real difference. Thanks to the Chakra team for kdemod, it works like a charm!

I might have spent a bit more time during the installation / initial configuration, but I think this would have happened also if I’d installed any other distro I’ve never used before, like OpenSuse or Fedora.

Oh and since I can install sudo I can keep my old habits. Neat.

The only thing I miss so far is aptitude with it’s straight forward command structure. Yaourt/Pacman is fast and nice, esp. with pacman-color, but the commands don’t feel as straight forward to me… Personal preference I’d say.

To conclude: Archlinux is very nice, I can wholeheartedly recommend using it so far. Probably nothing for a novice Linux user, yet perfect for advanced users. Very good as a development environment. Fast. Up to date. I like it :)

Now I can finally continue hacking on Kate/Kdelibs again :) I’m currently in the process of refactoring Kate’s implementation of the TemplateInterface. Even in it’s current state it already implements features like mirrored snippets and the like. But once I’ve finished with the cleanup I will try to implement some more of the features that are found in e.g. yasnippet for Emacs. I really wonder why nobody else did that already…

Once this is finished, you can expect that I will deeply integrate that feature in various places in KDevelop, especially for code completion, snippet plugin etc. pp. Stay tuned!

News from the Holy Kate Land

Since we now all know that Kate is holy (thanks to rms. By accident, he obviously confused Kate with emacs, though) let’s have a look at what’s going on. In the last months Kate development is quite active, so here is a quick update:

  • new: on-the-fly spell checking thanks to Michel Ludwig. Highlights include e.g. spell checking in comments of source code or latex parts. Also, constructs like sch\”on work in latex.
  • extended scripting support in the command line, more on that later
  • more and more mature vi input mode
  • lots of bug fixing. quite impressive bug squashing by Pascal Létourneau for more than 4 months now
  • lots of refactoring and code cleanups thanks to Bernhard!
  • “Find in Files” appears by default again in the tool view,
  • “File Browser” uses UrlNavigator, huge code cleanup
  • convenience updates of syntax highlighting
  • delayed highlighting of code folding ranges to prevent flickering on mouse move
  • new command line commands: ‘toggle-header’ in the Open Header plugin. ‘grep’ and ‘find-in-files’
  • haskell and lilypond indenter
  • much, much more, see commits for details.

Thanks to all contributors involved in Kate development. Keep it up :)

Improved PHP support in Kate

Not only KDevelop gets better and better PHP support — the Kate PHP syntax file also got a few new features and fixes over the last weeks. The good thing is of course that all users of KWrite, Kate, Quanta, KDevelop and other editors leveraging the Katepart benefit from these changes.

Improved HereDocs

screenshot of improved highlighting in PHP heredocs
screenshot of improved highlighting in PHP heredocs

I went over PHP related bugs on bugs.kde.org today and spotted one that was fairly easy to fix:

vim-like syntax highlighting support for heredocs in php.xml

With some magic (IncludeRules just rocks) I got it working fairly easy. You can see the results to the right.

Additionally I added code folding to heredocs, since often these strings include lots of text and hiding it often makes sense.

Better support for overlapping syntax regions

code folding with overlapping syntax regions
code folding with overlapping syntax regions

Another long standing bug (accommodate overlapping syntax regions (especially for php)) got fixed by James Sleeman.

Finally PHP templates with code such as

  1. <?php if ( true ) : ?>
  2. <!-- some html stuff -->
  3. <?php elseif ( false ) { ?>
  4. <!-- some other html stuff -->
  5. <?php } ?>

can be folded properly. This kind of spaghetti code is used quite often in simple templates and having the posibility to fold it properly is a huge win in my opinion. Thanks to James Sleeman again!