Template Toolkit Plugin

This is a rather slim glue to Andy Wardley's Template Toolkit (see http://www.template-toolkit.org/ or TWiki:Codev.TemplateToolkit for more, though the latter is pretty stale).

I myself have here and then argued that TT is too heavyweight for use as a template system for TWiki, but this does only prevent using TT as the only template system for TWiki.

If, on the other hand, you do have TT installed anyway, and especially if you have it running in a mod_perl environment where module compilation time is no longer an issue, then you might want to share your TT blocks or layouts with TWiki.

The implementation as a plugin does not allow to install TT as a drop-in replacement for TWiki's own templating system. But I think that for first experiments it is possible to emulate that: Use very slim TWiki templates to get TWiki's template system out of the way, and run your topics through TT instead.

To be honest, I am using this plugin as both a first step to evaluate TT as a TWiki template machine, and as a real-life hands-on example for BenchmarkContrib to play with.

Syntax Rules

The plugin has just one TWiki tag in the TWiki sense:

• Syntax example: %TEMPLATETOOLKIT{"on" WRAPPER="myTTtemplate.tt2"}%
• If present in a topic with a value of "on", the whole topic will be processed by TT.
• A configuration variable named $TWiki::cfg{Plugins}{TemplateToolkitPlugin}{UseTT} can be used to set a site-wide default
• Supported Parameters:

  Parameter:	Description:	Default:
  "on" / "off"	Switch to control TT usage for the current topic. A value "on" or "1" will activate TT processing for the current topic, every other value will disable it. To retain the configuration setting, don't specify this parameter.	Config variable {UseTT}
  WRAPPER="tt_template"	The TT wrapper template into which the topic will be embedded. The wrapper must explicitly include the topic content, which is available as a TT variable [% content %].	no wrapper

Configuration Variables

Not fully documented, until I figure out how http://www.torontowikituesdays.com/twiki/bin/configure will pick up plugin configuration vars.

All configuration variables for this plugin are collected under $TWiki::cfg{Plugins}{TemplateToolkitPlugin}.

Notes on Template Toolkit Syntax

If you are familiar with the Template Toolkit, then you surely know that it per default embeds its directives between the delimiters [% and %]. As almost everything in TT this is configurable, but the default delimiters are used quite frequently because they usually don't occur in "normal text". Usually. In TWiki, there is a syntax construction which is quite popular, but makes TT croak: Forced links, with an embedded TWiki variable. Example:

[[%SYSTEMWEB%.%STATISTICSTOPIC%]]

This plugin tries hard to cope with this, so the above example will work as intended. Some recommendations, just in case:

• It is good practice to write your TT constructs as [% tt_directive %], i.e. with surrounding spaces around directives. By doing so, you'll make sure to never clash with a possible TWiki variable name %tt_directive%.
• Separate TT stuff from heavy TWiki lifting or you'll get severe bracketiquotitis.
• If you want to use different delimiters, define both {TToptions}{START_TAG} and {TToptions}{END_TAG} in $TWiki::cfg{Plugins}{TemplateToolkitPlugin}.
• When writing TT wrappers for use with this plugin, keep in mind that they are TT-expanded, but not TML-processed.

Examples

Per default, TemplateToolkitPlugin ships with a simple TT demo wrapper. To see it in action, prepend a topic with the following line:

%TEMPLATETOOLKIT{"on" WRAPPER="demowrapper.tt2"}%

TT expansion can be controlled by URL parameters as well. If the plugin is installed, you can apply the demonstration wrapper to the current topic by clicking here.

Security Considerations

Unlike in typical TT web applications, in a TWiki many people can edit the templates, and so they can introduce TT directives. To keep your TWiki unharmed, some precautions should be made:

1. Do not enable EVAL_PERL (it is off per default).
2. Do not pass critical data structures like the configuration hash as TT variables. Remember that with TT directives it is possible to change data, and to call object methods. With a persistent interpreter like mod_perl, this could lead to a corrupt configuration for subsequent requests.

Future Directions

If time permits, I'll try to:

• create a TWiki skin and a TT layout in parallel and run benchmarks on both.
• document (and extend) configuration items
• Add a TWiki filter for TT templates so that wrappers can use TWiki variables
• ...

Plugin Installation Instructions

%$INSTALL_INSTRUCTIONS%

Plugin Info

Related Topics: TWikiPlugins, DeveloperDocumentationCategory, AdminDocumentationCategory, TWikiPreferences

-- TWiki:Main.HaraldJoerg - 21 Sep 2006