One of the large changes for 2.16 was the templatisation of the entire user-facing UI, using the Template Toolkit. Administrators can now configure the look and feel of Bugzilla without having to edit Perl files or face the nightmare of massive merge conflicts when they upgrade to a newer version in the future.
Templatisation also makes localised versions of Bugzilla possible, for the first time. In the future, a Bugzilla installation may have templates installed for multiple localisations, and select which ones to use based on the user's browser language setting.
There are two different ways of editing of Bugzilla's templates, and which you use depends mainly on how you upgrade Bugzilla. The template directory structure is that there's a top level directory, template, which contains a directory for each installed localisation. The default English templates are therefore in en. Underneath that, there is the default directory and optionally the custom directory. The default directory contains all the templates shipped with Bugzilla, whereas the custom directory does not exist at first and must be created if you want to use it.
The first method of making customisations is to directly edit the templates in template/en/default. This is probably the best method for small changes if you are going to use the CVS method of upgrading, because if you then execute a cvs update, any template fixes will get automagically merged into your modified versions.
If you use this method, your installation will break if CVS conflicts occur.
The other method is to copy the templates into a mirrored directory structure under template/en/custom. The templates in this directory automatically override those in default. This is the technique you need to use if you use the overwriting method of upgrade, because otherwise your changes will be lost. This method is also better if you are using the CVS method of upgrading and are going to make major changes, because it is guaranteed that the contents of this directory will not be touched during an upgrade, and you can then decide whether to continue using your own templates, or make the effort to merge your changes into the new versions by hand.
If you use this method, your installation may break if incompatible changes are made to the template interface. If such changes are made they will be documented in the release notes, provided you are using a stable release of Bugzilla. If you use using unstable code, you will need to deal with this one yourself, although if possible the changes will be mentioned before they occur in the deprecations section of the previous stable release's release notes.
Don't directly edit the compiled templates in data/template/* - your changes will be lost when Template Toolkit recompiles them.
The syntax of the Template Toolkit language is beyond the scope of this guide. It's reasonably easy to pick up by looking at the current templates; or, you can read the manual, available on the Template Toolkit home page. However, you should particularly remember (for security reasons) to always HTML filter things which come from the database or user input, to prevent cross-site scripting attacks.
However, one thing you should take particular care about is the need to properly HTML filter data that has been passed into the template. This means that if the data can possibly contain special HTML characters such as <, and the data was not intended to be HTML, they need to be converted to entity form, ie <. You use the 'html' filter in the Template Toolkit to do this. If you fail to do this, you may open up your installation to cross-site scripting attacks.
Also note that Bugzilla adds a few filters of its own, that are not in standard Template Toolkit. In particular, the 'url_quote' filter can convert characters that are illegal or have special meaning in URLs, such as &, to the encoded form, ie %26. This actually encodes most characters (but not the common ones such as letters and numbers and so on), including the HTML-special characters, so there's never a need to HTML filter afterwards.
Editing templates is a good way of doing a "poor man's custom fields". For example, if you don't use the Status Whiteboard, but want to have a free-form text entry box for "Build Identifier", then you can just edit the templates to change the field labels. It's still be called status_whiteboard internally, but your users don't need to know that.
If you are making template changes that you intend on submitting back for inclusion in standard Bugzilla, you should read the relevant sections of the Developers' Guide.
Some CGIs have the ability to use more than one template. For example, buglist.cgi can output bug lists as RDF or two different forms of HTML (complex and simple). (Try this out by appending &format=simple to a buglist.cgi URL on your Bugzilla installation.) This mechanism, called template 'formats', is extensible.
To see if a CGI supports multiple output formats, grep the CGI for "ValidateOutputFormat". If it's not present, adding multiple format support isn't too hard - see how it's done in other CGIs.
To make a new format template for a CGI which supports this, open a current template for that CGI and take note of the INTERFACE comment (if present.) This comment defines what variables are passed into this template. If there isn't one, I'm afraid you'll have to read the template and the code to find out what information you get.
Write your template in whatever markup or text style is appropriate.
You now need to decide what content type you want your template served as. Open up the localconfig file and find the $contenttypes variable. If your content type is not there, add it. Remember the three- or four-letter tag assigned to you content type. This tag will be part of the template filename.
Save the template as <stubname>-<formatname>.<contenttypetag>.tmpl. Try out the template by calling the CGI as <cginame>.cgi?format=<formatname> .
There are a few templates you may be particularly interested in customising for your installation.
index.html.tmpl: This is the Bugzilla front page.
global/header.html.tmpl: This defines the header that goes on all Bugzilla pages. The header includes the banner, which is what appears to users and is probably what you want to edit instead. However the header also includes the HTML HEAD section, so you could for example add a stylesheet or META tag by editing the header.
global/banner.html.tmpl: This contains the "banner", the part of the header that appears at the top of all Bugzilla pages. The default banner is reasonably barren, so you'll probably want to customise this to give your installation a distinctive look and feel. It is recommended you preserve the Bugzilla version number in some form so the version you are running can be determined, and users know what docs to read.
global/footer.html.tmpl: This defines the footer that goes on all Bugzilla pages. Editing this is another way to quickly get a distinctive look and feel for your Bugzilla installation.
bug/create/user-message.html.tmpl: This is a message that appears near the top of the bug reporting page. By modifying this, you can tell your users how they should report bugs.
bug/create/create.html.tmpl and bug/create/comment.txt.tmpl: You may wish to get bug submitters to give certain bits of structured information, each in a separate input widget, for which there is not a field in the database. The bug entry system has been designed in an extensible fashion to enable you to define arbitrary fields and widgets, and have their values appear formatted in the initial Description, rather than in database fields. An example of this is the mozilla.org guided bug submission form.
To make this work, create a custom template for enter_bug.cgi (the default template, on which you could base it, is create.html.tmpl), and either call it create.html.tmpl or use a format and call it create-<formatname>.html.tmpl. Put it in the custom/bug/create directory. In it, add widgets for each piece of information you'd like collected - such as a build number, or set of steps to reproduce.
Then, create a template like custom/bug/create/comment.txt.tmpl, also named after your format if you are using one, which references the form fields you have created. When a bug report is submitted, the initial comment attached to the bug report will be formatted according to the layout of this template.
For example, if your enter_bug template had a field
<input type="text" name="buildid" size="30">
BuildID: [% form.buildid %]