{{{#!div class="important" style="padding: 0em 2em; margin: 2em 0" ** Warning ** The following documentation corresponds to an experimental branch ([[Proposals/Jinja]]; Git branch: [log:cboos.git@jinja2] - [https://github.com/cboos/trac.git github mirror]). }}} [[PageOutline(2-4)]] = Porting Templates from Genshi to Jinja2 The following documentation is primarily targeted at plugin developers who wish to adapt their Genshi templates to the Jinja2 template engine that will be used in Trac 1.4. For migrating your own templates, a good way to start is to learn from examples. Compare the 'j...' Jinja templates found in source:cboos.git/trac/templates@jinja2 with their corresponding Genshi ones. Note that Genshi will **not** be supported concurrently with Jinja2. If for some reason you're stuck to having to support Genshi templates, you'll have to stick to Trac 1.2.x. But you really should make the transition effort as Jinja2 templates are 5-10x faster than their Genshi equivalent, for a 1/5th of the cost in memory usage. == Changes in the template syntax Most of the time, the porting is a straightforward operation. === expand a variable - Genshi [[xml($the_variable)]] - Jinja2 [[xml(${the_variable})]] Tip: {{{#!shell sed -ie 's,\$\([a-z_][a-z._]*\),${\1},g' template.html }}} === expand a simple computation - Genshi [[xml(${the_variable + 1})]] - Jinja2 [[xml(${the_variable + 1})]] However, Jinja2 expressions are only //similar// to Python expressions, there are a few differences and limitations, see [http://jinja.pocoo.org/docs/dev/templates/#expressions expressions] doc. See also [#setcomplexvariabels set complex variables] below for more involved examples. === include another template #include - Genshi [[xml()]] - Jinja2 [[xml(# include "the_file.html" ignore missing)]] See [http://jinja.pocoo.org/docs/dev/templates/#include include] doc. Note that the `ignore missing` part is mandatory no templates are given to the `include` directive. This includes the following situation: {{{#!html+jinja # include "sometemplate.html" if false }}} This alone would raise an error. The correct thing to write is: {{{#!html+jinja # include "sometemplate.html" if false ignore missing }}} It is also possible to pass "parameters" to included templates. Those are not actually declared parameters, simply variables expected to be available in the template that can be set for the scope of one specific include. This works exactly like in Genshi, with a with statement: - Genshi {{{#!html+genshi }}} - Jinja {{{#!html+jinja # with # set can_append = false # set preview_mode = false # include "jticket_box.html" # endwith }}} See [http://jinja.pocoo.org/docs/dev/extensions/#with-statement with] doc. In passing, note how the boolean constants slightly differ from Python, `False` becomes `false`, `True` becomes `true` and `None` is `none`. Caveat: contrary to the Genshi way, one shouldn't include the `"layout.html"` template in order to inherit the default page layout. There's a big difference in the way template "inheritance" works between Genshi and Jinja2, see HtmlTemplates#Jinjaarchitecture for all the details. Despite these differences, we kept the same spirit and there's actually also a `"layout.html"` template that you can "inherit" from (as well as a `"theme.html"` template that the layout inherits in turn). But instead of "including" it in your template, you "extend" it: {{{#!html+jinja # extends "layout.html" }}} But this is not the place to go further in the details about how extending works, refer to the [http://jinja.pocoo.org/docs/dev/templates/#extends extends] documentation and to the link above for how this applies to Trac. === simple if...then (no else) #if - Genshi [[xml(OK)]] or simply: [[xml(OK)]] - Jinja2 {{{#!html+jinja # if flag: OK # endif }}} See [http://jinja.pocoo.org/docs/dev/templates/#if if] doc. === if...then...else - Genshi {{{#!html+genshi OK !!! }}} or simply: {{{#!html+genshi OK !!! }}} - Jinja2 {{{#!html+jinja # if flag: OK # else: !!! # endif }}} If you really have to, you can also use the block style: {{{#!html+jinja {% if flag %}OK{% else %}!!!{% endif %} }}} However this goes against readability and processing via the [./Checker jinjachecker] tool, so we really advise that you stick to the use of //[http://jinja.pocoo.org/docs/dev/templates/#line-statements line statements]//. === iterate over a collection #for - Genshi {{{#!html+genshi }}} or simply: {{{#!html+genshi }}} - Jinja2 {{{ #!xml }}} See [http://jinja.pocoo.org/docs/dev/templates/#for for] doc. ==== No need for `enumerate` - Genshi: {{{#!html+genshi ${section.name} }}} - Jinja2: {{{#!html+jinja # for option in section.options: # if loop.first: ${section.name} }}} All common uses (and more) for such an `idx` variable are addressed by the special `loop` variable. See [http://jinja.pocoo.org/docs/dev/templates/#for loop] doc. === define a macro #macro - Genshi {{{#!html+genshi
$key
$val
 }}} - Jinja2 {{{#!html+jinja # macro entry(key, val='--')
${key}
${val}
# endmacro }}} See [http://jinja.pocoo.org/docs/dev/templates/#macros macros] doc. === set a variable - Genshi {{{#!html+genshi We have ${count > 10 and 'too much' or count} elements. }}} Note that we had to use `>` in Genshi, we can't use `>` directly. - Jinja2 {{{#!html+jinja # set count = len(collection) We have ${'too much' if count is greaterthan(10) else count} elements. }}} Note that we avoid using `>` in Jinja2 expressions as well, but simply to avoid that XML/HTML text editors get confused. We added a few custom tests for that (`greaterthan`, `greaterthanorequal`, `lessthan`, `lessthanorequal`). See [http://jinja.pocoo.org/docs/dev/templates/#tests tests] doc. === set HTML attributes #htmlattr In Genshi, an attribute with a `None` value wouldn't be output. However, Jinja2 doesn't know what an attribute is (or anything else about HTML, XML for that matter), so we have to use a special filter, `htmlattr`, to reproduce this behavior: - Genshi: {{{#!html+genshi }}} - Jinja2: {{{#!html+jinja # set components = plugin.modules|map(attribute='components')|flatten }}} (the `htmlattr` filter will add a space if needed; that way, if the condition is true, you end up with ``, otherwise with just ``) If you wonder why the `if all(...)` expression morphed into `if not components|...`, it's because Jinja2 expressions are similar to Python expressions, but not quite the same. === set complex variables #set Note that Jinja2 expressions are a subset of Python expressions, and for the sake of simplicity the generator expressions are not part of that subset. This limitation often requires one to make creative use of [http://jinja.pocoo.org/docs/dev/templates/#filters filters], [http://jinja.pocoo.org/docs/dev/templates/#builtin-filters built-in] or custom (`min`, `max`, `trim`, `flatten`). A few more examples: ||= Genshi ||= Jinja2 || || `${', '.join([p.name for p in faulty_plugins])}` || \ || `${faulty_plugins|map('name')|join(', ')}` || || `sum(1 for change in changes if 'cnum' in change)` || \ || `changes|selectattr('cnum')|list|count` || || `sum(1 for change in changes if 'cnum' not in change)` || \ || `changes|rejectattr('cnum')|list|count` || || ... || ... || === conditional wrappers There's no direct equivalent to the `py:strip`, but it can often be emulated with an `if/else/endif`. - Genshi {{{#!html+genshi $plugin.name }}} - Jinja2 {{{#!html+jinja # if url: ${plugin.name} # else: ${plugin.name} # endif }}} If the repeated content is complex, one can use a //block assignment// (see below). === i18n #trans Genshi had a pretty good notion of what was a piece of translatable text within an HTML template, but Jinja2 doesn't, so there's no "guessing" and no i18n will happen unless explicitly asked. This can be done in two ways. First, with translation expressions, using the familiar `_()` gettext function (`gettext` and `ngettext` also supported). - Genshi: [[xml(Trac detected an internal error:)]] - Jinja2: [[xml(${_("Trac detected an internal error:")})]] Second, using `trans` directives. - Genshi: {{{#!html+genshi

Otherwise, please ${create_ticket(tracker)} a new bug report describing the problem and explain how to reproduce it.

}}} - Jinja2: {{{#!html+jinja

# trans create = create_ticket(tracker) Otherwise, please ${create} a new bug report describing the problem and explain how to reproduce it. # endtrans

}}} See [http://jinja.pocoo.org/docs/dev/templates/#i18n i18n] doc. Note that only direct variable expansions are supported in `trans` blocks, nothing more complex. So one way to deal with complex translatable content is to factor out the complex parts in variable blocks. See [http://jinja.pocoo.org/docs/dev/templates/#block-assignments block assignments] doc. - Genshi: {{{#!html+genshi

There was an internal error in Trac. It is recommended that you notify your local Trac administrator with the information needed to reproduce the issue.

}}} - Jinja2: {{{#!html+jinja

# set trac_admin = _("Trac administrator") # set project_admin # if project.admin: ${trac_admin} # else: ${trac_admin} # endif # endset # trans project_admin = project_admin|safe There was an internal error in Trac. It is recommended that you notify your local ${project_admin} with the information needed to reproduce the issue. # endtrans

}}} (the need for the `|safe` filter in the above might go away once the following issue //[https://github.com/mitsuhiko/jinja2/issues/490 Should set blocks be safe by default]// gets fixed) Note that another tricky case is when you want to use `gettext` and one of the variables is Markup. Using `|safe` is also needed, but that's not enough, as currently `gettext()` doesn't support Markup, you need to use `tgettext()` which is available with the `tag_` shortcut: {{{#!html+jinja # set preferences_link ${ _("Preferences")} # endset ${tag_("Set your email in %(preferences_link)s", preferences_link=preferences_link|safe)} }}} == Examples === Standalone template Let's first take a simple full-contained example from the Trac source, the simple index.html / jindex.html templates. - Genshi [source:sandbox/genshi/templates/index.html@3728 index.html]: {{{#!html+genshi Available Projects

Available Projects

}}} - Jinja [source:cboos.git/trac/templates/jindex.html@jinja2 jindex.html]: {{{#!html+jinja ${_("Available Projects")}

${_("Available Projects")}

}}} In this small example, there's no common Trac layout used (as the index is a bit special). For how a "normal" template looks like, see for example [source:trac/templates/jdiff_form.html@jinja2 jdiff_form.html], another small template. Note that a Jinja2 .html template can usually be rendered directly in the browser, to have a rough taste of how it will look like: {{{#!div style="border: 2px solid #ccc; margin: 1em; padding: 0 2em" {{{#!html (html mode on purpose here!)

${_("Available Projects")}

}}} }}} Though there's absolutely no constraints on what text a Jinja2 template may contain, for templates that will produce HTML (or XML), it will be useful if the template is itself already '''a well-formed XML document'''. **Never** go back to the bad old habits from the ClearSilver time, were sometimes the logic in those templates took advantage of the lack of well-formedness constraints, e.g. by conditionally inserting end/start pairs of tags to split sequences. Such templates were hard to maintain, and you always have cleaner alternatives. The [./Checker jinjachecker] tool should also help you maintain well-formed templates by stripping off Jinja2 expressions and line statements before attempting to XML validate the document ([pypi:lxml] should be installed for this feature). === "Standard" templates By "standard", we mean templates that follow the standard Trac layout, and even adapt to the currently selected theme. Instead of the Genshi way of including a template containing filters, the Jinja2 way follows an "object oriented" approach, with inheritance and overriders. Consider that some named sections (or "blocks") of the base template are similar to "methods", imagine that you only have to "subclass" this base template and "reimplement" the overridable methods with your specific content, and there you have it. More specifically, you'll have to "extend" the [source:cboos.git/trac/templates/jlayout.html@jinja2 jlayout.html] template, and redefine the "head", and "content" blocks if needed. All the details are available in HtmlTemplates#Jinjaarchitecture, including a walkthrough for the specific example of the [source:cboos.git/trac/search/templates/jsearch.html@jinja2 jsearch.html] template. For the jsearch.html example we focus on the //structure// of the templates, the //include// relationship and the decomposition in //blocks//. But we also have a complete conversion [./Example example], which displays the Genshi wiki_view.html template and the Jinja2 jwiki_view.html template side-by-side, along with comments explaining the conversion choices. == Changes in the controllers == === Implementing the `IRequestHandler` interface With Genshi, the data for the template is basically a `dict`, which has to be returned by `process_request` at the same time as the template name. This hasn't changed with Jinja2. In fact, no changes to the `IRequestHandler` interface were needed. === Replacing the `ITemplateStreamFilter` interface #ReplacingITemplateStreamFilter One of the strengths of Genshi was its ability to transform the normal HTML content and, for example, to inject arbitrary content at any point in the HTML, thanks to the use of the Transform stream filter and its API. With Jinja2, the content is produced in one step, with no kind of post-processing. Hence the content should either be produced right away, or if it really has to be produced as an extra step, it should be produced dynamically on client-side using JavaScript. ==== Producing the correct content directly There were two post-processing steps from which plugin writers did benefit, possibly unknowingly: 1. the addition of the `__FORM_TOKEN` hidden parameter to
elements, necessary for successful POST operations 2. accessibility key enabling/disabling (TODO) As this no longer happen, it's now the responsibility of plugin writers to add this in their content. This is simple enough: {{{#!html+jinja ...
}}} This gets even simpler thanks to a default macro: {{{#!html+jinja
${jmacros.form_token_input()} ...
}}} The `jmacros` corresponds to the [source:cboos.git/trac/templates/jmacros.html@jinja2 trac/templates/jmacros.html] default macros, and this file is included by default (in `jlayout.html`), so you don't have to bother to include it yourself (as most of the templates will extend `jlayout.html`). ==== Hooking into the HTML content produced by other templates On this day, 127/898 plugins (14.1%) on trac-hacks.org make use of `filter_stream()` from the `ITemplateStreamFilter` interface. So this means this specific step of the migration, perhaps the less straightforward, will be of interest for most plugin developers. Note that though it wouldn't harm to leave the code for `ITemplateStreamFilter` around for use by Trac < 1.4, the new suggested way also works great with earlier versions of Trac (1.0 and 1.2, perhaps even 0.12), so there's really no reason to maintain both versions once you did the switch. The steps for replacing `filter_stream()` are the following: 1. implement `ITemplateProvider` if you haven't done so already, as you'll need to provide a JavaScript file 2. implement `IRequestFilter` if you haven't done so already, as you'll need to add the