ikiwiki/doc/plugins/po.mdwn

[[!template id=plugin name=po core=0 author="[[intrigeri]]"]]
[[!tag type/format]]

This plugin adds support for multi-lingual wikis, translated with
gettext, using [po4a](http://po4a.alioth.debian.org/).

It depends on the Perl `Locale::Po4a::Po` library (`apt-get install po4a`).
As detailed bellow in the security section, `po4a` is subject to
denial-of-service attacks before version 0.35.

[[!toc levels=2]]

Introduction
============

A language is chosen as the "master" one, and any other supported
language is a "slave" one.

A page written in the "master" language is a "master" page. It can be
of any page type supported by ikiwiki, except `po`. It does not have to be
named a special way: migration to this plugin does not imply any page
renaming work.

Example: `bla/page.mdwn` is a "master" Markdown page written in
English; if `usedirs` is enabled, it is rendered as
`bla/page/index.en.html`, else as `bla/page.en.html`.

Any translation of a "master" page into a "slave" language is called
a "slave" page; it is written in the gettext PO format. `po` is now
a page type supported by ikiwiki.

Example: `bla/page.fr.po` is the PO "message catalog" used to
translate `bla/page.mdwn` into French; if `usedirs` is enabled, it is
rendered as `bla/page/index.fr.html`, else as `bla/page.fr.html`

(In)Compatibility
=================

This plugin does not support the `indexpages` mode. If you don't know
what it is, you probably don't care.


Configuration
=============

Supported languages
-------------------

`po_master_language` is used to set the "master" language in
`ikiwiki.setup`, such as:

        po_master_language => { 'code' => 'en', 'name' => 'English' }

`po_slave_languages` is used to set the list of supported "slave"
languages, such as:

        po_slave_languages => { 'fr' => 'Français',
                                'es' => 'Castellano',
                                'de' => 'Deutsch',
        }

Decide which pages are translatable
-----------------------------------

The `po_translatable_pages` setting configures what pages are
translatable. It is a [[ikiwiki/PageSpec]], so you have lots of
control over what kind of pages are translatable.

The `.po` files are not considered as being translatable, so you don't need to
worry about excluding them explicitly from this [[ikiwiki/PageSpec]].

Internal links
--------------

### Links targets

The `po_link_to` option in `ikiwiki.setup` is used to decide how
internal links should be generated, depending on web server features
and site-specific preferences.

#### Default linking behavior

If `po_link_to` is unset, or set to `default`, ikiwiki's default
linking behavior is preserved: `\[[destpage]]` links to the master
language's page.

#### Link to current language

If `po_link_to` is set to `current`, `\[[destpage]]` links to the
`destpage`'s version written in the current page's language, if
available, *i.e.*:

* `foo/destpage/index.LL.html` if `usedirs` is enabled
* `foo/destpage.LL.html` if `usedirs` is disabled

#### Link to negotiated language

If `po_link_to` is set to `negotiated`, `\[[page]]` links to the
negotiated preferred language, *i.e.* `foo/page/`.

(In)compatibility notes:

* if `usedirs` is disabled, it does not make sense to set `po_link_to`
  to `negotiated`; this option combination is neither implemented
  nor allowed.
* if the web server does not support Content Negotiation, setting
  `po_link_to` to `negotiated` will produce a unusable website.

### Links appearance

When `po_translation_status_in_links` is enabled, the text of a link
to a slave pages displays this page's translation status.

When the `po_strictly_refresh_backlinks` setting is enabled, a page is
refreshed every time a backlinked page is changed. This updates the
translation status in links, and helps having a consistent translated
wiki. Beware, this make every page depend on every page that links to
it, which can slow everything down and bloat the dependency pagespecs.

Server support
==============

Apache
------

Using Apache `mod_negotiation` makes it really easy to have Apache
serve any page in the client's preferred language, if available.
This is the default Debian Apache configuration.

When `usedirs` is enabled, one has to set `DirectoryIndex index` for
the wiki context.

Setting `DefaultLanguage LL` (replace `LL` with your default MIME
language code) for the wiki context can help to ensure
`bla/page/index.en.html` is served as `Content-Language: LL`.

lighttpd
--------

lighttpd unfortunately does not support content negotiation.

**FIXME**: does `mod_magnet` provide the functionality needed to
 emulate this?


Usage
=====

Templates
---------

When `po_link_to` is not set to `negotiated`, one should replace some
occurrences of `BASEURL` with `HOMEPAGEURL` to get correct links to
the wiki homepage.

The `ISTRANSLATION` and `ISTRANSLATABLE` variables can be used to
display things only on translatable or translation pages.

### Display page's versions in other languages

The `OTHERLANGUAGES` loop provides ways to display other languages'
versions of the same page, and the translations' status.

One typically adds the following code to `templates/page.tmpl`:

	<TMPL_IF NAME="OTHERLANGUAGES">
	<div id="otherlanguages">
	  <ul>
	  <TMPL_LOOP NAME="OTHERLANGUAGES">
	    <li>
	      <a href="<TMPL_VAR NAME="URL">"><TMPL_VAR NAME="LANGUAGE"></a>
	      <TMPL_UNLESS NAME="MASTER">
	        (<TMPL_VAR NAME="PERCENT">&nbsp;%)
	      </TMPL_UNLESS>
	    </li>
	  </TMPL_LOOP>
	  </ul>
	</div>
	</TMPL_IF>

The following variables are available inside the loop (for every page in):

* `URL` - url to the page
* `CODE` - two-letters language code
* `LANGUAGE` - language name (as defined in `po_slave_languages`)
* `MASTER` - is true (1) if, and only if the page is a "master" page
* `PERCENT` - for "slave" pages, is set to the translation completeness, in percents

### Display the current translation status

The `PERCENTTRANSLATED` variable is set to the translation
completeness, expressed in percent, on "slave" pages.

One can use it this way:

	<TMPL_IF NAME="ISTRANSLATION">
	<div id="percenttranslated">
	  <TMPL_VAR NAME="PERCENTTRANSLATED">
	</div>
	</TMPL_IF>

Additional PageSpec tests
-------------------------

This plugin enhances the regular [[ikiwiki/PageSpec]] syntax with some
additional tests that are documented [[here|ikiwiki/pagespec/po]].

Automatic PO file update
------------------------

Committing changes to a "master" page:

1. updates the POT file and the PO files for the "slave" languages;
   the updated PO files are then put under version control;
2. triggers a refresh of the corresponding HTML slave pages.

Also, when the plugin has just been enabled, or when a page has just
been declared as being translatable, the needed POT and PO files are
created, and the PO files are checked into version control.

Discussion pages and other sub-pages
------------------------------------

Discussion should happen in the language in which the pages are
written for real, *i.e.* the "master" one. If discussion pages are
enabled, "slave" pages therefore link to the "master" page's
discussion page.

Likewise, "slave" pages are not supposed to have sub-pages;
[[WikiLinks|wikilink]] that appear on a "slave" page therefore link to
the master page's sub-pages.

Translating
-----------

One can edit the PO files using ikiwiki's CGI (a message-by-message
interface could also be implemented at some point).

If [[tips/untrusted_git_push]] is setup, one can edit the PO files in one's
preferred `$EDITOR`, without needing to be online.

Markup languages support
------------------------

Markdown is well supported. Some other markup languages supported by
ikiwiki mostly work, but some pieces of syntax are not rendered
correctly on the slave pages:

* [[reStructuredText|rst]]: anonymous hyperlinks and internal
  cross-references
* [[wikitext]]: conversion of newlines to paragraphs
* [[creole]]: verbatim text is wrapped, tables are broken
* [[html]] and LaTeX: not supported yet; the dedicated po4a modules
  could be used to support them, but they would need a security audit
* other markup languages have not been tested.

Security
========

[[./security]] contains a detailed security analysis of this plugin
and its dependencies.

When using po4a older than 0.35, it is recommended to uninstall
`Text::WrapI18N` (Debian package `libtext-wrapi18n-perl`), in order to
avoid a potential denial of service.

TODO
====

Better links
------------

### Page title in links

Using the fix to
[[bugs/pagetitle_function_does_not_respect_meta_titles]] from
[[intrigeri]]'s `meta` branch, the generated links' text is based on
the page titles set with the [[meta|plugins/meta]] plugin. This has to
be merged into ikiwiki upstream, though.

Robustness tests
----------------

### Enabling/disabling the plugin

* enabling the plugin with `po_translatable_pages` set to blacklist: **OK**
* enabling the plugin with `po_translatable_pages` set to whitelist: **OK**
* enabling the plugin without `po_translatable_pages` set: **OK**
* disabling the plugin: **OK**

### Changing the plugin config

* adding existing pages to `po_translatable_pages`: **OK**
* removing existing pages from `po_translatable_pages`: **OK**
* adding a language to `po_slave_languages`: **OK**
* removing a language from `po_slave_languages`: **OK**
* changing `po_master_language`: **OK**
* replacing `po_master_language` with a language previously part of
  `po_slave_languages`: needs two rebuilds, but **OK** (this is quite
  a perverse test actually)

### Creating/deleting/renaming pages

All cases of master/slave page creation/deletion/rename, both via RCS
and via CGI, have been tested.

### Misc

* general test with `usedirs` disabled: **OK**
* general test with `indexpages` enabled: **not OK**
* general test with `po_link_to=default` with `userdirs` enabled: **OK**
* general test with `po_link_to=default` with `userdirs` disabled: **OK**

Misc. bugs
----------

Documentation
-------------

Maybe write separate documentation depending on the people it targets:
translators, wiki administrators, hackers. This plugin may be complex
enough to deserve this.