use jinja i18n infrastructure

To avoid duplication, this commit adds support for the jinja i18n extension, allowing the translation of message from templates. This also allows pybabel to extract messages with their correct source location, something not possible before. This makes merging of new and old messages more robust.
numericube · Apr 14, 2018 · 5895539 · 5895539
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diff --git a/README.md b/README.md
@@ -4,13 +4,13 @@ This plugin enables a smarter way to translate a [Lektor](http://getlektor.com)
 
 ## Principles
 
-The idea of this plugin is to capture the **sentences** from your **content**, and populate a standard *Gettext* [PO file](https://www.gnu.org/software/gettext/manual/html_node/PO-Files.html). Using usual tools, user can translate these files, very easily. Then the plugin will merge the translations into new [_alternative_](https://www.getlektor.com/docs/content/alts/) content files, providing a translated website.
+The idea of this plugin is to capture the **sentences** or **paragraphs** from your **content** and **templates**, and populate a standard *Gettext* [PO file](https://www.gnu.org/software/gettext/manual/html_node/PO-Files.html). Using usual tools, user can translate these files, very easily. Then the plugin will merge the translations into new [_alternative_](https://www.getlektor.com/docs/content/alts/) content files, providing a translated website.
 
 ## Configuration
 
 ### Configuration file
 
-`configs/i18n.ini`:
+#### `configs/i18n.ini`
 
     content = en
     translations = fr,es,it
@@ -24,9 +24,18 @@ Where :
 * `i18npath` is the directory where translation files will be produced/stored (default is `i18n`). This directory needs to be relative to root path.
 * `translate_paragraphwise` specifies whether translation strings are created per line or per paragraph. The latter is helpful for documents wrapping texts at 80 character boundaries. It is set to `False` by default.
 
+#### `babel.cfg`
+
+If you plan to localise your templates as well, you can use
+`{{ _("some string") }}` in your templates. To make this work, pybabel should be installed (pip install pybabel; maybe pip3). A `babel.cfg` also has to exist in your project root with this content:
+
+    [jinja2: **/templates/**.html]
+    encoding = utf-8
+    extensions=jinja2.ext.autoescape,jinja2.ext.with_
+
 ### Translatable fields
 
-In order for a field to be marked a translatable, an option has to be set in the field definition. Both blocks and flowblocks fields are subjects to translations.
+In order for a field to be marked as translatable, an option has to be set in the field definition. Both blocks and flowblocks fields are subjects to translations.
 
 in `flowblocks/*.ini` and/or `models/*.ini`, mark a field as translatable with :
 

diff --git a/lektor_i18n.py b/lektor_i18n.py
@@ -66,6 +66,34 @@ def trans(translator, s):
 def truncate(s, length=32):
     return (s[:length] + '..') if len(s) > length else s
 
+#pylint: disable=too-few-public-methods,redefined-variable-type
+class TemplateTranslator():
+    def __init__(self, i18npath):
+        self.i18npath = i18npath
+        self.__lastlang = None
+        self.translator = None
+        self.init_translator()
+
+    def init_translator(self):
+        ctx = get_ctx()
+        if not ctx:
+            self.translator = gettext.GNUTranslations()
+            return super().__init__()
+        if not self.__lastlang == ctx.locale:
+            self.__lastlang = ctx.locale
+            self.translator = gettext.translation("contents",
+                    join(self.i18npath, '_compiled'),
+                    languages=[ctx.locale], fallback=True)
+
+    def gettext(self, x):
+        self.init_translator() # lagnuage could have changed
+        return self.translator.gettext(x)
+
+    def ngettext(self, *x):
+        self.init_translator()
+        return self.translator.ngettext(*x)
+
+
 class Translations():
     """Memory of translations"""
 
@@ -195,20 +223,7 @@ class I18NPlugin(Plugin):
     name = u'i18n'
     description = u'Internationalisation helper'
 
-    def translate_tag(self, s, *args, **kwargs):
-        if not self.enabled:
-            return s # no operation
-        s = s.strip()
-        ctx = get_ctx()
-        if self.content_language==ctx.locale:
-            translations.add(s,'(dynamic)')
-            reporter.report_debug_info('added to translation memory (dynamic): ', truncate(s))
-            return s
-        else:
-            translator = gettext.translation("contents", join(self.i18npath,'_compiled'), languages=[ctx.locale], fallback = True)
-            return trans(translator, s)
-
-
+    # ToDo: what is this function for
     def choose_language(self, l, language, fallback='en', attribute='language'):
         """Will return from list 'l' the element with attribute 'attribute' set to given 'language'.
         If none is found, will try to return element with attribute 'attribute' set to given 'fallback'.
@@ -238,16 +253,18 @@ def on_setup_env(self):
         self.trans_parwise = self.get_config().get('translate_paragraphwise',
                 'false') in ('true','True','1')
         self.content_language=self.get_config().get('content', 'en')
+        self.env.jinja_env.add_extension('jinja2.ext.i18n')
+        self.env.jinja_env.policies['ext.i18n.trimmed'] = True # do a .strip()
+        self.env.jinja_env.install_gettext_translations(TemplateTranslator(self.i18npath))
+        # ToDo: is this stil required
         try:
             self.translations_languages=self.get_config().get('translations').replace(' ','').split(',')
         except AttributeError:
             raise RuntimeError('Please specify the "translations" configuration option in configs/i18n.ini')
 
         if not self.content_language in self.translations_languages:
             self.translations_languages.append(self.content_language)
-        self.env.jinja_env.filters['translate'] = self.translate_tag
-        self.env.jinja_env.globals['_'] = self.translate_tag
-        self.env.jinja_env.globals['choose_language'] = self.choose_language
+        #self.env.jinja_env.globals['choose_language'] = self.choose_language
 
     def process_node(self, fields, sections, source, zone, root_path):
         """For a give node (), identify all fields to translate, and add new