[fix] plugin JS/CSS dependencies depend on themes

SearXNG supports plugins. Plugins can declare JavaScript and CSS
dependencies. Currently three plugins declare such dependencies:

* search_on_category_select (on by default)
* vim_hotkeys
* infinite_scroll

If a user enables a plugin its JavaScript and CSS dependencies are
embedded into every page. Sounds simple right?

Ironically in the Simple theme things start to get complicated:
The scripts were originally written for the Oscar theme and thus depend
on jQuery (which isn't loaded in the Simple theme) and look for certain
element identifiers (which aren't present in the Simple theme).  So how
did the plugins actually work with the simple theme?

The simple theme just didn't embed the plugin dependencies (which wasn't
even documented anywhere). Instead the simple theme checked if the paths
contained a certain script path, then set an attribute, which 00_init.js
detected and turned into a boolean, which was then used to enable
vanilla-JS reimplementations of the plugins.

This commit ends this horrible hack (and fixes #769).  The necessary
changes to the Simple theme are introduced in the next commit.

docs/dev/plugins.rst

@@ -15,12 +15,14 @@ Example plugin
 
 .. code:: python
 
+   from . import Resource
+
    name = 'Example plugin'
    description = 'This plugin extends the suggestions with the word "example"'
    default_on = False  # disabled by default
 
-   js_dependencies = tuple()  # optional, list of static js files
-   css_dependencies = tuple()  # optional, list of static css files
+   js_dependencies = tuple()  # optional, list of static js resources
+   css_dependencies = tuple()  # optional, list of static css resources
 
 
    # attach callback to the post search hook

searx/plugins/__init__.py

@@ -10,7 +10,7 @@ from os.path import abspath, basename, dirname, exists, join
 from shutil import copyfile
 from pkgutil import iter_modules
 from logging import getLogger
-from typing import List, Tuple
+from typing import List, Tuple, NamedTuple
 
 from searx import logger, settings
 
@@ -22,11 +22,18 @@ class Plugin:  # pylint: disable=too-few-public-methods
     name: str
     description: str
     default_on: bool
-    js_dependencies: Tuple[str]
-    css_dependencies: Tuple[str]
+    js_dependencies: Tuple['Resource']
+    css_dependencies: Tuple['Resource']
     preference_section: str
 
 
+class Resource(NamedTuple):
+    path: str
+    """ The path to the file """
+    themes: Tuple[str]
+    """ For which themes the file should be loaded """
+
+
 logger = logger.getChild("plugins")
 
 required_attrs = (

searx/plugins/infinite_scroll.py

@@ -1,9 +1,10 @@
 from flask_babel import gettext
+from . import Resource
 
 name = gettext('Infinite scroll')
 description = gettext('Automatically load next page when scrolling to bottom of current page')
 default_on = False
 preference_section = 'ui'
 
-js_dependencies = ('plugins/js/infinite_scroll.js',)
-css_dependencies = ('plugins/css/infinite_scroll.css',)
+js_dependencies = (Resource(path='plugins/js/infinite_scroll.js', themes=('oscar',)),)
+css_dependencies = (Resource(path='plugins/css/infinite_scroll.css', themes=('oscar',)),)

searx/plugins/search_on_category_select.py

@@ -15,6 +15,7 @@ along with searx. If not, see < http://www.gnu.org/licenses/ >.
 (C) 2015 by Adam Tauber, <asciimoo@gmail.com>
 '''
 from flask_babel import gettext
+from . import Resource
 
 name = gettext('Search on category select')
 description = gettext(
@@ -23,4 +24,6 @@ description = gettext(
 default_on = True
 preference_section = 'ui'
 
-js_dependencies = ('plugins/js/search_on_category_select.js',)
+js_dependencies = (
+    Resource(path='plugins/js/search_on_category_select.js', themes=('oscar',)),
+)

searx/plugins/vim_hotkeys.py

@@ -1,4 +1,5 @@
 from flask_babel import gettext
+from . import Resource
 
 name = gettext('Vim-like hotkeys')
 description = gettext(
@@ -9,5 +10,7 @@ description = gettext(
 default_on = False
 preference_section = 'ui'
 
-js_dependencies = ('plugins/js/vim_hotkeys.js',)
-css_dependencies = ('plugins/css/vim_hotkeys.css',)
+js_dependencies = (
+    Resource(path='plugins/js/vim_hotkeys.js', themes=('oscar',)),
+)
+css_dependencies = (Resource(path='plugins/css/vim_hotkeys.css', themes=('oscar',)),)

searx/templates/simple/base.html

@@ -17,6 +17,9 @@
   {% else %}
   <link rel="stylesheet" href="{{ url_for('static', filename='css/searxng.min.css') }}" type="text/css" media="screen" />
   {% endif %}
+  {%- for css in styles %}
+      <link rel="stylesheet" href="{{ url_for('static', filename=css) }}" type="text/css" />
+  {% endfor %}
   {% block styles %}{% endblock %}
   <script src="{{ url_for('static', filename='js/searxng.head.min.js') }}"
           data-method="{{ method or 'POST' }}"
@@ -59,5 +62,8 @@
     </p>
   </footer>
   <script src="{{ url_for('static', filename='js/searxng.min.js') }}"></script>
+  {% for script in scripts %}
+    <script src="{{ url_for('static', filename=script) }}"></script>
+  {% endfor %}
 </body>
 </html>

searx/webapp.py

@@ -456,7 +456,7 @@ def render(template_name: str, override_theme: str = None, **kwargs):
     kwargs['advanced_search'] = request.preferences.get_value('advanced_search')
     kwargs['query_in_title'] = request.preferences.get_value('query_in_title')
     kwargs['safesearch'] = str(request.preferences.get_value('safesearch'))
-    kwargs['theme'] = get_current_theme_name(override=override_theme)
+    kwargs['theme'] = current_theme = get_current_theme_name(override=override_theme)
     kwargs['categories_as_tabs'] = list(settings['categories_as_tabs'].keys())
     kwargs['categories'] = _get_enable_categories(categories.keys())
     kwargs['OTHER_CATEGORY'] = OTHER_CATEGORY
@@ -497,13 +497,15 @@ def render(template_name: str, override_theme: str = None, **kwargs):
     kwargs['scripts'] = set()
     for plugin in request.user_plugins:
         for script in plugin.js_dependencies:
-            kwargs['scripts'].add(script)
+            if current_theme in script.themes:
+                kwargs['scripts'].add(script.path)
 
     # styles from plugins
     kwargs['styles'] = set()
     for plugin in request.user_plugins:
         for css in plugin.css_dependencies:
-            kwargs['styles'].add(css)
+            if current_theme in css.themes:
+                kwargs['styles'].add(css.path)
 
     start_time = default_timer()
     result = render_template('{}/{}'.format(kwargs['theme'], template_name), **kwargs)