[refactor] migrate plugins from "module" to class SXNGPlugin

This patch brings two major changes:

- ``Result.filter_urls(..)`` to pass a filter function for URL fields
- The ``enabled_plugins:`` section in SearXNG's settings do no longer exists.

To understand plugin development compile documentation:

    $ make docs.clean docs.live

and read http://0.0.0.0:8000/dev/plugins/development.html

There is no longer a distinction between built-in and external plugin, all
plugins are registered via the settings in the ``plugins:`` section.

In SearXNG, plugins can be registered via a fully qualified class name.  A
configuration (`PluginCfg`) can be transferred to the plugin, e.g. to activate
it by default / *opt-in* or *opt-out* from user's point of view.

built-in plugins
================

The built-in plugins are all located in the namespace `searx.plugins`.

.. code:: yaml

    plugins:

      searx.plugins.calculator.SXNGPlugin:
        active: true

      searx.plugins.hash_plugin.SXNGPlugin:
        active: true

      searx.plugins.self_info.SXNGPlugin:
        active: true

      searx.plugins.tracker_url_remover.SXNGPlugin:
        active: true

      searx.plugins.unit_converter.SXNGPlugin:
        active: true

      searx.plugins.ahmia_filter.SXNGPlugin:
        active: true

      searx.plugins.hostnames.SXNGPlugin:
        active: true

      searx.plugins.oa_doi_rewrite.SXNGPlugin:
        active: false

      searx.plugins.tor_check.SXNGPlugin:
        active: false

external plugins
================

SearXNG supports *external plugins* / there is no need to install one, SearXNG
runs out of the box.

- Only show green hosted results: https://github.com/return42/tgwf-searx-plugins/

To get a developer installation in a SearXNG developer environment:

.. code:: sh

   $ git clone git@github.com:return42/tgwf-searx-plugins.git
   $ ./manage pyenv.cmd python -m \
         pip install -e tgwf-searx-plugins

To register the plugin in SearXNG add ``only_show_green_results.SXNGPlugin`` to
the ``plugins:``:

.. code:: yaml

    plugins:
      # ...
      only_show_green_results.SXNGPlugin:
        active: false

Result.filter_urls(..)
======================

The ``Result.filter_urls(..)`` can be used to filter and/or modify URL fields.
In the following example, the filter function ``my_url_filter``:

.. code:: python

   def my_url_filter(result, field_name, url_src) -> bool | str:
       if "google" in url_src:
           return False              # remove URL field from result
       if "facebook" in url_src:
           new_url = url_src.replace("facebook", "fb-dummy")
           return new_url            # return modified URL
       return True                   # leave URL in field unchanged

is applied to all URL fields in the :py:obj:`Plugin.on_result` hook:

.. code:: python

   class MyUrlFilter(Plugin):
       ...
       def on_result(self, request, search, result) -> bool:
           result.filter_urls(my_url_filter)
           return True

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

5 files changed, 41 insertions, 13 deletions

diff --git a/tests/unit/settings/user_settings.yml b/tests/unit/settings/user_settings.yml
index c582e4652..fc80173f6 100644
--- a/tests/unit/settings/user_settings.yml
+++ b/tests/unit/settings/user_settings.yml
@@ -32,6 +32,36 @@ ui:
   theme_args:
     simple_style: auto
 
+plugins:
+
+  searx.plugins.calculator.SXNGPlugin:
+    active: true
+
+  searx.plugins.hash_plugin.SXNGPlugin:
+    active: true
+
+  searx.plugins.self_info.SXNGPlugin:
+    active: true
+
+  searx.plugins.tracker_url_remover.SXNGPlugin:
+    active: true
+
+  searx.plugins.unit_converter.SXNGPlugin:
+    active: true
+
+  searx.plugins.ahmia_filter.SXNGPlugin:
+    active: true
+
+  searx.plugins.hostnames.SXNGPlugin:
+    active: true
+
+  searx.plugins.oa_doi_rewrite.SXNGPlugin:
+    active: false
+
+  searx.plugins.tor_check.SXNGPlugin:
+    active: false
+
+
 engines:
   - name: wikidata
     engine: wikidata
diff --git a/tests/unit/test_plugin_calculator.py b/tests/unit/test_plugin_calculator.py
index ec0258cab..505812e19 100644
--- a/tests/unit/test_plugin_calculator.py
+++ b/tests/unit/test_plugin_calculator.py
@@ -7,9 +7,7 @@ import searx.plugins
 import searx.preferences
 
 from searx.extended_types import sxng_request
-from searx.plugins._core import _default, ModulePlugin
 from searx.result_types import Answer
-from searx.utils import load_module
 
 from tests import SearxTestCase
 from .test_utils import random_string
@@ -20,13 +18,10 @@ class PluginCalculator(SearxTestCase):
 
     def setUp(self):
         super().setUp()
-
-        f = _default / "calculator.py"
-        mod = load_module(f.name, str(f.parent))
         engines = {}
 
         self.storage = searx.plugins.PluginStorage()
-        self.storage.register(ModulePlugin(mod, "searx.plugins.calculator"))
+        self.storage.load_settings({"searx.plugins.calculator.SXNGPlugin": {"active": True}})
         self.storage.init(self.app)
         self.pref = searx.preferences.Preferences(["simple"], ["general"], engines, self.storage)
         self.pref.parse_dict({"locale": "en"})
diff --git a/tests/unit/test_plugin_hash.py b/tests/unit/test_plugin_hash.py
index 7854763bc..0c87869d1 100644
--- a/tests/unit/test_plugin_hash.py
+++ b/tests/unit/test_plugin_hash.py
@@ -39,7 +39,7 @@ class PluginHashTest(SearxTestCase):
         engines = {}
 
         self.storage = searx.plugins.PluginStorage()
-        self.storage.register_by_fqn("searx.plugins.hash_plugin.SXNGPlugin")
+        self.storage.load_settings({"searx.plugins.hash_plugin.SXNGPlugin": {"active": True}})
         self.storage.init(self.app)
         self.pref = searx.preferences.Preferences(["simple"], ["general"], engines, self.storage)
         self.pref.parse_dict({"locale": "en"})
diff --git a/tests/unit/test_plugin_self_info.py b/tests/unit/test_plugin_self_info.py
index 3ff18464b..4a2e6c416 100644
--- a/tests/unit/test_plugin_self_info.py
+++ b/tests/unit/test_plugin_self_info.py
@@ -21,12 +21,14 @@ class PluginIPSelfInfo(SearxTestCase):
 
     def setUp(self):
         super().setUp()
+        engines = {}
 
         self.storage = searx.plugins.PluginStorage()
-        self.storage.register_by_fqn("searx.plugins.self_info.SXNGPlugin")
+        self.storage.load_settings({"searx.plugins.self_info.SXNGPlugin": {"active": True}})
         self.storage.init(self.app)
-        self.pref = searx.preferences.Preferences(["simple"], ["general"], {}, self.storage)
+        self.pref = searx.preferences.Preferences(["simple"], ["general"], engines, self.storage)
         self.pref.parse_dict({"locale": "en"})
+
         cfg = searx.limiter.get_cfg()
         searx.botdetection.init(cfg, None)
 
diff --git a/tests/unit/test_plugins.py b/tests/unit/test_plugins.py
index 33df0f320..cf23bf27e 100644
--- a/tests/unit/test_plugins.py
+++ b/tests/unit/test_plugins.py
@@ -4,6 +4,7 @@
 import babel
 from mock import Mock
 
+import searx
 import searx.plugins
 import searx.preferences
 import searx.results
@@ -14,7 +15,7 @@ from searx.extended_types import sxng_request
 from tests import SearxTestCase
 
 plg_store = searx.plugins.PluginStorage()
-plg_store.load_builtins()
+plg_store.load_settings(searx.get_setting("plugins"))
 
 
 def get_search_mock(query, **kwargs):
@@ -47,11 +48,11 @@ def do_post_search(query, storage, **kwargs) -> Mock:
 
 class PluginMock(searx.plugins.Plugin):
 
-    def __init__(self, _id: str, name: str, default_on: bool):
+    def __init__(self, _id: str, name: str, active: bool):
+        plg_cfg = searx.plugins.PluginCfg(active=active)
         self.id = _id
-        self.default_on = default_on
         self._name = name
-        super().__init__()
+        super().__init__(plg_cfg)
 
     # pylint: disable= unused-argument
     def pre_search(self, request, search) -> bool: