Merge 023a646b0a24e0f37eaa308b793cc8eecfb1ba57 into ecee73eafd694bb91b840882aea5b3d6c5b40a7b

docs/dev/plugins/rerank.rst

@@ -0,0 +1,9 @@
+.. _rerank plugin:
+
+================
+Rerank
+================
+
+.. automodule:: searx.plugins.rerank
+  :members:
+

searx/plugins/_core.py

@@ -68,6 +68,9 @@ class PluginInfo:
     keywords: list[str] = field(default_factory=list)
     """See :py:obj:`Plugin.keywords`"""
 
+    is_allowed: bool = True
+    """Switch to disable plugin completely, without the user preference."""
+
 
 class Plugin(abc.ABC):
     """Abstract base class of all Plugins."""

searx/plugins/rerank.py

@@ -0,0 +1,115 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# pylint: disable=missing-module-docstring, missing-class-docstring
+from __future__ import annotations
+import typing
+
+from flask_babel import gettext
+
+from searx import settings
+from searx.plugins import Plugin, PluginInfo
+from searx.result_types import EngineResults
+
+if typing.TYPE_CHECKING:
+    from searx.search import SearchWithPlugins
+    from searx.extended_types import SXNG_Request
+
+try:
+    import bm25s
+except ImportError:
+    # Import error is ignored because the admin has to install bm25s manually to use the plugin
+    bm25s = None
+
+
+class SXNGPlugin(Plugin):
+    """Plugin which reranks the search results using the Okapi BM25 algorithm.
+
+    This plugin utilizes the `bm25s` library to reorder search results based on their relevance to the search query,
+    potentially improving the quality of results.  Before enabling this plugin,
+    ensure you have installed the ``bm25s`` pip package.  e.g. by installing it directly via pip or
+    by adding it to the project's `requirements.txt` file.
+
+    Configuration:
+    --------------
+    To enable the Rerank plugin, add it to the `enabled_plugins` list in your `settings.yml` file:
+
+    .. code:: yaml
+
+    enabled_plugins:
+        ..
+        - 'Rerank plugin'
+
+    By default, the plugin retains the information about which engines found a particular result.
+    Results that appear in multiple engine results will receive a score boost.
+    This approach might be relevant if you wish results found by different engines to be prioritized.
+    You can modify this behaviour by configuring the ``remove_extra_engines`` setting.
+    If ``remove_extra_engines`` is set to ``true``, the original engine list is reduced to only the first engine.
+    This is useful when you prefer the reranking to not be affected by any potential overlap
+    of results from different engines.
+
+    .. code:: yaml
+
+    rerank:
+        remove_extra_engines: true
+
+    """
+
+    id = "rerank"
+    default_on = False
+
+    def __init__(self):
+        super().__init__()
+
+        self.stopword_langs = ['en', 'de', 'nl', 'fr', 'es', 'pt', 'it', 'ru', 'sv', 'no', 'zh']
+        self.remove_extra_engines = settings.get('rerank', {}).get('remove_extra_engines')
+
+        self.info = PluginInfo(
+            id=self.id,
+            name=gettext("Rerank plugin"),
+            description=gettext("""Rerank search results, ignoring original engine ranking"""),
+            preference_section="general",
+            is_allowed=bm25s is not None,
+        )
+
+    def post_search(self, request: "SXNG_Request", search: "SearchWithPlugins") -> EngineResults:
+        results = EngineResults()
+
+        if not bm25s:
+            return results
+
+        # pylint: disable=protected-access
+        results = search.result_container._merged_results
+        query = search.search_query.query
+        locale = search.search_query.locale
+
+        # Determine the stopwords based on the selected locale
+        stopwords = locale.language if locale and locale.language in self.stopword_langs else 'en'
+
+        retriever = bm25s.BM25()
+        result_tokens = bm25s.tokenize(
+            [
+                f"{result.get('title', '')} | {result.get('content', '')} | {result.get('url', '')}"
+                for result in results
+            ],
+            stopwords=stopwords,
+        )
+        retriever.index(result_tokens)
+
+        query_tokens = bm25s.tokenize(query, stopwords=stopwords)
+
+        # Retrieve ranked indices of results based on the query tokens
+        indices = retriever.retrieve(query_tokens, k=len(results), return_as='documents', show_progress=False)
+
+        if self.remove_extra_engines:
+            # Only keep the main engine and set our ranking
+            for position, index in enumerate(indices[0]):
+                if 'positions' in results[index]:
+                    results[index]['positions'] = [position + 1]
+                    results[index]['engines'] = set([results[index]['engine']])
+        else:
+            # Overwrite all engine positions with the new ranking
+            # Results returned from multiple engines will still get a score boost
+            for position, index in enumerate(indices[0]):
+                if 'positions' in results[index]:
+                    results[index]['positions'] = [position + 1] * len(results[index]['positions'])
+
+        return results

searx/settings.yml

@@ -249,6 +249,7 @@ outgoing:
 #   - 'Hostnames plugin'  # see 'hostnames' configuration below
 #   - 'Open Access DOI rewrite'
 #   - 'Tor check plugin'
+#   - 'Rerank plugin'  # requires the bm25s python dependency to be installed
 
 # Configuration of the "Hostnames plugin":
 #

searx/templates/simple/preferences.html

@@ -38,7 +38,7 @@
 
 {%- macro plugin_preferences(section) -%}
   {%- for plugin in plugins_storage -%}
-    {%- if plugin.preference_section == section -%}
+    {%- if plugin.preference_section == section and plugin.is_allowed -%}
       <fieldset>{{- '' -}}
 	<legend>{{ _(plugin.name) }}</legend>{{- '' -}}
 	<div class="value">