[refactor] hostnames plugin: add fallback for old hostname_replace plugin

Co-authored-by: Markus Heiser <markus.heiser@darmarit.de>

searx/plugins/hostname_replace.py

@@ -0,0 +1,35 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# pylint: disable=missing-module-docstring
+
+from flask_babel import gettext
+from searx.plugins import logger
+
+name = gettext('Hostname replace')
+description = "Deprecated / contact system admin to configure 'Hostnames plugin'!!"
+default_on = False
+preference_section = 'general'
+
+plugin_id = 'hostname_replace'
+logger = logger.getChild(plugin_id)
+
+REPORTED = False
+
+
+def deprecated_msg():
+    global REPORTED  # pylint: disable=global-statement
+    if REPORTED:
+        return
+    logger.error(
+        "'Hostname replace' plugin is deprecated and will be dropped soon!"
+        " Configure 'Hostnames plugin':"
+        " https://docs.searxng.org/src/searx.plugins.hostnames.html"
+    )
+    REPORTED = True
+
+
+def on_result(_request, _search, result):
+    # pylint: disable=import-outside-toplevel, cyclic-import
+    from searx.plugins.hostnames import on_result as hostnames_on_result
+
+    deprecated_msg()
+    return hostnames_on_result(_request, _search, result)

searx/plugins/hostnames.py

@@ -3,6 +3,16 @@
 """In addition to rewriting/replace reslut URLs, the *hoostnames* plugin offers
 other features.
 
+.. attention::
+
+   The 'Hostnames plugin' from `PR-3463
+   <https://github.com/searxng/searxng/pull/3463>`_ is a rewrite of the
+   'Hostname replace' plugin.  Backwards compatibility is guaranteed for a
+   transitional period, but this will end soon.
+
+   **To maintainers of SearXNG instances, please modify your old plugin config
+   to the new.**
+
 - ``hostnames.replace``: A mapping of regular expressions to hostnames to be
   replaced by other hostnames.
 
@@ -86,8 +96,29 @@ def _load_regular_expressions(settings_key):
     return {}
 
 
-replacements = _load_regular_expressions('replace')
-removables = _load_regular_expressions('remove')
+# compatibility fallback for old hostname replace plugin
+# TODO: remove in the future once most/all instance maintainers finished migrating # pylint: disable=fixme
+def _load_regular_expressions_with_fallback(settings_key):
+    expressions = _load_regular_expressions(settings_key)
+    if expressions:
+        return expressions
+
+    # fallback to the old `hostname_replace` settings format
+    # pylint: disable=import-outside-toplevel, cyclic-import
+    hostname_replace_config = settings.get('hostname_replace', {})
+    if hostname_replace_config:
+        from searx.plugins.hostname_replace import deprecated_msg
+
+        deprecated_msg()
+
+    if settings_key == 'replace':
+        return {re.compile(p): r for (p, r) in hostname_replace_config.items() if r}
+
+    return {re.compile(p) for (p, r) in hostname_replace_config.items() if not r}
+
+
+replacements = _load_regular_expressions_with_fallback('replace')
+removables = _load_regular_expressions_with_fallback('remove')
 high_priority = _load_regular_expressions('high_priority')
 low_priority = _load_regular_expressions('low_priority')