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

searx/plugins/hostnames.py

@@ -41,8 +41,24 @@ 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
+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
+    hostname_replace_config = settings.get('hostname_replace', {})
+
+    if settings_key == 'replace':
+        return {re.compile(p): r for (p, r) in hostname_replace_config.items() if r != False}
+    else:
+        return {re.compile(p) for (p, r) in hostname_replace_config.items() if r == False}
+
+
+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')