Fix deprecation warnings

src/mkdocstrings/loggers.py

@@ -4,7 +4,10 @@
 from pathlib import Path
 from typing import Any, Callable, Optional, Tuple
 
-from jinja2 import contextfunction
+try:
+    from jinja2 import pass_context
+except ImportError:
+    from jinja2 import contextfunction as pass_context
 from jinja2.runtime import Context
 from mkdocs.utils import warning_filter
 
@@ -71,7 +74,7 @@ def get_template_logger_function(logger_func: Callable) -> Callable:
         A function.
     """
 
-    @contextfunction
+    @pass_context
     def wrapper(context: Context, msg: Optional[str] = None) -> str:
         """Log a message.
 

src/mkdocstrings/plugin.py

@@ -122,14 +122,10 @@ def on_serve(self, server, builder: Callable, **kwargs):  # noqa: W0613 (unused
             server: The `livereload` server instance.
             builder: The function to build the site.
             kwargs: Additional arguments passed by MkDocs.
-
-        Returns:
-            The server instance.
         """
         for element in self.config["watch"]:
             log.debug(f"Adding directory '{element}' to watcher")
             server.watch(element, builder)
-        return server
 
     def on_config(self, config: Config, **kwargs) -> Config:  # noqa: W0613 (unused arguments)
         """Instantiate our Markdown extension.

tests/test_extension.py

@@ -24,6 +24,7 @@ def fixture_ext_markdown(request, tmp_path):
 
     conf_dict = {
         "site_name": "foo",
+        "site_url": "https://example.org/",
         "site_dir": str(tmp_path),
         "plugins": [{"mkdocstrings": {"default_handler": "python"}}],
         **getattr(request, "param", {}),