Add the hook file's directory to sys.path (#3568)

Also clean sys.path after the hook is done, for some semblance of isolation

docs/user-guide/configuration.md

@@ -804,7 +804,7 @@ hooks:
   - my_hooks.py
 ```
 
-Then the file *my_hooks.py* can contain any [plugin event handlers](../dev-guide/plugins.md#events) (without `self`), e.g.:
+Then the file `my_hooks.py` can contain any [plugin event handlers](../dev-guide/plugins.md#events) (without `self`), e.g.:
 
 ```python
 def on_page_markdown(markdown, **kwargs):
@@ -843,6 +843,12 @@ You might have seen this feature in the [mkdocs-simple-hooks plugin](https://git
 +  - my_hooks.py
 ```
 
+> NEW: **New in MkDocs 1.6.**
+>
+> If a hook file has a file `foo.py` adjacent to it, it can use the normal Python syntax `import foo` to access its functions.
+>
+> In older versions of MkDocs, a workaround was necessary to make this work - adding the path to `sys.path`.
+
 ### plugins
 
 A list of plugins (with optional configuration settings) to use when building

mkdocs/config/config_options.py

@@ -1208,7 +1208,14 @@ def _load_hook(self, name, path):
         sys.modules[name] = module
         if spec.loader is None:
             raise ValidationError(f"Cannot import path '{path}' as a Python module")
-        spec.loader.exec_module(module)
+
+        old_sys_path = sys.path.copy()
+        sys.path.insert(0, os.path.dirname(path))
+        try:
+            spec.loader.exec_module(module)
+        finally:
+            sys.path[:] = old_sys_path
+
         return module
 
     def post_validation(self, config: Config, key_name: str):