Allow plugin loading from external directory (#3364)

* Load custom plugin directories

* Allow plugins to be loaded from an external directory

* Handle exception when path is not relative to base path

* Fix typo

* Use pathlib

* Move plugin directory code into registry.py

- Allows us to reload plugins without having to reload the server itself

Co-authored-by: Matthias Mair <code@mjmair.com>

InvenTree/plugin/registry.py

@@ -187,6 +187,53 @@ class PluginsRegistry:
 
         logger.info('Finished reloading plugins')
 
+    def plugin_dirs(self):
+        """Construct a list of directories from where plugins can be loaded"""
+
+        dirs = ['plugin.builtin', ]
+
+        if settings.TESTING or settings.DEBUG:
+            # If in TEST or DEBUG mode, load plugins from the 'samples' directory
+            dirs.append('plugin.samples')
+
+        if settings.TESTING:
+            custom_dirs = os.getenv('INVENTREE_PLUGIN_TEST_DIR', None)
+        else:
+            custom_dirs = os.getenv('INVENTREE_PLUGIN_DIR', None)
+
+            # Load from user specified directories (unless in testing mode)
+            dirs.append('plugins')
+
+        if custom_dirs is not None:
+            # Allow multiple plugin directories to be specified
+            for pd_text in custom_dirs.split(','):
+                pd = pathlib.Path(pd_text.strip()).absolute()
+
+                # Attempt to create the directory if it does not already exist
+                if not pd.exists():
+                    try:
+                        pd.mkdir(exist_ok=True)
+                    except Exception:
+                        logger.error(f"Could not create plugin directory '{pd}'")
+                        continue
+
+                # Ensure the directory has an __init__.py file
+                init_filename = pd.joinpath('__init__.py')
+
+                if not init_filename.exists():
+                    try:
+                        init_filename.write_text("# InvenTree plugin directory\n")
+                    except Exception:
+                        logger.error(f"Could not create file '{init_filename}'")
+                        continue
+
+                if pd.exists() and pd.is_dir():
+                    # By this point, we have confirmed that the directory at least exists
+                    logger.info(f"Added plugin directory: '{pd}'")
+                    dirs.append(pd)
+
+        return dirs
+
     def collect_plugins(self):
         """Collect plugins from all possible ways of loading."""
         if not settings.PLUGINS_ENABLED:
@@ -196,8 +243,21 @@ class PluginsRegistry:
         self.plugin_modules = []  # clear
 
         # Collect plugins from paths
-        for plugin in settings.PLUGIN_DIRS:
-            modules = get_plugins(importlib.import_module(plugin), InvenTreePlugin)
+        for plugin in self.plugin_dirs():
+
+            print(f"Loading plugins from directory '{plugin}'")
+
+            parent_path = None
+            parent_obj = pathlib.Path(plugin)
+
+            # If a "path" is provided, some special handling is required
+            if parent_obj.name is not plugin and len(parent_obj.parts) > 1:
+                print("loading from a qualified path:", plugin)
+                parent_path = parent_obj.parent
+                plugin = parent_obj.name
+
+            modules = get_plugins(importlib.import_module(plugin), InvenTreePlugin, path=parent_path)
+
             if modules:
                 [self.plugin_modules.append(item) for item in modules]