+ def load_plugin_module(self, module_name: str, internal_path: str) -> Any:
+ """ Load a Python module as a plugin.
+
+ The module_name may have three variants:
+
+ * A name without any '.' is assumed to be an internal module
+ and will be searched relative to `internal_path`.
+ * If the name ends in `.py`, module_name is assumed to be a
+ file name relative to the project directory.
+ * Any other name is assumed to be an absolute module name.
+
+ In either of the variants the module name must start with a letter.
+ """
+ if not module_name or not module_name[0].isidentifier():
+ raise UsageError(f'Invalid module name {module_name}')
+
+ if '.' not in module_name:
+ module_name = module_name.replace('-', '_')
+ full_module = f'{internal_path}.{module_name}'
+ return sys.modules.get(full_module) or importlib.import_module(full_module)
+
+ if module_name.endswith('.py'):
+ if self.project_dir is None or not (self.project_dir / module_name).exists():
+ raise UsageError(f"Cannot find module '{module_name}' in project directory.")
+
+ if module_name in self._private_plugins:
+ return self._private_plugins[module_name]
+
+ file_path = str(self.project_dir / module_name)
+ spec = importlib.util.spec_from_file_location(module_name, file_path)
+ if spec:
+ module = importlib.util.module_from_spec(spec)
+ # Do not add to global modules because there is no standard
+ # module name that Python can resolve.
+ self._private_plugins[module_name] = module
+ assert spec.loader is not None
+ spec.loader.exec_module(module)
+
+ return module
+
+ return sys.modules.get(module_name) or importlib.import_module(module_name)
+
+