fix(plugin_utils): prioritize installed package import over relative cwd path in plugin loader

flexmeasures/utils/plugin_utils.py

@@ -42,24 +42,39 @@ def register_plugins(app: Flask):  # noqa: C901
         return
     app.config["LOADED_PLUGINS"] = {}
     for plugin in plugins:
-        plugin_name = plugin.split("/")[-1]
+        is_explicit_path = (
+            os.path.isabs(plugin)
+            or "/" in plugin
+            or (os.sep in plugin and os.sep != "/")
+            or plugin.startswith(".")
+        )
+        plugin_name = (
+            os.path.basename(os.path.normpath(plugin))
+            if is_explicit_path
+            else plugin
+        )
         app.logger.info(f"Importing plugin {plugin_name} ...")
         module = None
-        if not os.path.exists(plugin):  # assume plugin is a package
-            pkg_name = os.path.split(plugin)[
-                -1
-            ]  # rule out attempts for relative package imports
+        if not is_explicit_path:
+            pkg_name = plugin
             app.logger.debug(
                 f"Attempting to import {pkg_name} as an installed package ..."
             )
             try:
                 module = importlib.import_module(pkg_name)
             except ModuleNotFoundError:
-                app.logger.error(
-                    f"Attempted to import module {pkg_name} (as it is not a valid file path), but it is not installed."
-                )
-                continue
-        else:  # assume plugin is a file path
+                if os.path.exists(plugin):
+                    app.logger.warning(
+                        f"Plugin '{plugin}' is not installed in the environment; falling back to loading from relative path '{plugin}'."
+                    )
+                    is_explicit_path = True
+                else:
+                    app.logger.error(
+                        f"Attempted to import module {pkg_name} (as it is not a valid file path), but it is not installed."
+                    )
+                    continue
+
+        if is_explicit_path:
             if not os.path.exists(os.path.join(plugin, "__init__.py")):
                 app.logger.error(
                     f"Plugin {plugin_name} is a valid file path, but does not contain an '__init__.py' file. Cannot load plugin {plugin_name}."

flexmeasures/utils/tests/test_plugin_utils.py

@@ -0,0 +1,93 @@
+import os
+import sys
+import types
+import pytest
+from flask import Flask, Blueprint
+
+from flexmeasures.utils.plugin_utils import register_plugins
+
+
+def test_installed_plugin_not_shadowed_by_cwd_folder(tmp_path, monkeypatch):
+    """Test that an installed package is imported via import_module even if a folder with the same name exists in cwd."""
+    pkg_name = "test_installed_plugin_shadow"
+
+    # Create a mock installed module in sys.modules
+    mock_module = types.ModuleType(pkg_name)
+    mock_bp = Blueprint("installed_bp", pkg_name)
+    mock_module.installed_bp = mock_bp
+    mock_module.IS_INSTALLED = True
+    mock_module.__version__ = "1.0.0"
+
+    monkeypatch.setitem(sys.modules, pkg_name, mock_module)
+
+    # Create a same-named folder in tmp_path with a dummy __init__.py
+    plugin_dir = tmp_path / pkg_name
+    plugin_dir.mkdir()
+    (plugin_dir / "__init__.py").write_text("IS_INSTALLED = False\n", encoding="utf-8")
+
+    # Change working directory to tmp_path where the folder exists
+    monkeypatch.chdir(tmp_path)
+
+    app = Flask("test_app")
+    app.config["FLEXMEASURES_PLUGINS"] = [pkg_name]
+
+    register_plugins(app)
+
+    # Verify that the loaded plugin is the installed module and its Blueprint was registered
+    assert pkg_name in app.config["LOADED_PLUGINS"]
+    assert "installed_bp" in app.blueprints
+
+
+def test_explicit_file_path_plugin(tmp_path):
+    """Test that an explicit file path loads via spec_from_file_location."""
+    plugin_dir = tmp_path / "my_custom_filepath_plugin"
+    plugin_dir.mkdir()
+    init_file = plugin_dir / "__init__.py"
+    init_file.write_text(
+        "from flask import Blueprint\n"
+        "custom_bp = Blueprint('custom_bp', __name__)\n"
+        "__version__ = '2.0.0'\n",
+        encoding="utf-8",
+    )
+
+    app = Flask("test_app")
+    app.config["FLEXMEASURES_PLUGINS"] = [str(plugin_dir)]
+
+    register_plugins(app)
+
+    assert "my_custom_filepath_plugin" in app.config["LOADED_PLUGINS"]
+    assert "custom_bp" in app.blueprints
+
+
+def test_uninstalled_plugin_falls_back_to_relative_path(tmp_path, monkeypatch):
+    """Test that when a bare package name is not installed, it falls back to a relative folder in cwd with a warning."""
+    pkg_name = "uninstalled_fallback_plugin"
+    plugin_dir = tmp_path / pkg_name
+    plugin_dir.mkdir()
+    init_file = plugin_dir / "__init__.py"
+    init_file.write_text(
+        "from flask import Blueprint\n"
+        "fallback_bp = Blueprint('fallback_bp', __name__)\n",
+        encoding="utf-8",
+    )
+
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.delitem(sys.modules, pkg_name, raising=False)
+
+    app = Flask("test_app")
+    app.config["FLEXMEASURES_PLUGINS"] = [pkg_name]
+
+    register_plugins(app)
+
+    assert pkg_name in app.config["LOADED_PLUGINS"]
+    assert "fallback_bp" in app.blueprints
+
+
+def test_nonexistent_plugin_logs_error():
+    """Test that a plugin that neither exists as a package nor as a file path logs an error."""
+    app = Flask("test_app")
+    app.config["FLEXMEASURES_PLUGINS"] = ["nonexistent_package_xyz_123"]
+
+    register_plugins(app)
+
+    assert "nonexistent_package_xyz_123" not in app.config["LOADED_PLUGINS"]