Try to make virtualenv metadata findable when invoked globally

deptry/cli.py

@@ -7,6 +7,10 @@
 from deptry.compat import metadata
 from deptry.config import read_configuration_from_pyproject_toml
 from deptry.core import Core
+from deptry.metadata_finder import (
+    install_metadata_finder,
+    warn_if_not_running_in_virtualenv,
+)
 from deptry.utils import PYPROJECT_TOML_PATH, run_within_dir
 
 
@@ -187,6 +191,12 @@ def display_deptry_version(ctx: click.Context, _param: click.Parameter, value: b
     expose_value=False,
     hidden=True,
 )
+@click.option(
+    "--python-site-packages",
+    "site_packages",
+    type=click.Path(exists=True, path_type=Path),
+    help="Path to the site-packages directory where dependencies are installed. Required if `deptry` is run while being installed globally.",
+)
 def deptry(
     root: Path,
     ignore_obsolete: Tuple[str, ...],
@@ -203,6 +213,7 @@ def deptry(
     requirements_txt: Tuple[str, ...],
     requirements_txt_dev: Tuple[str, ...],
     json_output: str,
+    site_packages: Path,
 ) -> None:
     """Find dependency issues in your Python project.
 
@@ -211,6 +222,11 @@ def deptry(
 
     """
 
+    if site_packages:
+        install_metadata_finder(site_packages)
+    else:
+        warn_if_not_running_in_virtualenv(root)
+
     with run_within_dir(root):
         Core(
             ignore_obsolete=ignore_obsolete,

deptry/metadata_finder.py

@@ -0,0 +1,79 @@
+import logging
+import os
+import sys
+from dataclasses import dataclass
+from pathlib import Path
+
+from deptry.compat import metadata
+
+
+@dataclass
+class ExecutionContext:
+    project_root: Path
+    base_prefix: str
+    prefix: str
+    active_virtual_env: str = None
+
+    @classmethod
+    def from_runtime(cls, project_root: Path):
+        return cls(
+            project_root=project_root,
+            base_prefix=sys.base_prefix,
+            prefix=sys.prefix,
+            active_virtual_env=os.environ.get("VIRTUAL_ENV"),
+        )
+
+    @property
+    def project_name(self):
+        return self.project_root.absolute().name
+
+    def running_in_project_virtualenv(self) -> bool:
+        """Determine if executed by the interpreter in the project's virtual environment
+
+        If we are executed from virtual environment, the context `prefix`
+        will be set to the virtual environment's directory, whereas
+        `base_prefix` will point to the global Python installation
+        used to create the virtual environment.
+
+        The `active_virtual_env` context field holds the value of the
+        VIRTUAL_ENV environment variable, that tells with good reliability
+        that a virtual environment has been activated in the current shell.
+        """
+
+        # Gobal installation
+        if self.prefix == self.base_prefix:
+            return False
+
+        # No virtualenv has been activated. Unless the project name is in
+        # the interpreter path, assume we are not in the project's virtualenv
+        if not self.active_virtual_env:
+            return self.project_name in self.prefix
+
+        # A virtualenv has been activated. But if `deptry` was installed gloabally using
+        # `pipx`, we could be running in another installation.
+        return self.active_virtual_env == self.prefix
+
+
+def install_metadata_finder(site_packages: Path) -> None:
+    """Add poject virtualenv site packages to metadata search path"""
+    path = [str(site_packages.absolute()), *sys.path]
+
+    class VirtualenvDistributionFinder(metadata.MetadataPathFinder):
+        @classmethod
+        def find_distributions(cls, context):
+            context = metadata.DistributionFinder.Context(name=context.name, path=path)
+            return super().find_distributions(context)
+
+    sys.meta_path.insert(0, VirtualenvDistributionFinder())
+
+
+def warn_if_not_running_in_virtualenv(root: Path) -> None:
+    ctx = ExecutionContext.from_runtime(root)
+    if not ctx.running_in_project_virtualenv():
+        log_msg = (
+            f"If deptry is not installed within the `{ctx.project_name}` project's virtual environment, it does not "
+            "have access to the metadata of dependencies installed within the virtual environment. This can be "
+            "solved by installing deptry in the virtual environment, or by passing the path to your virtual "
+            "environment's site-packages directory as the `--python-site-packages` argument."
+        )
+        logging.warn(log_msg)

tests/test_virtualenv_finder.py

@@ -0,0 +1,25 @@
+from pathlib import Path
+
+import pytest
+
+from deptry.metadata_finder import ExecutionContext
+
+
+@pytest.mark.parametrize(
+    "params, expected",
+    [
+        # Global installation
+        ((Path("theproject"), "/usr", "/usr", None), False),
+        # Direct invocation with project interpreter
+        ((Path("theproject"), "/usr", "/home/user/.virtualenvs/theproject", None), True),
+        # Pipx global install. Project virtualenv active
+        ((Path("theproject"), "/usr", "/home/user/.local/pipx/venvs/deptry", "/home/user/theproject/.venv"), False),
+        # Project virtualenv active and running
+        ((Path("theproject"), "/usr", "/home/user/theproject/.venv", "/home/user/theproject/.venv"), True),
+    ],
+)
+def test_running_in_project_virtualenv(params, expected):
+    arg_names = ("project_root", "base_prefix", "prefix", "active_virtual_env")
+    kwargs = dict(zip(arg_names, params))
+    ctx = ExecutionContext(**kwargs)
+    assert ctx.running_in_project_virtualenv() == expected