python-setup: Handle poetry virtualenvs.options.no-pip = true

Fixes https://github.com/github/codeql-action/issues/1425

python-setup/find_site_packages.py

@@ -0,0 +1,28 @@
+"""
+Print the path to the site-packages directory for the current Python environment.
+"""
+
+try:
+    import pip
+    import os
+    print(os.path.dirname(os.path.dirname(pip.__file__)))
+except ImportError:
+    import sys
+    print("could not import pip", file=sys.stderr)
+    # if you use poetry with `virtualenvs.options.no-pip = true` you might end up with a
+    # virtualenv without pip, so the above trick doesn't actually work. See
+    # https://python-poetry.org/docs/configuration/#virtualenvsoptionsno-pip
+    #
+    # A possible option is to install `pip` into the virtualenv created by poetry
+    # (`poetry add pip`), but it turns out that doesn't always work :( for the test
+    # poetry/requests-3, I was not allowed to install pip! So I did not pursue this
+    # option further.
+    #
+    # Instead, local testing shows that first entry of `site.getsitepackages()` has the
+    # right path, whereas `site.getusersitepackages()` is about the system python (very
+    # confusing).
+    #
+    # We can't use the environment variable POETRY_VIRTUALENVS_OPTIONS_NO_PIP because it
+    # does not work, see https://github.com/python-poetry/poetry/issues/5906
+    import site
+    print(site.getsitepackages()[0])

python-setup/tests/from_python_exe.py

@@ -9,8 +9,7 @@ def get_details(path_to_python_exe: str) -> Tuple[str, str]:
     import_path = subprocess.check_output(
         [
             path_to_python_exe,
-            "-c",
-            "import os; import pip; print(os.path.dirname(os.path.dirname(pip.__file__)))",
+            os.path.join(os.path.dirname(__file__), "find_site_packages.py")
         ],
         stdin=subprocess.DEVNULL,
     )

python-setup/tests/poetry/requests-3/poetry.toml

@@ -1,2 +1,5 @@
 [virtualenvs]
 in-project = true
+
+[virtualenvs.options]
+no-pip = true