feature(virtualenv): add 'system-site-packages' option

docs/docs/configuration.md

@@ -35,6 +35,7 @@ cache-dir = "/path/to/cache/directory"
 virtualenvs.create = true
 virtualenvs.in-project = null
 virtualenvs.options.always-copy = true
+virtualenvs.options.system-site-packages = false
 virtualenvs.path = "{cache-dir}/virtualenvs"  # /path/to/cache/directory/virtualenvs
 ```
 
@@ -143,6 +144,11 @@ Defaults to `{cache-dir}/virtualenvs` (`{cache-dir}\virtualenvs` on Windows).
 If set to `true` the `--always-copy` parameter is passed to `virtualenv` on creation of the venv. Thus all needed files are copied into the venv instead of symlinked.
 Defaults to `false`.
 
+### `virtualenvs.options.system-site-packages`: boolean
+
+Give the virtual environment access to the system site-packages directory.
+Applies on virtualenv creation.
+Defaults to `false`.
 
 ### `repositories.<name>`: string
 

poetry/config/config.py

@@ -35,7 +35,7 @@ class Config(object):
             "create": True,
             "in-project": None,
             "path": os.path.join("{cache-dir}", "virtualenvs"),
-            "options": {"always-copy": False},
+            "options": {"always-copy": False, "system-site-packages": False},
         },
         "experimental": {"new-installer": True},
         "installer": {"parallel": True},
@@ -140,6 +140,7 @@ def _get_normalizer(self, name: str) -> Callable:
             "virtualenvs.create",
             "virtualenvs.in-project",
             "virtualenvs.options.always-copy",
+            "virtualenvs.options.system-site-packages",
             "installer.parallel",
         }:
             return boolean_normalizer

poetry/console/commands/config.py

@@ -66,6 +66,16 @@ def unique_config_values(self) -> Dict[str, Tuple[Any, Any, Any]]:
             ),
             "virtualenvs.create": (boolean_validator, boolean_normalizer, True),
             "virtualenvs.in-project": (boolean_validator, boolean_normalizer, False),
+            "virtualenvs.options.always-copy": (
+                boolean_validator,
+                boolean_normalizer,
+                False,
+            ),
+            "virtualenvs.options.system-site-packages": (
+                boolean_validator,
+                boolean_normalizer,
+                False,
+            ),
             "virtualenvs.path": (
                 str,
                 lambda val: str(Path(val)),
@@ -76,11 +86,6 @@ def unique_config_values(self) -> Dict[str, Tuple[Any, Any, Any]]:
                 boolean_normalizer,
                 True,
             ),
-            "virtualenvs.options.always-copy": (
-                boolean_validator,
-                boolean_normalizer,
-                False,
-            ),
             "installer.parallel": (
                 boolean_validator,
                 boolean_normalizer,

poetry/utils/env.py

@@ -637,8 +637,8 @@ def create_venv(
 
         create_venv = self._poetry.config.get("virtualenvs.create")
         root_venv = self._poetry.config.get("virtualenvs.in-project")
-
         venv_path = self._poetry.config.get("virtualenvs.path")
+
         if root_venv:
             venv_path = cwd / ".venv"
         elif venv_path is None:

tests/console/commands/env/test_use.py

@@ -52,7 +52,7 @@ def test_activate_activates_non_existing_virtualenv_no_envs_file(
 
     venv_py37 = venv_cache / "{}-py3.7".format(venv_name)
     mock_build_env.assert_called_with(
-        venv_py37, executable="python3.7", flags={"always-copy": False}
+        venv_py37, executable="python3.7", flags={"always-copy": False, "system-site-packages": False}
     )
 
     envs_file = TOMLFile(venv_cache / "envs.toml")

tests/console/commands/test_config.py

@@ -32,6 +32,7 @@ def test_list_displays_default_value_if_not_set(tester, config, config_cache_dir
 virtualenvs.create = true
 virtualenvs.in-project = null
 virtualenvs.options.always-copy = false
+virtualenvs.options.system-site-packages = false
 virtualenvs.path = {path}  # {virtualenvs}
 """.format(
         cache=json.dumps(str(config_cache_dir)),
@@ -53,6 +54,7 @@ def test_list_displays_set_get_setting(tester, config, config_cache_dir):
 virtualenvs.create = false
 virtualenvs.in-project = null
 virtualenvs.options.always-copy = false
+virtualenvs.options.system-site-packages = false
 virtualenvs.path = {path}  # {virtualenvs}
 """.format(
         cache=json.dumps(str(config_cache_dir)),
@@ -96,6 +98,7 @@ def test_list_displays_set_get_local_setting(tester, config, config_cache_dir):
 virtualenvs.create = false
 virtualenvs.in-project = null
 virtualenvs.options.always-copy = false
+virtualenvs.options.system-site-packages = false
 virtualenvs.path = {path}  # {virtualenvs}
 """.format(
         cache=json.dumps(str(config_cache_dir)),

tests/test_factory.py

@@ -222,3 +222,5 @@ def test_create_poetry_with_local_config(fixture_dir):
 
     assert not poetry.config.get("virtualenvs.in-project")
     assert not poetry.config.get("virtualenvs.create")
+    assert not poetry.config.get("virtualenvs.options.always-copy")
+    assert not poetry.config.get("virtualenvs.options.system-site-packages")

tests/utils/test_env.py

@@ -159,7 +159,7 @@ def test_activate_activates_non_existing_virtualenv_no_envs_file(
     m.assert_called_with(
         Path(tmp_dir) / "{}-py3.7".format(venv_name),
         executable="python3.7",
-        flags={"always-copy": False},
+        flags={"always-copy": False, "system-site-packages": False},
     )
 
     envs_file = TOMLFile(Path(tmp_dir) / "envs.toml")
@@ -279,7 +279,7 @@ def test_activate_activates_different_virtualenv_with_envs_file(
     m.assert_called_with(
         Path(tmp_dir) / "{}-py3.6".format(venv_name),
         executable="python3.6",
-        flags={"always-copy": False},
+        flags={"always-copy": False, "system-site-packages": False},
     )
 
     assert envs_file.exists()
@@ -333,7 +333,7 @@ def test_activate_activates_recreates_for_different_patch(
     build_venv_m.assert_called_with(
         Path(tmp_dir) / "{}-py3.7".format(venv_name),
         executable="python3.7",
-        flags={"always-copy": False},
+        flags={"always-copy": False, "system-site-packages": False},
     )
     remove_venv_m.assert_called_with(Path(tmp_dir) / "{}-py3.7".format(venv_name))
 
@@ -661,7 +661,7 @@ def test_create_venv_tries_to_find_a_compatible_python_executable_using_generic_
     m.assert_called_with(
         config_virtualenvs_path / "{}-py3.7".format(venv_name),
         executable="python3",
-        flags={"always-copy": False},
+        flags={"always-copy": False, "system-site-packages": False},
     )
 
 
@@ -685,7 +685,7 @@ def test_create_venv_tries_to_find_a_compatible_python_executable_using_specific
     m.assert_called_with(
         config_virtualenvs_path / "{}-py3.9".format(venv_name),
         executable="python3.9",
-        flags={"always-copy": False},
+        flags={"always-copy": False, "system-site-packages": False},
     )
 
 
@@ -769,7 +769,7 @@ def test_create_venv_uses_patch_version_to_detect_compatibility(
         config_virtualenvs_path
         / "{}-py{}.{}".format(venv_name, version.major, version.minor),
         executable=None,
-        flags={"always-copy": False},
+        flags={"always-copy": False, "system-site-packages": False},
     )
 
 
@@ -804,7 +804,7 @@ def test_create_venv_uses_patch_version_to_detect_compatibility_with_executable(
         config_virtualenvs_path
         / "{}-py{}.{}".format(venv_name, version.major, version.minor - 1),
         executable="python{}.{}".format(version.major, version.minor - 1),
-        flags={"always-copy": False},
+        flags={"always-copy": False, "system-site-packages": False},
     )
 
 
@@ -838,7 +838,7 @@ def test_activate_with_in_project_setting_does_not_fail_if_no_venvs_dir(
     m.assert_called_with(
         poetry.file.parent / ".venv",
         executable="python3.7",
-        flags={"always-copy": False},
+        flags={"always-copy": False, "system-site-packages": False},
     )
 
     envs_file = TOMLFile(Path(tmp_dir) / "virtualenvs" / "envs.toml")
@@ -875,3 +875,17 @@ def test_venv_has_correct_paths(tmp_venv):
     assert paths.get("platlib") is not None
     assert paths.get("scripts") is not None
     assert tmp_venv.site_packages.path == Path(paths["purelib"])
+
+
+def test_env_system_packages(tmp_path, config):
+    venv_path = tmp_path / "venv"
+    pyvenv_cfg = venv_path / "pyvenv.cfg"
+
+    EnvManager(config).build_venv(path=venv_path, flags={"system-site-packages": True})
+
+    if sys.version_info >= (3, 3):
+        assert "include-system-site-packages = true" in pyvenv_cfg.read_text()
+    elif (2, 6) < sys.version_info < (3, 0):
+        assert not venv_path.joinpath(
+            "lib", "python2.7", "no-global-site-packages.txt"
+        ).exists()