env use: fail if python version is not supported by the project

src/poetry/utils/env/env_manager.py

@@ -395,7 +395,6 @@ def create_venv(
 
         create_venv = self._poetry.config.get("virtualenvs.create")
         in_project_venv = self.use_in_project_venv()
-        use_poetry_python = self._poetry.config.get("virtualenvs.use-poetry-python")
         venv_prompt = self._poetry.config.get("virtualenvs.prompt")
 
         specific_python_requested = python is not None
@@ -420,7 +419,7 @@ def create_venv(
             # If an executable has been specified, we stop there
             # and notify the user of the incompatibility.
             # Otherwise, we try to find a compatible Python version.
-            if specific_python_requested and use_poetry_python:
+            if specific_python_requested:
                 raise NoCompatiblePythonVersionFoundError(
                     self._poetry.package.python_versions,
                     python.patch_version.to_string(),

tests/console/commands/env/conftest.py

@@ -26,7 +26,9 @@ def venv_name(app: PoetryTestApplication) -> str:
 
 @pytest.fixture
 def venv_cache(tmp_path: Path) -> Path:
-    return tmp_path
+    path = tmp_path / "venv_cache"
+    path.mkdir()
+    return path
 
 
 @pytest.fixture(scope="module")

tests/console/commands/env/test_use.py

@@ -11,8 +11,10 @@
 
 from poetry.core.constraints.version import Version
 
+from poetry.console.commands.env.use import EnvUseCommand
 from poetry.toml.file import TOMLFile
 from poetry.utils.env import MockEnv
+from poetry.utils.env.python.exceptions import NoCompatiblePythonVersionFoundError
 from tests.console.commands.env.helpers import build_venv
 from tests.console.commands.env.helpers import check_output_wrapper
 
@@ -66,6 +68,10 @@ def test_activate_activates_non_existing_virtualenv_no_envs_file(
     mock_build_env = mocker.patch(
         "poetry.utils.env.EnvManager.build_venv", side_effect=build_venv
     )
+    envs_file = TOMLFile(venv_cache / "envs.toml")
+
+    assert not envs_file.exists()
+    assert not list(venv_cache.iterdir())
 
     tester.execute("3.7")
 
@@ -81,7 +87,6 @@ def test_activate_activates_non_existing_virtualenv_no_envs_file(
         prompt="simple-project-py3.7",
     )
 
-    envs_file = TOMLFile(venv_cache / "envs.toml")
     assert envs_file.exists()
     envs: dict[str, Any] = envs_file.read()
     assert envs[venv_name]["minor"] == "3.7"
@@ -94,6 +99,33 @@ def test_activate_activates_non_existing_virtualenv_no_envs_file(
     assert tester.io.fetch_output() == f"Using virtualenv: {venv_py37}\n"
 
 
+@pytest.mark.parametrize("use_poetry_python", [True, False])
+def test_activate_does_not_activate_non_existing_virtualenv_with_unsupported_version(
+    tester: CommandTester,
+    venv_cache: Path,
+    venv_name: str,
+    venvs_in_cache_config: None,
+    mocked_python_register: MockedPythonRegister,
+    with_no_active_python: MagicMock,
+    use_poetry_python: bool,
+) -> None:
+    mocked_python_register("3.7.1")
+    mocked_python_register("3.8.2")
+    command = tester.command
+    assert isinstance(command, EnvUseCommand)
+    command.poetry.package.python_versions = "~3.8"
+    command.poetry.config.merge(
+        {"virtualenvs": {"use-poetry-python": use_poetry_python}}
+    )
+
+    assert not list(venv_cache.iterdir())
+
+    with pytest.raises(NoCompatiblePythonVersionFoundError):
+        tester.execute("3.7")
+
+    assert not list(venv_cache.iterdir())
+
+
 def test_get_prefers_explicitly_activated_virtualenvs_over_env_var(
     tester: CommandTester,
     current_python: PythonVersion,

tests/utils/env/test_env_manager.py

@@ -991,14 +991,16 @@ def test_create_venv_fails_if_no_compatible_python_version_could_be_found(
     assert m.call_count == 0
 
 
+@pytest.mark.parametrize("use_poetry_python", [True, False])
 def test_create_venv_does_not_try_to_find_compatible_versions_with_executable(
     manager: EnvManager,
     poetry: Poetry,
     config: Config,
     mocker: MockerFixture,
     mocked_python_register: MockedPythonRegister,
+    use_poetry_python: bool,
 ) -> None:
-    config.config["virtualenvs"]["use-poetry-python"] = True
+    config.config["virtualenvs"]["use-poetry-python"] = use_poetry_python
     if "VIRTUAL_ENV" in os.environ:
         del os.environ["VIRTUAL_ENV"]