feat: install missing Python versions for virtualenv with pyenv

ghstack-source-id: c1e16c81bf4cd18a44dd656eb73963e1a3754706
Pull Request resolved: #52

src/isolate/backends/virtualenv.py

@@ -77,17 +77,38 @@ def install_requirements(self, path: Path) -> None:
             except subprocess.SubprocessError as exc:
                 raise EnvironmentCreationError("Failure during 'pip install'.") from exc
 
+    def _install_python_through_pyenv(self) -> str:
+        from isolate.backends.pyenv import PyenvEnvironment
+
+        self.log(
+            f"Requested Python version of {self.python_version} is not available "
+            "in the system, attempting to install it through pyenv."
+        )
+
+        pyenv = PyenvEnvironment.from_config(
+            {"python_version": self.python_version},
+            settings=self.settings,
+        )
+        return str(get_executable_path(pyenv.create(), "python"))
+
     def _decide_python(self) -> str:
         from virtualenv.discovery import builtin
 
+        from isolate.backends.pyenv import _get_pyenv_executable
+
         interpreter = builtin.get_interpreter(self.python_version, ())
         if interpreter is not None:
             return interpreter.executable
 
-        raise EnvironmentCreationError(
-            f"Python {self.python_version} is not available in your "
-            "system. Please install it first."
-        )
+        try:
+            _get_pyenv_executable()
+        except Exception:
+            raise EnvironmentCreationError(
+                f"Python {self.python_version} is not available in your "
+                "system. Please install it first."
+            ) from None
+        else:
+            return self._install_python_through_pyenv()
 
     def create(self) -> Path:
         from virtualenv import cli_run

tests/test_backends.py

@@ -278,7 +278,12 @@ def test_caching_with_constraints(self, tmp_path):
         )
         assert environment_1.key != environment_2.key != environment_3.key
 
-    def test_custom_python_version(self, tmp_path):
+    def test_custom_python_version(self, tmp_path, monkeypatch):
+        # Disable pyenv to prevent auto-installation
+        monkeypatch.setattr(
+            "isolate.backends.pyenv._get_pyenv_executable", lambda: 1 / 0
+        )
+
         for python_type, expected_python_version in [
             ("old-python", "3.7"),
             ("new-python", "3.10"),
@@ -294,7 +299,12 @@ def test_custom_python_version(self, tmp_path):
             python_version = self.get_python_version(environment, connection)
             assert python_version.startswith(expected_python_version)
 
-    def test_invalid_python_version_raises(self, tmp_path):
+    def test_invalid_python_version_raises(self, tmp_path, monkeypatch):
+        # Disable pyenv to prevent auto-installation
+        monkeypatch.setattr(
+            "isolate.backends.pyenv._get_pyenv_executable", lambda: 1 / 0
+        )
+
         # Hopefully there will never be a Python 9.9.9
         environment = self.get_environment(tmp_path, {"python_version": "9.9.9"})
         with pytest.raises(
@@ -636,3 +646,27 @@ def test_pyenv_environment(python_version, tmp_path):
 
     different_python.destroy(connection_key)
     assert not different_python.exists()
+
+
+@pytest.mark.skipif(not IS_PYENV_AVAILABLE, reason="Pyenv is not available")
+def test_virtual_env_custom_python_version_with_pyenv(tmp_path, monkeypatch):
+    pyjokes_env = VirtualPythonEnvironment(
+        requirements=["pyjokes==0.6.0"],
+        python_version="3.9",
+    )
+
+    test_settings = IsolateSettings(Path(tmp_path))
+    pyjokes_env.apply_settings(test_settings)
+
+    # Force it to choose pyenv as the python version manager.
+    pyjokes_env._decide_python = pyjokes_env._install_python_through_pyenv
+
+    connection_key = pyjokes_env.create()
+    with pyjokes_env.open_connection(connection_key) as connection:
+        assert connection.run(partial(eval, "__import__('sys').version")).startswith(
+            "3.9"
+        )
+        assert (
+            connection.run(partial(eval, "__import__('pyjokes').__version__"))
+            == "0.6.0"
+        )