Create temp_dir if not exists (#2781)

Closes #2770

Author: q0w

docs/changelog/2770.bugfix.rst

@@ -0,0 +1 @@
+Create temp_dir if not exists - by :user:`q0w`.

docs/config.rst

@@ -172,7 +172,7 @@ Core
 
 .. conf::
    :keys: temp_dir
-   :default: {tox_root}/.temp
+   :default: {tox_root}/.tmp
 
    Directory where to put tox temporary files. For example: we create a hard link (if possible, otherwise new copy) in
    this directory for the project package. This ensures tox works correctly when having parallel runs (as each session

src/tox/tox_env/api.py

@@ -288,6 +288,7 @@ def _setup_env(self) -> None:
             if eq is False and old is not None:  # pragma: no branch  # recreate if already created and not equals
                 raise Recreate(f"env type changed from {old} to {conf}")
         self._handle_env_tmp_dir()
+        self._handle_core_tmp_dir()
 
     def _setup_with_env(self) -> None:  # noqa: B027 # empty abstract base class
         pass
@@ -303,6 +304,9 @@ def _handle_env_tmp_dir(self) -> None:
             ensure_empty_dir(env_tmp_dir)
         env_tmp_dir.mkdir(parents=True, exist_ok=True)
 
+    def _handle_core_tmp_dir(self) -> None:
+        self.core["temp_dir"].mkdir(parents=True, exist_ok=True)
+
     def _clean(self, transitive: bool = False) -> None:  # noqa: U100
         if self._run_state["clean"]:  # pragma: no branch
             return  # pragma: no cover

tests/tox_env/test_api.py

@@ -0,0 +1,18 @@
+from pathlib import Path
+
+from tox.pytest import ToxProjectCreator
+
+
+def test_ensure_temp_dir_exists(tox_project: ToxProjectCreator) -> None:
+    ini = "[testenv]\ncommands=python -c 'import os; os.path.exists(r\"{temp_dir}\")'"
+    project = tox_project({"tox.ini": ini})
+    result = project.run()
+    result.assert_success()
+
+
+def test_dont_cleanup_temp_dir(tox_project: ToxProjectCreator, tmp_path: Path) -> None:
+    (tmp_path / "foo" / "bar").mkdir(parents=True)
+    project = tox_project({"tox.ini": "[tox]\ntemp_dir=foo"})
+    result = project.run()
+    result.assert_success()
+    assert (tmp_path / "foo" / "bar").exists()