Make app data override variable public (#1559)

docs/changelog/1559.feature.rst

@@ -0,0 +1 @@
+Allow virtualenv's app data cache to be overridden by ``VIRTUALENV_OVERRIDE_APP_DATA`` - by :user:`asottile`.

docs/user_guide.rst

@@ -127,6 +127,8 @@ main seed mechanism available:
   we can just link into the virtual environments install directory we can achieve speedups of shaving the initial
   1 minutes 10 seconds down to just 8 seconds in case of copy, or ``0.8`` seconds in case symlinks are available -
   this is on Windows, Linux/macOS with symlinks this can be as low as ``100ms`` from 3+ seconds).
+  To override the filesystem location of the seed cache, one can use the
+  ``VIRTUALENV_OVERRIDE_APP_DATA`` environment variable.
 
 Activators
 ----------

src/virtualenv/dirs.py

@@ -18,7 +18,7 @@ def default_data_dir():
 
 
 def _get_default_data_folder():
-    key = str("_VIRTUALENV_OVERRIDE_APP_DATA")
+    key = str("VIRTUALENV_OVERRIDE_APP_DATA")
     if key in os.environ:
         folder = os.environ[key]
     else:

tests/integration/test_zipapp.py

@@ -69,7 +69,7 @@ def zipapp_test_env(tmp_path_factory):
 @pytest.fixture()
 def call_zipapp(zipapp, monkeypatch, tmp_path, zipapp_test_env):
     def _run(*args):
-        monkeypatch.setenv(str("_VIRTUALENV_OVERRIDE_APP_DATA"), str(tmp_path / "app_data"))
+        monkeypatch.setenv(str("VIRTUALENV_OVERRIDE_APP_DATA"), str(tmp_path / "app_data"))
         cmd = [str(zipapp_test_env), str(zipapp), "-vv", six.ensure_text(str(tmp_path / "env"))] + list(args)
         subprocess.check_call(cmd)
 

tests/unit/create/test_creator.py

@@ -281,7 +281,7 @@ def test_cross_major(cross_python, coverage_env, tmp_path, current_fastest):
 
 
 def test_create_parallel(tmp_path, monkeypatch):
-    monkeypatch.setenv(str("_VIRTUALENV_OVERRIDE_APP_DATA"), str(tmp_path))
+    monkeypatch.setenv(str("VIRTUALENV_OVERRIDE_APP_DATA"), str(tmp_path))
 
     def create(count):
         subprocess.check_call([sys.executable, "-m", "virtualenv", str(tmp_path / "venv{}".format(count))])