fixed FileNotFoundError when directory isn't writable (pypa#1640)

 - when using docker, if `user_data_dir()` isn't writable directory,
   `default_data_dir()` use `system temp directory` + `virtualenv`.
   for example, tempdir is `/tmp`, it use `/tmp/virtualenv`

src/virtualenv/dirs.py

@@ -1,4 +1,5 @@
 import os
+import tempfile
 
 from appdirs import user_config_dir, user_data_dir
 
@@ -23,9 +24,23 @@ def _get_default_data_folder():
         folder = os.environ[key]
     else:
         folder = user_data_dir(appname="virtualenv", appauthor="pypa")
+
+    if not _writable(folder):
+        folder = os.path.join(tempfile.gettempdir(), "virtualenv")
     return folder
 
 
+def _writable(folder) -> bool:
+    head = os.path.normpath(folder)
+
+    while not (os.path.exists(head) and os.access(head, os.W_OK)):
+        head, tail = os.path.split(head)
+        if not tail:
+            return False
+
+    return True
+
+
 def default_config_dir():
     from virtualenv.util.path import Path
 

tests/unit/test_dirs.py

@@ -0,0 +1,31 @@
+import logging
+import os
+import tempfile
+
+import appdirs
+
+from virtualenv import dirs
+from virtualenv.dirs import _get_default_data_folder
+
+
+def test_get_default_data_dir(monkeypatch):
+    # given
+    data_dirs = {
+        "/.local/share": os.path.join(tempfile.gettempdir(), "virtualenv"),
+        os.getenv('HOME'): os.path.join(os.getenv('HOME'), "virtualenv"),
+        "/tmp/share/": os.path.join("/tmp/share", "virtualenv")
+    }
+
+    def user_data_dir(data_dir):
+        def wrapper(appname=None, appauthor=None, version=None, roaming=False):
+            return os.path.join(data_dir, appname)
+        return wrapper
+
+    for data_dir, expected in data_dirs.items():
+        monkeypatch.setattr(dirs, "user_data_dir", user_data_dir(data_dir))
+
+        # when
+        actual = _get_default_data_folder()
+
+        # then
+        assert actual == expected