Return to baseline with more aggressive can_write_dir check.

pex/common.py

@@ -515,21 +515,16 @@ def can_write_dir(path):
     # type: (str) -> bool
     """Determines if the directory at path can be written to by the current process.
 
-    If the directory doesn't exist, determines if it can be created and thus written to.
-
-    N.B.: This is a best-effort check only that uses permission heuristics and does not actually test
-    that the directory can be written to with and writes.
+    Attempts to create the directory if it doesn't already exist.
 
     :param path: The directory path to test.
     :return:`True` if the given path is a directory that can be written to by the current process.
     """
-    while not os.access(path, os.F_OK):
-        parent_path = os.path.dirname(path)
-        if not parent_path or (parent_path == path):
-            # We've recursed up to the root without success, which shouldn't happen,
-            return False
-        path = parent_path
-    return os.path.isdir(path) and os.access(path, os.R_OK | os.W_OK | os.X_OK)
+    try:
+        os.unlink(touch(os.path.join(path, ".write-test")))
+        return True
+    except (IOError, OSError):
+        return False
 
 
 def touch(

pex/variables.py

@@ -171,17 +171,7 @@ def _default_pex_root():
     # third party import lifecycle events.
     from pex.cache import root as cache_root
 
-    pex_root = cache_root.path(expand_user=True)
-    if not can_write_dir(pex_root):
-        tmp_root = os.path.realpath(safe_mkdtemp())
-        pex_warnings.warn(
-            "The default PEX_ROOT is {pex_root} but that path is un-writeable, falling back to a "
-            "temporary PEX_ROOT of {tmp_root} which will hurt performance.".format(
-                pex_root=pex_root, tmp_root=tmp_root
-            )
-        )
-        pex_root = tmp_root
-    return pex_root
+    return cache_root.path(expand_user=True)
 
 
 class Variables(object):

tests/integration/test_issue_1598.py

@@ -23,7 +23,7 @@ def test_mount_respects_env(
     pex_root = os.path.join(home, rel_pex_root)
     os.makedirs(pex_root)
     os.chmod(pex_root, 0o555)
-    unwritable_pex_root_warning = "PEXWarning: The default PEX_ROOT is {}".format(pex_root)
+    unwritable_pex_root_warning = "PEXWarning: PEX_ROOT is configured as {}".format(pex_root)
 
     pex_file = os.path.join(str(tmpdir), "pex.pex")