# HG changeset patch
# User Durham Goode <durham@fb.com>
# Date 2016-02-12 01:04:33
# Node ID 0b7ce0b16d8a629cee8610c62c16307ccefa5893
# Parent  65d24ca3549625aee4ccd4713bb745336610be40

pathauditor: change parts verification order to be root first

Previously, when we verified the parts of a path in the auditor, we would
validate the deepest directory first, then it's parent, and so on up to the
root. If there happened to be a symlink in the chain, that meant our first check
would likely traverse that symlink.  In some cases that symlink might point to
a network filesystem that is expensive, and therefore this simple check could be
very slow.

The fix is to check the path parts starting at the root and working our way
down.

This has a minor performance difference in that we used to be able to short
circuit from the audit if we reached a directory that had already been checked.
Now we can't, but the cost is N dictionary look ups, where N is the number of
parts in the path, which should be fairly minor.

diff --git a/mercurial/pathutil.py b/mercurial/pathutil.py
--- a/mercurial/pathutil.py
+++ b/mercurial/pathutil.py
@@ -83,16 +83,17 @@ class pathauditor(object):
         parts.pop()
         normparts.pop()
         prefixes = []
-        while parts:
-            prefix = os.sep.join(parts)
-            normprefix = os.sep.join(normparts)
+        # It's important that we check the path parts starting from the root.
+        # This means we won't accidentaly traverse a symlink into some other
+        # filesystem (which is potentially expensive to access).
+        for i in range(len(parts)):
+            prefix = os.sep.join(parts[:i + 1])
+            normprefix = os.sep.join(normparts[:i + 1])
             if normprefix in self.auditeddir:
-                break
+                continue
             if self._realfs:
                 self._checkfs(prefix, path)
             prefixes.append(normprefix)
-            parts.pop()
-            normparts.pop()
 
         self.audited.add(normpath)
         # only add prefixes to the cache after checking everything: we don't