[PATCH 2 of 6] scmutil: add a dirs class

[Bryan O'Sullivan]

# HG changeset patch
# User Bryan O'Sullivan <bryano at fb.com>
# Date 1364849265 25200
#      Mon Apr 01 13:47:45 2013 -0700
# Node ID eebf8fe7dea5ce3d262f89f848f2024c063b26e4
# Parent  cd42138d63c3110cbcd07b389f1d99920fb031ac
scmutil: add a dirs class

This encapsulates the "bag of directories" structures that are
currently open-coded (and duplicated) in both the dirstate and
context modules.

This will be used, and optionally replaced by a C implementation,
in upcoming changes.

diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -933,3 +933,37 @@ def finddirs(path):
     while pos != -1:
         yield path[:pos]
         pos = path.rfind('/', 0, pos)
+
+class dirs(object):
+    def __init__(self, m, skip=None):
+        self._dirs = {}
+        addpath = self.addpath
+        if util.safehasattr(m, 'iteritems') and skip is not None:
+            for f, s in m.iteritems():
+                if s[0] != skip:
+                    addpath(f)
+        else:
+            for f in m:
+                addpath(f)
+
+    def addpath(self, path):
+        dirs = self._dirs
+        for base in finddirs(path):
+            if base in dirs:
+                dirs[base] += 1
+                return
+            dirs[base] = 1
+
+    def delpath(self, path):
+        dirs = self._dirs
+        for base in finddirs(path):
+            if dirs[base] > 1:
+                dirs[base] -= 1
+                return
+            del dirs[base]
+
+    def __iter__(self):
+        return self._dirs.iterkeys()
+
+    def __contains__(self, d):
+        return d in self._dirs