filestat: move __init__ to frompath constructor

filestat: move __init__ to frompath constructor

We're going to add a `fromfp` constructor soon, and this also allows a filestat
object for a non-existent file to be created.

--- a/mercurial/dirstate.py	Sat Jun 10 14:07:31 2017 -0700
+++ b/mercurial/dirstate.py	Sat Jun 10 14:09:54 2017 -0700
@@ -432,7 +432,8 @@
         self._map = {}
         self._copymap = {}
         # ignore HG_PENDING because identity is used only for writing
-        self._identity = util.filestat(self._opener.join(self._filename))
+        self._identity = util.filestat.frompath(
+            self._opener.join(self._filename))
         try:
             fp = self._opendirstatefile()
             try:

--- a/mercurial/util.py	Sat Jun 10 14:07:31 2017 -0700
+++ b/mercurial/util.py	Sat Jun 10 14:09:54 2017 -0700
@@ -1098,7 +1098,7 @@
     oldstat = None
     if os.path.lexists(dest):
         if checkambig:
-            oldstat = checkambig and filestat(dest)
+            oldstat = checkambig and filestat.frompath(dest)
         unlink(dest)
     if hardlink:
         # Hardlinks are problematic on CIFS (issue4546), do not allow hardlinks
@@ -1128,7 +1128,7 @@
             else:
                 shutil.copymode(src, dest)
                 if oldstat and oldstat.stat:
-                    newstat = filestat(dest)
+                    newstat = filestat.frompath(dest)
                     if newstat.isambig(oldstat):
                         # stat of copied file is ambiguous to original one
                         advanced = (oldstat.stat.st_mtime + 1) & 0x7fffffff
@@ -1506,13 +1506,18 @@
     exists. Otherwise, it is None. This can avoid preparative
     'exists()' examination on client side of this class.
     """
-    def __init__(self, path):
+    def __init__(self, stat):
+        self.stat = stat
+
+    @classmethod
+    def frompath(cls, path):
         try:
-            self.stat = os.stat(path)
+            stat = os.stat(path)
         except OSError as err:
             if err.errno != errno.ENOENT:
                 raise
-            self.stat = None
+            stat = None
+        return cls(stat)
 
     __hash__ = object.__hash__
 
@@ -1622,10 +1627,10 @@
         if not self._fp.closed:
             self._fp.close()
             filename = localpath(self.__name)
-            oldstat = self._checkambig and filestat(filename)
+            oldstat = self._checkambig and filestat.frompath(filename)
             if oldstat and oldstat.stat:
                 rename(self._tempname, filename)
-                newstat = filestat(filename)
+                newstat = filestat.frompath(filename)
                 if newstat.isambig(oldstat):
                     # stat of changed file is ambiguous to original one
                     advanced = (oldstat.stat.st_mtime + 1) & 0x7fffffff

--- a/mercurial/vfs.py	Sat Jun 10 14:07:31 2017 -0700
+++ b/mercurial/vfs.py	Sat Jun 10 14:09:54 2017 -0700
@@ -176,11 +176,11 @@
         """
         srcpath = self.join(src)
         dstpath = self.join(dst)
-        oldstat = checkambig and util.filestat(dstpath)
+        oldstat = checkambig and util.filestat.frompath(dstpath)
         if oldstat and oldstat.stat:
             def dorename(spath, dpath):
                 ret = util.rename(spath, dpath)
-                newstat = util.filestat(dpath)
+                newstat = util.filestat.frompath(dpath)
                 if newstat.isambig(oldstat):
                     # stat of renamed file is ambiguous to original one
                     return ret, newstat.avoidambig(dpath, oldstat)
@@ -625,12 +625,12 @@
     """
     def __init__(self, fh):
         super(checkambigatclosing, self).__init__(fh)
-        object.__setattr__(self, r'_oldstat', util.filestat(fh.name))
+        object.__setattr__(self, r'_oldstat', util.filestat.frompath(fh.name))
 
     def _checkambig(self):
         oldstat = self._oldstat
         if oldstat.stat:
-            newstat = util.filestat(self._origfh.name)
+            newstat = util.filestat.frompath(self._origfh.name)
             if newstat.isambig(oldstat):
                 # stat of changed file is ambiguous to original one
                 newstat.avoidambig(self._origfh.name, oldstat)