[PATCH 02 of 10] subrepo: use "vfs.tryread()" instead of explicit invocations of file APIs

[FUJIWARA Katsunori]

# HG changeset patch
# User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
# Date 1401288802 -32400
#      Wed May 28 23:53:22 2014 +0900
# Node ID 59f48202458c5236a65631c9a43425e8176245de
# Parent  25cb27f9fa274069475fc8d1a129a272d9d7e147
subrepo: use "vfs.tryread()" instead of explicit invocations of file APIs

This patch removes "_calcfilehash", because there is no code path
referring it.

This patch also avoids building absolute path "absname" up by
"self._repo.join" for files in "filelist", because "vfs.tryread"
doesn't need it.

diff --git a/mercurial/subrepo.py b/mercurial/subrepo.py
--- a/mercurial/subrepo.py
+++ b/mercurial/subrepo.py
@@ -31,14 +31,6 @@ def _getstorehashcachename(remotepath):
     '''get a unique filename for the store hash cache of a remote repository'''
     return util.sha1(_expandedabspath(remotepath)).hexdigest()[0:12]
 
-def _calcfilehash(filename):
-    data = ''
-    if os.path.exists(filename):
-        fd = open(filename, 'rb')
-        data = fd.read()
-        fd.close()
-    return util.sha1(data).hexdigest()
-
 class SubrepoAbort(error.Abort):
     """Exception class used to avoid handling a subrepo error more than once"""
     def __init__(self, *args, **kw):
@@ -554,9 +546,10 @@ class hgsubrepo(abstractsubrepo):
         # sort the files that will be hashed in increasing (likely) file size
         filelist = ('bookmarks', 'store/phaseroots', 'store/00changelog.i')
         yield '# %s\n' % _expandedabspath(remotepath)
+        vfs = self._repo.vfs
         for relname in filelist:
-            absname = os.path.normpath(self._repo.join(relname))
-            yield '%s = %s\n' % (relname, _calcfilehash(absname))
+            yield '%s = %s\n' % (relname,
+                                 util.sha1(vfs.tryread(relname)).hexdigest())
 
     def _getstorehashcachepath(self, remotepath):
         '''get a unique path for the store hash cache'''