subrepo: implement "storeclean" method for mercurial subrepos

The mercurial subrepo "storeclean" method works by calculating a "store hash" of
the repository state and comparing it to a cached store hash. The store hash is
always cached when the repository is cloned from or pushed to a remote
repository, but also on pull as long as the repository already had a clean
store. If the hashes match the store is "clean" versus the selected repository.

Note that this method is currenty unused, but it will be used by a later patch.

The store hash is calculated by hashing several key repository files, such as
the bookmarks file the phaseroots file and the changelog. Note that the hash
comparison is done file by file so that we can exit early if a pair of hashes
do not match. Also the hashes are calculated starting with the file that is
most likely to be smaller upto the file that is more likely to be larger.

mercurial/subrepo.py

@@ -446,6 +446,72 b' class hgsubrepo(abstractsubrepo):'
         self._repo.ui.setconfig('ui', '_usedassubrepo', 'True')
         self._initrepo(r, state[0], create)
 
+    def storeclean(self, path):
+        clean = True
+        lock = self._repo.lock()
+        itercache = self._calcstorehash(path)
+        try:
+            for filehash in self._readstorehashcache(path):
+                if filehash != itercache.next():
+                    clean = False
+                    break
+        except StopIteration:
+            # the cached and current pull states have a different size
+            clean = False
+        if clean:
+            try:
+                itercache.next()
+                # the cached and current pull states have a different size
+                clean = False
+            except StopIteration:
+                pass
+        lock.release()
+        return clean
+
+    def _calcstorehash(self, remotepath):
+        '''calculate a unique "store hash"
+
+        This method is used to to detect when there are changes that may
+        require a push to a given remote path.'''
+        # sort the files that will be hashed in increasing (likely) file size
+        filelist = ('bookmarks', 'store/phaseroots', 'store/00changelog.i')
+        yield '# %s\n' % remotepath
+        for relname in filelist:
+            absname = os.path.normpath(self._repo.join(relname))
+            yield '%s = %s\n' % (absname, _calcfilehash(absname))
+
+    def _getstorehashcachepath(self, remotepath):
+        '''get a unique path for the store hash cache'''
+        return self._repo.join(os.path.join(
+            'cache', 'storehash', _getstorehashcachename(remotepath)))
+
+    def _readstorehashcache(self, remotepath):
+        '''read the store hash cache for a given remote repository'''
+        cachefile = self._getstorehashcachepath(remotepath)
+        if not os.path.exists(cachefile):
+            return ''
+        fd = open(cachefile, 'r')
+        pullstate = fd.readlines()
+        fd.close()
+        return pullstate
+
+    def _cachestorehash(self, remotepath):
+        '''cache the current store hash
+
+        Each remote repo requires its own store hash cache, because a subrepo
+        store may be "clean" versus a given remote repo, but not versus another
+        '''
+        cachefile = self._getstorehashcachepath(remotepath)
+        lock = self._repo.lock()
+        storehash = list(self._calcstorehash(remotepath))
+        cachedir = os.path.dirname(cachefile)
+        if not os.path.exists(cachedir):
+            util.makedirs(cachedir, notindexed=True)
+        fd = open(cachefile, 'w')
+        fd.writelines(storehash)
+        fd.close()
+        lock.release()
+
     @annotatesubrepoerror
     def _initrepo(self, parentrepo, source, create):
         self._repo._subparent = parentrepo
@@ -564,13 +630,18 b' class hgsubrepo(abstractsubrepo):'
                                          update=False)
                 self._repo = cloned.local()
                 self._initrepo(parentrepo, source, create=True)
+                self._cachestorehash(srcurl)
             else:
                 self._repo.ui.status(_('pulling subrepo %s from %s\n')
                                      % (subrelpath(self), srcurl))
+                cleansub = self.storeclean(srcurl)
                 remotebookmarks = other.listkeys('bookmarks')
                 self._repo.pull(other)
                 bookmarks.updatefromremote(self._repo.ui, self._repo,
                                            remotebookmarks, srcurl)
+                if cleansub:
+                    # keep the repo clean after pull
+                    self._cachestorehash(srcurl)
 
     @annotatesubrepoerror
     def get(self, state, overwrite=False):
@@ -623,7 +694,11 b' class hgsubrepo(abstractsubrepo):'
         self._repo.ui.status(_('pushing subrepo %s to %s\n') %
             (subrelpath(self), dsturl))
         other = hg.peer(self._repo, {'ssh': ssh}, dsturl)
-        return self._repo.push(other, force, newbranch=newbranch)
+        res = self._repo.push(other, force, newbranch=newbranch)
+
+        # the repo is now clean
+        self._cachestorehash(dsturl)
+        return res
 
     @annotatesubrepoerror
     def outgoing(self, ui, dest, opts):