# HG changeset patch
# User Sune Foldager <cryo@cyanite.org>
# Date 2011-05-08 19:32:33
# Node ID d6907a5674a2d560bfa1790abca7a1593763c701
# Parent  66257848c1544e5e0ccf25858801f9a0ae7e549d

revlog: support writing generaldelta revlogs

With generaldelta switched on, deltas are always computed against the first
parent when adding revisions. This is done regardless of what revision the
incoming bundle, if any, is deltaed against.

The exact delta building strategy is subject to change, but this will not
affect compatibility.

Generaldelta is switched off by default.

diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -21,7 +21,7 @@ propertycache = util.propertycache
 class localrepository(repo.repository):
     capabilities = set(('lookup', 'changegroupsubset', 'branchmap', 'pushkey',
                         'known', 'getbundle'))
-    supportedformats = set(('revlogv1',))
+    supportedformats = set(('revlogv1', 'generaldelta'))
     supported = supportedformats | set(('store', 'fncache', 'shared',
                                         'dotencode'))
 
@@ -61,6 +61,8 @@ class localrepository(repo.repository):
                         '\0\0\0\2' # represents revlogv2
                         ' dummy changelog to prevent using the old repo layout'
                     )
+                if self.ui.configbool('format', 'generaldelta', False):
+                    requirements.append("generaldelta")
             else:
                 raise error.RepoError(_("repository %s not found") % path)
         elif create:
@@ -115,6 +117,8 @@ class localrepository(repo.repository):
     def _applyrequirements(self, requirements):
         self.requirements = requirements
         self.sopener.options = {}
+        if 'generaldelta' in requirements:
+            self.sopener.options['generaldelta'] = 1
 
     def _writerequirements(self):
         reqfile = self.opener("requires", "w")
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -226,10 +226,13 @@ class revlog(object):
         self._nodepos = None
 
         v = REVLOG_DEFAULT_VERSION
-        if hasattr(opener, 'options') and 'defversion' in opener.options:
-            v = opener.options['defversion']
-            if v & REVLOGNG:
-                v |= REVLOGNGINLINEDATA
+        if hasattr(opener, 'options'):
+            if 'defversion' in opener.options:
+                v = opener.options['defversion']
+                if v & REVLOGNG:
+                    v |= REVLOGNGINLINEDATA
+            if v & REVLOGNG and 'generaldelta' in opener.options:
+                v |= REVLOGGENERALDELTA
 
         i = ''
         try:
@@ -1003,10 +1006,14 @@ class revlog(object):
             l = len(data[1]) + len(data[0])
             basecache = self._basecache
             if basecache and basecache[0] == rev:
-                base = basecache[1]
+                chainbase = basecache[1]
             else:
-                base = self.chainbase(rev)
-            dist = l + offset - self.start(base)
+                chainbase = self.chainbase(rev)
+            dist = l + offset - self.start(chainbase)
+            if self._generaldelta:
+                base = rev
+            else:
+                base = chainbase
             return dist, l, data, base
 
         curr = len(self)
@@ -1019,7 +1026,10 @@ class revlog(object):
 
         # should we try to build a delta?
         if prev != nullrev:
-            d = builddelta(prev)
+            if self._generaldelta:
+                d = builddelta(p1r)
+            else:
+                d = builddelta(prev)
             dist, l, data, base = d
 
         # full versions are inserted when the needed deltas