revlog: fix revlogio.packentry corner case

We want to store version information about the revlog in the first
entry of its index.  The code in packentry was using some heuristics
to detect whether this was the first entry, but these heuristics could
fail in some cases (e.g. rev 0 was empty; rev 1 descends directly from
the nullid and is stored as a delta).

We now give the revision number to packentry to avoid heuristics.

tests/test-revlog-packentry

@@ -0,0 +1,14 b''
+#!/bin/sh
+
+hg init repo
+cd repo
+
+touch foo
+hg ci -Am 'add foo'
+
+hg up -C null
+# this should be stored as a delta against rev 0
+echo foo bar baz > foo
+hg ci -Am 'add foo again'
+
+hg debugindex .hg/store/data/foo.i

tests/test-revlog-packentry.out

@@ -0,0 +1,6 b''
+adding foo
+0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+adding foo
+   rev    offset  length   base linkrev nodeid       p1           p2
+     0         0       0      0       0 b80de5d13875 000000000000 000000000000
+     1         0      24      0       1 0376abec49b8 000000000000 000000000000

mercurial/revlog.py

@@ -314,7 +314,7 b' class revlogoldio(object):'
 
         return index, nodemap, None
 
-    def packentry(self, entry, node, version):
+    def packentry(self, entry, node, version, rev):
         e2 = (getoffset(entry[0]), entry[1], entry[3], entry[4],
               node(entry[5]), node(entry[6]), entry[7])
         return _pack(indexformatv0, *e2)
@@ -388,9 +388,9 b' class revlogio(object):'
 
         return index, nodemap, cache
 
-    def packentry(self, entry, node, version):
+    def packentry(self, entry, node, version, rev):
         p = _pack(indexformatng, *entry)
-        if not entry[3] and not getoffset(entry[0]) and entry[5] == nullrev:
+        if rev == 0:
             p = _pack(versionformat, version) + p[4:]
         return p
 
@@ -972,7 +972,7 b' class revlog(object):'
         self.version &= ~(REVLOGNGINLINEDATA)
         self._inline = False
         for i in xrange(self.count()):
-            e = self._io.packentry(self.index[i], self.node, self.version)
+            e = self._io.packentry(self.index[i], self.node, self.version, i)
             fp.write(e)
 
         # if we don't call rename, the temp file will never replace the
@@ -1027,7 +1027,7 b' class revlog(object):'
         self.index.insert(-1, e)
         self.nodemap[node] = curr
 
-        entry = self._io.packentry(e, self.node, self.version)
+        entry = self._io.packentry(e, self.node, self.version, curr)
         if not self._inline:
             transaction.add(self.datafile, offset)
             transaction.add(self.indexfile, curr * len(entry))
@@ -1179,7 +1179,7 b' class revlog(object):'
                      link, self.rev(p1), self.rev(p2), node)
                 self.index.insert(-1, e)
                 self.nodemap[node] = r
-                entry = self._io.packentry(e, self.node, self.version)
+                entry = self._io.packentry(e, self.node, self.version, r)
                 if self._inline:
                     ifh.write(entry)
                     ifh.write(cdelta)