manifest/revlog: do not let the revlog cache mutable objects

If a buffer of an mutable object is passed to revlog.addrevision(), the revlog
will happily store it in its cache. Later when the revlog reuses the cached
entry, if the manifest modified the object in-between, all kind of bugs
appears.

We fix it by:
- passing immutable objects to addrevision() if they are already available
- only storing the text in the cache if it's of str type

Then we can remove the conversion of the cache entry to str() during
retrieval. That was probably just there hiding the bug for the common cases
but not really fixing it.

mercurial/manifest.py

@@ -132,9 +132,9 b' class manifest(revlog.revlog):'
             # if this is changed to support newlines in filenames,
             # be sure to check the templates/ dir again (especially *-raw.tmpl)
             hex, flags = revlog.hex, map.flags
-            text = ["%s\000%s%s\n" % (f, hex(map[f]), flags(f))
-                    for f in files]
-            arraytext = array.array('c', "".join(text))
+            text = ''.join("%s\000%s%s\n" % (f, hex(map[f]), flags(f))
+                           for f in files)
+            arraytext = array.array('c', text)
             cachedelta = None
         else:
             added, removed = changed
@@ -190,9 +190,9 b' class manifest(revlog.revlog):'
             if p1 != self.tip():
                 cachedelta = None
             arraytext = addlist
+            text = buffer(arraytext)
 
-        n = self.addrevision(buffer(arraytext), transaction, link,
-                             p1, p2, cachedelta)
+        n = self.addrevision(text, transaction, link, p1, p2, cachedelta)
         self._mancache = (n, map, arraytext)
 
         return n

mercurial/revlog.py

@@ -973,7 +973,7 b' class revlog(object):'
         if node == nullid:
             return ""
         if self._cache and self._cache[0] == node:
-            return str(self._cache[2])
+            return self._cache[2]
 
         # look up what we need to read
         text = None
@@ -988,7 +988,7 b' class revlog(object):'
         # do we have useful data cached?
         if self._cache and self._cache[1] >= base and self._cache[1] < rev:
             base = self._cache[1]
-            text = str(self._cache[2])
+            text = self._cache[2]
 
         self._loadindex(base, rev + 1)
         self._chunkraw(base, rev)
@@ -1111,7 +1111,8 b' class revlog(object):'
             ifh.write(data[1])
             self.checkinlinesize(transaction, ifh)
 
-        self._cache = (node, curr, text)
+        if type(text) == str: # only accept immutable objects
+            self._cache = (node, curr, text)
         return node
 
     def ancestor(self, a, b):