revlog: apply compression mode while reading sidedata

Right now, we only store things as PLAIN, but we are ready for some compression
now. Future changeset will start using some.

Differential Revision: https://phab.mercurial-scm.org/D10654

mercurial/revlog.py

@@ -2061,7 +2061,19 b' class revlog(object):'
         if sidedata_size == 0:
             return {}
 
-        segment = self._getsegment(sidedata_offset, sidedata_size)
+        comp_segment = self._getsegment(sidedata_offset, sidedata_size)
+        comp = self.index[rev][11]
+        if comp == COMP_MODE_PLAIN:
+            segment = comp_segment
+        elif comp == COMP_MODE_DEFAULT:
+            segment = self._decompressor(comp_segment)
+        elif comp == COMP_MODE_INLINE:
+            segment = self.decompress(comp_segment)
+        else:
+            msg = 'unknown compression mode %d'
+            msg %= comp
+            raise error.RevlogError(msg)
+
         sidedata = sidedatautil.deserialize_sidedata(segment)
         return sidedata