diff mercurial/changelog.py @ 43231:30570a056fa8

sidedatacopies: only store an entry if it has values

This will make for a shorter storage and help use to write faster code in simple
case. This change already provided a speed boost for copy tracing.

For example here is combined time of running copies tracing on a 6989 pairs of
revision on the pypy repos:

before: 771s
after:  631s - 18%

This also has a very positive impact on changelog size. For example here are the
number for the `00changelog.d` file of pypy.

before: 30449712 Bytes
after:  24973718 Bytes - 18%

This give an overall quite acceptable overhead for storing copies into the
changelog:

filelog-only: 23370586
sidedata:     24973718 Bytes + 7%

Differential Revision: https://phab.mercurial-scm.org/D7068

--- a/mercurial/changelog.py	Wed Oct 02 14:16:30 2019 -0400
+++ b/mercurial/changelog.py	Wed Oct 02 14:38:34 2019 -0400
@@ -693,14 +693,16 @@
                 extra[b'filesremoved'] = filesremoved
         elif self._copiesstorage == b'changeset-sidedata':
             sidedata = {}
-            if p1copies is not None:
+            if p1copies:
                 sidedata[sidedatamod.SD_P1COPIES] = p1copies
-            if p2copies is not None:
+            if p2copies:
                 sidedata[sidedatamod.SD_P2COPIES] = p2copies
-            if filesadded is not None:
+            if filesadded:
                 sidedata[sidedatamod.SD_FILESADDED] = filesadded
-            if filesremoved is not None:
+            if filesremoved:
                 sidedata[sidedatamod.SD_FILESREMOVED] = filesremoved
+            if not sidedata:
+                sidedata = None
 
         if extra:
             extra = encodeextra(extra)