view CONTRIBUTING @ 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

Our full contribution guidelines are in our wiki, please see:

https://www.mercurial-scm.org/wiki/ContributingChanges

If you just want a checklist to follow, you can go straight to

https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist

If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).