annotate CONTRIBUTING @ 46547:5aac1a1a5beb

tagcache: distinguish between invalid and missing entries

The TortoiseHg repo has typically not had a newly applied tag accessible by name
for recent releases, for unknown reasons.  Deleting and rebuilding the tag cache
doesn't fix it, though deleting the cache and running `hg log -r $new_tag` does.
Eventually the situation does sort itself out for new clones from the server.
In an effort to figure out what the issue is, Pierre-Yves David suggested
listing these entries in the debug output more specifically.

This isn't complete yet- the second test change that says "missing" is more like
"invalid", since it was truncated.  The problem there is the code that reads the
raw array truncates any partial records and then fills it with 0xFF, which
signifies that it is missing.  As a side note, that means the check for the
length when validating an existing entry never fails.

Differential Revision: https://phab.mercurial-scm.org/D9811

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).