tree 4e8e8bd242c88d4fddc3a6f2521789314b0ce239
parent fcc0c9ab67c5e237fa886ef7a105d96c1b264d27
author Ryan Hitchman <hitchman@sourcegraph.com> 1629578888 -0600
committer Ryan Hitchman <hitchman@sourcegraph.com> 1632941436 -0600

toc: modify disk format to include names for backwards/forwards compatiblity.

Including section names in the table of contents permits simpler
forwards and backwards compatibility. Instead of having to bump
the entire IndexFormatVersion when a new section is added, there is
simply a new section present in the table of contents.

Older versions can read TOCs with unknown sections and skip over them
with a warning. This is useful to permit downgrades without always
requiring a reindex.

Newer versions can read TOCs from older version with missing sections
and handle them gracefully, by checking for empty sections when loading
an index file and implementing whatever fallback code is necessary.

Section evolution is possible by having a new name for a tagged section,
adding the old section to the CompatibilityList, and writing the
conversion code when loading the file, or modifying the users of the
section to use whichever one is loaded.

Change-Id: I9aa05f29eb9d64fd0fff218f008d2031f1a15c8c