Groff History in Git. (Was: groff in git)

[Ralph Corderoy]

Hi Dave,

> Eric, can reposurgeon retroactively add an earlier release to git
> without changing all the existing git hashes (which are referenced all
> over the place, in the bug tracker and elsewhere)?  I know nothing
> about how these hashes are generated, so this may be utterly
> infeasible.

A Git commit ID is effectively a hash of its ancestry so that history
can't be changed in this case without the unwanted ripple.

If the groff Git repository had an empty ‘epoch’ commit from which
everything descended then other old versions could descend from that
without affecting existing descendants, but I don't think it has.  The
oldest commit looks to be for 1.02.
https://git.savannah.gnu.org/cgit/groff.git/commit/?h=1.04&id=351da0dcdf702cf243d26ffa998961bce2aa8653

If the epoch commit had existed then the new contributions wouldn't have
been in their correct location, e.g. 1.03 wouldn't be between 1.02 and
1.04, but Git's various searches could still have included them.

The alternative is to have a Git repo specifically for maintaining
historical versions, not for development, and then the commit IDs can be
completely regenerated as new discoveries are inserted.  This is what
Spinellis does for his
https://github.com/dspinellis/unix-history-repo#readme

-- 
Cheers, Ralph.