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Date:   Wed, 15 May 2019 19:40:34 -0400
From:   "Eric S. Raymond" <esr@thyrsus.com>
To:     Jason Pyeron <jpyeron@pdinc.us>
Cc:     git@vger.kernel.org, 'Derrick Stolee' <stolee@gmail.com>
Subject: Re: Finer timestamps and serialization in git
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Jason Pyeron <jpyeron@pdinc.us>:
> If we take the below example:
> 
> committer Name <user@domain> 1557948240 -0400
> 
> and we follow the rule that:
> 
> 1. any trailing zero after the decimal point MUST be omitted
> 2. if there are no digits after the decimal point, it MUST be omitted
> 
> This would allow:
> 
> committer Name <user@domain> 1557948240 -0400
> committer Name <user@domain> 1557948240.12 -0400
> 
> but the following are never allowed:
> 
> committer Name <user@domain> 1557948240. -0400
> committer Name <user@domain> 1557948240.000000 -0400
> 
> By following these rules, all previous commits' hash are unchanged. Future commits made on the top of the second will look like old commit formats. Commits coming from "older" tools will produce valid and mergeable objects. The loss precision has frustrated us several times as well.

Yes, that's almost exactly what I came up with.  I was concerned with upward
compatibility in fast-export streams, which reposurgeon ingests and emits.

But I don't quite understand your claim that there's no format
breakage here, unless you're implying to me that timestamps are already
stored in the git file system as variable-length strings.  Do they
really never get translated into time_t?  Good news if so.
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>