Subject: Re: [PATCHv2] write_index: optionally allow broken null sha1s

From: Junio C Hamano <[email-masked]>
Date: Sun, 25 Aug 2013 23:03:54 -0700

Jonathan Nieder <[email-masked]> writes:

> In other words, why not use something like this?
>
> 	write_index: optionally allow broken null sha1s
>
> 	Commit 4337b58 (do not write null sha1s to on-disk index, 2012-07-28)
> 	added a safety check preventing git from writing null sha1s into the
> 	index. The intent was to catch errors in other parts of the code that
> 	might let such an entry slip into the index (or worse, a tree).
>
> 	Some existing repositories have some invalid trees that contain null
> 	sha1s already, though.  Until 4337b58, a common way to clean this up
> 	would be to use git-filter-branch's index-filter to repair such broken
> 	entries.  That now fails when filter-branch tries to write out the
> 	index.
>
> 	Introduce a GIT_ALLOW_NULL_SHA1 environment variable to relax this check
> 	and make it easier to recover from such a history.

I found this version more readable than Peff's (albeit slightly).

> After this patch, do you think (in a separate change) it would make
> sense for cache-tree.c::update_one() to check for null sha1 and error
> out unless GIT_ALLOW_NULL_SHA1 is true?  That would let us get rid of
> the caveat from the last paragraph.

Hmm, interesting thought.