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

Jonathan Nieder [off-list ref] 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.