Jonathan Nieder <> 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.
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