Re: [PATCH 2/2] fast-import: add special '-' blob reference to use the previous one.

[Junio C Hamano <gitster@pobox.com>]

"Shawn O. Pearce" <spearce@spearce.org> writes:

> Hmph, so if create a new path with a blob of "-" the repository
> will be corrupt because the zero id was used and error was produced.
>
> Actually I think you have the same bug in the prior patch with the
> mode being inherited.  I wonder if we shouldn't put error checking
> in too to validate that versions[0] describes a file entry.

Why are these patches necessary?

The proposed commit message describes what it does, but does not give hint
to even guess being able to use this new feature helps in what situation.
As far as I can see, these changes allow the exporter to say "this aspect
of the new data is the same as the previous one", but I thought that the
way in which fast-import works already revolves around "you have this
tree, and the next tree is different from it in this and that way."  Why
does one need be able to mention "this is the same as the previous one"
explicitly in the first place?