On Fri, Apr 27, 2018 at 11:08 PM, brian m. carlson <sandals@xxxxxxxxxxxxxxxxxxxx> wrote: > On Thu, Apr 26, 2018 at 05:46:28PM +0200, Duy Nguyen wrote: >> On Wed, Apr 25, 2018 at 8:49 PM, Martin Ågren <martin.agren@xxxxxxxxx> wrote: >> > Once that is accomplished, I sort of suspect that this code will want to >> > be updated to not always blindly use the_hash_algo, but to always work >> > with SHA-1 sizes. Or rather, this would turn into more generic code to >> > handle both "v2 with SHA-1" and "v3 with some hash function(s)". This >> > commit might be a good first step in that direction. >> >> I also have an uneasy feeling when things this close to on-disk file >> format get hash-agnostic treatment. I think we would need to start >> adding new file formats soon, from bottom up with simple things like >> loose object files (cat-file and hash-object should be enough to test >> blobs...), then moving up to pack files and more. This is when we can >> really decide where to use the new hash and whether we should keep >> some hashes as sha-1. > > I agree that this is work which needs to be done soon. There are > basically a couple of pieces we need to handle NewHash: > > * Remove the dependencies on SHA-1 as much as possible. > * Get the tests to pass with a different hash (almost done for 160-bit > hash; in progress for 256-bit hashes). This step sounds good on paper but realistically could be a nightmare for you. I tried to implement a simple cat-file/hash-object combination with my imaginary newhash, which sounded straightforward to me since you have done a lot of heavylifting. To my surprise I hit a lot more problems. My point is, when I concentrate on just a few simple cases like this, I have a smaller scope to work with and could quickly identify problems. When you work on the scale of the test suite, it's really hard to know where the problem is (and you don't even know what areas are newhash-safe). Anyway my cat-file/hash-object modification could be found here. I probably will polish and send out a few good patches from it. https://github.com/pclouds/git/commits/new-hash -- Duy
