Add patch for buildkit to fetch by commit

[yosifkit]

Quick patch to get buildkit to attempt to fetch by digest.

Edit by @tianon: this is now simply a backport of moby/buildkit#5441 👀 🥳

[tianon]

(rebased, especially for #744)

[tianon]

Looks like we need to do some testing of moby/buildkit#5441! 👀

[tianon]

Rebased for 38eb63e, but now I'm going to update this to be a backport of moby/buildkit#5441 instead 👀

Edit: saving 7274d12...612102b for posterity (the original patch without the rebase noise; "thanks GitHubama")

[tianon]

Ok, there's a backport for 0.13, now to rebase on master to pick up the latest releases again 😭

[tianon]

Yesssssssss!!!! 🎉

$ docker buildx build --builder old --pull 'https://github.com/docker-library/mysql.git#e0d43b2a29867c5b7d5c01a8fea30a086861df2b:8.0' -f Dockerfile.oracle
#0 building with "old" instance using docker-container driver

#1 [internal] load git source https://github.com/docker-library/mysql.git#e0d43b2a29867c5b7d5c01a8fea30a086861df2b:8.0
Initialized empty Git repository in /var/lib/buildkit/runc-overlayfs/snapshots/snapshots/1/fs/
fatal: Not a valid object name e0d43b2a29867c5b7d5c01a8fea30a086861df2b^{commit}
From https://github.com/docker-library/mysql
 * branch            e0d43b2a29867c5b7d5c01a8fea30a086861df2b -> FETCH_HEAD
#1 DONE 0.9s

#2 [internal] load metadata for docker.io/library/oraclelinux:8-slim
#2 ...

[tianon]

Nice, fallback appears to work fine too:

$ docker buildx build --builder old --pull 'https://github.com/docker-library/mysql.git#ffffffffffffffffffffffffffffffffffffffff:8.0' -f Dockerfile.oracle
#0 building with "old" instance using docker-container driver

#1 [internal] load git source https://github.com/docker-library/mysql.git#ffffffffffffffffffffffffffffffffffffffff:8.0
fatal: Not a valid object name ffffffffffffffffffffffffffffffffffffffff^{commit}
fatal: remote error: upload-pack: not our ref ffffffffffffffffffffffffffffffffffffffff
From https://github.com/docker-library/mysql
 * [new branch]      jq-IN      -> origin/jq-IN
 * [new branch]      master     -> origin/master
fatal: reference is not a tree: ffffffffffffffffffffffffffffffffffffffff
#1 ERROR: failed to checkout remote https://github.com/docker-library/mysql.git: git error: exit status 128
stderr:
fatal: reference is not a tree: ffffffffffffffffffffffffffffffffffffffff

------
 > [internal] load git source https://github.com/docker-library/mysql.git#ffffffffffffffffffffffffffffffffffffffff:8.0:
fatal: Not a valid object name ffffffffffffffffffffffffffffffffffffffff^{commit}
fatal: remote error: upload-pack: not our ref ffffffffffffffffffffffffffffffffffffffff
From https://github.com/docker-library/mysql
 * [new branch]      jq-IN      -> origin/jq-IN
 * [new branch]      master     -> origin/master
fatal: reference is not a tree: ffffffffffffffffffffffffffffffffffffffff
------
ERROR: failed to solve: failed to read dockerfile: failed to checkout remote https://github.com/docker-library/mysql.git: git error: exit status 128
stderr:
fatal: reference is not a tree: ffffffffffffffffffffffffffffffffffffffff