Re: [PATCH 0/3] SHA-256: Update commit-graph and multi-pack-index formats

Derrick Stolee [off-list ref] writes:

On 8/14/2020 3:25 PM, Junio C Hamano wrote:

quoted

"Derrick Stolee via GitGitGadget" [off-list ref] writes:

quoted

As discussed [1], there is some concern around binary file formats requiring
the context of the repository config in order to infer hash lengths. Two
formats that were designed with the hash transition in mind (commit-graph
and multi-pack-index) have bytes available to indicate the hash algorithm
used. Let's actually update these formats to be more self-contained with the
two hash algorithms being available.
...
If this is the way we want to go with the formats, then I'll assist
coordinating these textual and semantic merge conflicts.

I agree that the files should be self-identifying, but have these
changes tested without sha256 hash?

All of the test scripts pass with and without GIT_TEST_DEFAULT_HASH=sha256,
and this test in t5318 (and a similar one in t5319) are explicit about
testing both options:

+test_expect_success 'warn on improper hash version' '
+	git init --object-format=sha1 sha1 &&
+	(
+		cd sha1 &&
+		test_commit 1 &&
+		git commit-graph write --reachable &&
+		mv .git/objects/info/commit-graph ../cg-sha1
+	) &&
+	git init --object-format=sha256 sha256 &&
+	(
+		cd sha256 &&
+		test_commit 1 &&
+		git commit-graph write --reachable &&
+		mv .git/objects/info/commit-graph ../cg-sha256
+	) &&
+	(
+		cd sha1 &&
+		mv ../cg-sha256 .git/objects/info/commit-graph &&
+		git log -1 2>err &&
+		test_i18ngrep "commit-graph hash version 2 does not match version 1" err
+	) &&
+	(
+		cd sha256 &&
+		mv ../cg-sha1 .git/objects/info/commit-graph &&
+		git log -1 2>err &&
+		test_i18ngrep "commit-graph hash version 1 does not match version 2" err
+	)
+'
+

Since this tests exactly that the "hash version" byte is the same in
a SHA-1 repo, this checks that the new version of Git writes backwards-
compatible data in SHA-1 repos.

Or are you hinting at a more subtle test scenario that I missed?

No, I was just wondering how ready we are, as the four tests looked
too easy ;-)