[PATCH v5 3/4] test-lib-functions: add helper for trailing hash

From: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Date: Jan 6, 2023, 16:31 UTC
Message-ID: <dab9b15de4794fd8ed45edff86ba89f4f63a335c.1673022717.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.1439.v5.git.1673022717.gitgitgadget@gmail.com>

From: Derrick Stolee <derrickstolee@github.com>

It can be helpful to check that a file format with a trailing hash has a specific hash in the final bytes of a written file. This is made more apparent by recent changes that allow skipping the hash algorithm and writing a null hash at the end of the file instead.

Add a new test_trailing_hash helper and use it in t1600 to verify that index.skipHash=true really does skip the hash computation, since 'git fsck' does not actually verify the hash. This confirms that when the config is disabled explicitly in a super project but enabled in a submodule, then the use of repo_config_get_bool() loads config from the correct repository in the case of 'git add'. There are other cases where istate->repo is NULL and thus this config is loaded instead from the_repository, but that's due to many different code paths initializing index_state structs in their own way.

Keep the 'git fsck' call to ensure that any potential future change to check the index hash does not cause an error in this case.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 t/t1600-index.sh        | 5 +++++
 t/test-lib-functions.sh | 8 ++++++++
 2 files changed, 13 insertions(+)

diff --git a/t/t1600-index.sh b/t/t1600-index.sh
index 98c5a83db73..2f792bb8ffa 100755
--- a/t/t1600-index.sh
+++ b/t/t1600-index.sh
@@ -68,6 +68,9 @@ test_expect_success 'out of bounds index.version issues warning' '
 test_expect_success 'index.skipHash config option' '
 	rm -f .git/index &&
 	git -c index.skipHash=true add a &&
+	test_trailing_hash .git/index >hash &&
+	echo $(test_oid zero) >expect &&
+	test_cmp expect hash &&
 	git fsck &&
 
 	test_commit start &&
@@ -76,6 +79,8 @@ test_expect_success 'index.skipHash config option' '
 	git -C sub config index.skipHash true &&
 	>sub/file &&
 	git -C sub add a &&
+	test_trailing_hash .git/modules/sub/index >hash &&
+	test_cmp expect hash &&
 	git -C sub fsck
 '
 
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 796093a7b32..60308843f8f 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1875,3 +1875,11 @@ test_cmp_config_output () {
 	sort config-actual >sorted-actual &&
 	test_cmp sorted-expect sorted-actual
 }
+
+# Given a filename, extract its trailing hash as a hex string
+test_trailing_hash () {
+	local file="$1" &&
+	tail -c $(test_oid rawsz) "$file" |
+		test-tool hexdump |
+		sed "s/ //g"
+}

-- 
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