t0612: add tests to exercise Git/JGit reftable compatibility

While the reftable format is a recent introduction in Git, JGit already
knows to read and write reftables since 2017. Given the complexity of
the format there is a very real risk of incompatibilities between those
two implementations, which is something that we really want to avoid.

Add some basic tests that verify that reftables written by Git and JGit
can be read by the respective other implementation. For now this test
suite is rather small, only covering basic functionality. But it serves
as a good starting point and can be extended over time.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

t/t0612-reftable-jgit-compatibility.sh

@@ -0,0 +1,132 @@
+#!/bin/sh
+
+test_description='reftables are compatible with JGit'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+GIT_TEST_DEFAULT_REF_FORMAT=reftable
+export GIT_TEST_DEFAULT_REF_FORMAT
+
+# JGit does not support the 'link' DIRC extension.
+GIT_TEST_SPLIT_INDEX=0
+export GIT_TEST_SPLIT_INDEX
+
+. ./test-lib.sh
+
+if ! test_have_prereq JGIT
+then
+	skip_all='skipping reftable JGit tests; JGit is not present in PATH'
+	test_done
+fi
+
+if ! test_have_prereq SHA1
+then
+	skip_all='skipping reftable JGit tests; JGit does not support SHA256 reftables'
+	test_done
+fi
+
+test_commit_jgit () {
+	touch "$1" &&
+	jgit add "$1" &&
+	jgit commit -m "$1"
+}
+
+test_same_refs () {
+	git show-ref --head >cgit.actual &&
+	jgit show-ref >jgit-tabs.actual &&
+	tr "\t" " " <jgit-tabs.actual >jgit.actual &&
+	test_cmp cgit.actual jgit.actual
+}
+
+test_same_ref () {
+	git rev-parse "$1" >cgit.actual &&
+	jgit rev-parse "$1" >jgit.actual &&
+	test_cmp cgit.actual jgit.actual
+}
+
+test_same_reflog () {
+	git reflog "$*" >cgit.actual &&
+	jgit reflog "$*" >jgit-newline.actual &&
+	sed '/^$/d' <jgit-newline.actual >jgit.actual &&
+	test_cmp cgit.actual jgit.actual
+}
+
+test_expect_success 'CGit repository can be read by JGit' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A &&
+		test_same_refs &&
+		test_same_ref HEAD &&
+		test_same_reflog HEAD
+	)
+'
+
+test_expect_success 'JGit repository can be read by CGit' '
+	test_when_finished "rm -rf repo" &&
+	jgit init repo &&
+	(
+		cd repo &&
+
+		touch file &&
+		jgit add file &&
+		jgit commit -m "initial commit" &&
+
+		# Note that we must convert the ref storage after we have
+		# written the default branch. Otherwise JGit will end up with
+		# no HEAD at all.
+		jgit convert-ref-storage --format=reftable &&
+
+		test_same_refs &&
+		test_same_ref HEAD &&
+		# Interestingly, JGit cannot read its own reflog here. CGit can
+		# though.
+		printf "%s HEAD@{0}: commit (initial): initial commit" "$(git rev-parse --short HEAD)" >expect &&
+		git reflog HEAD >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'mixed writes from JGit and CGit' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+
+		test_commit A &&
+		test_commit_jgit B &&
+		test_commit C &&
+		test_commit_jgit D &&
+
+		test_same_refs &&
+		test_same_ref HEAD &&
+		test_same_reflog HEAD
+	)
+'
+
+test_expect_success 'JGit can read multi-level index' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+
+		test_commit A &&
+		awk "
+		    BEGIN {
+			print \"start\";
+			for (i = 0; i < 10000; i++)
+			    printf \"create refs/heads/branch-%d HEAD\n\", i;
+			print \"commit\";
+		    }
+		" >input &&
+		git update-ref --stdin <input &&
+
+		test_same_refs &&
+		test_same_ref refs/heads/branch-1 &&
+		test_same_ref refs/heads/branch-5738 &&
+		test_same_ref refs/heads/branch-9999
+	)
+'
+
+test_done