4 files changed, 163 insertions, 0 deletions
diff --git a/t/helper/test-reach.c b/t/helper/test-reach.c
index 5dd374379c..7314f6c0d8 100644
--- a/t/helper/test-reach.c
+++ b/t/helper/test-reach.c
@@ -116,6 +116,8 @@ int cmd__reach(int ac, const char **av)
 		       repo_in_merge_bases_many(the_repository, A, X_nr, X_array, 0));
 	else if (!strcmp(av[1], "is_descendant_of"))
 		printf("%s(A,X):%d\n", av[1], repo_is_descendant_of(r, A, X));
+	else if (!strcmp(av[1], "get_branch_base_for_tip"))
+		printf("%s(A,X):%d\n", av[1], get_branch_base_for_tip(r, A, X_array, X_nr));
 	else if (!strcmp(av[1], "get_merge_bases_many")) {
 		struct commit_list *list = NULL;
 		if (repo_get_merge_bases_many(the_repository,
diff --git a/t/perf/p1500-graph-walks.sh b/t/perf/p1500-graph-walks.sh
index e14e7620cc..5b23ce5db9 100755
--- a/t/perf/p1500-graph-walks.sh
+++ b/t/perf/p1500-graph-walks.sh
@@ -20,6 +20,21 @@ test_expect_success 'setup' '
 		echo tag-$ref ||
 		return 1
 	done >tags &&
+
+	echo "A:HEAD" >test-tool-refs &&
+	for line in $(cat refs)
+	do
+		echo "X:$line" >>test-tool-refs || return 1
+	done &&
+	echo "A:HEAD" >test-tool-tags &&
+	for line in $(cat tags)
+	do
+		echo "X:$line" >>test-tool-tags || return 1
+	done &&
+
+	commit=$(git commit-tree $(git rev-parse HEAD^{tree})) &&
+	git update-ref refs/heads/disjoint-base $commit &&
+
 	git commit-graph write --reachable
 '
 
@@ -47,4 +62,20 @@ test_perf 'contains: git tag --merged' '
 	xargs git tag --merged=HEAD <tags
 '
 
+test_perf 'is-base check: test-tool reach (refs)' '
+	test-tool reach get_branch_base_for_tip <test-tool-refs
+'
+
+test_perf 'is-base check: test-tool reach (tags)' '
+	test-tool reach get_branch_base_for_tip <test-tool-tags
+'
+
+test_perf 'is-base check: git for-each-ref' '
+	git for-each-ref --format="%(is-base:HEAD)" --stdin <refs
+'
+
+test_perf 'is-base check: git for-each-ref (disjoint-base)' '
+	git for-each-ref --format="%(is-base:refs/heads/disjoint-base)" --stdin <refs
+'
+
 test_done
diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index eb6c8204e8..8d15713cc6 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -1907,6 +1907,15 @@ test_expect_success 'git for-each-ref with nested tags' '
 	test_cmp expect actual
 '
 
+test_expect_success 'is-base atom with non-commits' '
+	git for-each-ref --format="%(is-base:HEAD) %(refname)" >out 2>err &&
+	grep "(HEAD) refs/heads/main" out &&
+
+	test_line_count = 2 err &&
+	grep "error: object .* is a commit, not a blob" err &&
+	grep "error: bad tag pointer to" err
+'
+
 GRADE_FORMAT="%(signature:grade)%0a%(signature:key)%0a%(signature:signer)%0a%(signature:fingerprint)%0a%(signature:primarykeyfingerprint)"
 TRUSTLEVEL_FORMAT="%(signature:trustlevel)%0a%(signature:key)%0a%(signature:signer)%0a%(signature:fingerprint)%0a%(signature:primarykeyfingerprint)"
 
diff --git a/t/t6600-test-reach.sh b/t/t6600-test-reach.sh
index b330945f49..2591f8b8b3 100755
--- a/t/t6600-test-reach.sh
+++ b/t/t6600-test-reach.sh
@@ -612,4 +612,125 @@ test_expect_success 'for-each-ref merged:none' '
 		--format="%(refname)" --stdin
 '
 
+# For get_branch_base_for_tip, we only care about
+# first-parent history. Here is the test graph with
+# second parents removed:
+#
+#             (10,10)
+#            /
+#         (10,9)    (9,10)
+#        /         /
+#    (10,8)    (9,9)      (8,10)
+#   /         /          /
+#         ( continued...)
+#   \     /        /           /
+#    (3,1)     (2,2)      (1,3)
+#        \     /          /
+#         (2,1)      (1,2)
+#              \    /
+#              (1,1)
+#
+# In short, for a commit (i,j), the first-parent history
+# walks all commits (i, k) with k from j to 1, then the
+# commits (l, 1) with l from i to 1.
+
+test_expect_success 'get_branch_base_for_tip: none reach' '
+	# (2,3) branched from the first tip (i,4) in X with i > 2
+	cat >input <<-\EOF &&
+		A:commit-2-3
+		X:commit-1-2
+		X:commit-1-4
+		X:commit-4-4
+		X:commit-8-4
+		X:commit-10-4
+	EOF
+	echo "get_branch_base_for_tip(A,X):2" >expect &&
+	test_all_modes get_branch_base_for_tip
+'
+
+test_expect_success 'get_branch_base_for_tip: equal to tip' '
+	# (2,3) branched from the first tip (i,4) in X with i > 2
+	cat >input <<-\EOF &&
+		A:commit-8-4
+		X:commit-1-2
+		X:commit-1-4
+		X:commit-4-4
+		X:commit-8-4
+		X:commit-10-4
+	EOF
+	echo "get_branch_base_for_tip(A,X):3" >expect &&
+	test_all_modes get_branch_base_for_tip
+'
+
+test_expect_success 'get_branch_base_for_tip: all reach tip' '
+	# (2,3) branched from the first tip (i,4) in X with i > 2
+	cat >input <<-\EOF &&
+		A:commit-4-1
+		X:commit-4-2
+		X:commit-5-1
+	EOF
+	echo "get_branch_base_for_tip(A,X):0" >expect &&
+	test_all_modes get_branch_base_for_tip
+'
+
+test_expect_success 'for-each-ref is-base: none reach' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-4-2
+	refs/heads/commit-4-4
+	refs/heads/commit-8-4
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-1-1:
+	refs/heads/commit-4-2:(commit-2-3)
+	refs/heads/commit-4-4:
+	refs/heads/commit-8-4:
+	EOF
+	run_all_modes git for-each-ref \
+		--format="%(refname):%(is-base:commit-2-3)" --stdin
+'
+
+test_expect_success 'for-each-ref is-base: all reach' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-4-2
+	refs/heads/commit-5-1
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-4-2:(commit-4-1)
+	refs/heads/commit-5-1:
+	EOF
+	run_all_modes git for-each-ref \
+		--format="%(refname):%(is-base:commit-4-1)" --stdin
+'
+
+test_expect_success 'for-each-ref is-base: equal to tip' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-4-2
+	refs/heads/commit-5-1
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-4-2:(commit-4-2)
+	refs/heads/commit-5-1:
+	EOF
+	run_all_modes git for-each-ref \
+		--format="%(refname):%(is-base:commit-4-2)" --stdin
+'
+
+test_expect_success 'for-each-ref is-base:multiple' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-4-2
+	refs/heads/commit-4-4
+	refs/heads/commit-8-4
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-1-1[-]
+	refs/heads/commit-4-2[(commit-2-3)-]
+	refs/heads/commit-4-4[-]
+	refs/heads/commit-8-4[-(commit-6-5)]
+	EOF
+	run_all_modes git for-each-ref \
+		--format="%(refname)[%(is-base:commit-2-3)-%(is-base:commit-6-5)]" --stdin
+'
+
 test_done