Merge branch 'bc/submodule-force-same-hash' into seen

Adding a repository that uses a different hash function is a no-no,
but "git submodule add" did nt prevent it, which has been corrected.

* bc/submodule-force-same-hash:
  object-file: disallow adding submodules of different hash algo

Author: gitster

object-file.c

@@ -1620,7 +1620,11 @@ int index_path(struct index_state *istate, struct object_id *oid,
 		strbuf_release(&sb);
 		break;
 	case S_IFDIR:
-		return repo_resolve_gitlink_ref(istate->repo, path, "HEAD", oid);
+		if (repo_resolve_gitlink_ref(istate->repo, path, "HEAD", oid))
+			return -1;
+		if (&hash_algos[oid->algo] != istate->repo->hash_algo)
+			return error(_("cannot add a submodule of a different hash algorithm"));
+		break;
 	default:
 		return error(_("%s: unsupported file type"), path);
 	}

t/t3700-add.sh

@@ -541,6 +541,33 @@ test_expect_success 'all statuses changed in folder if . is given' '
 	)
 '
 
+test_expect_success 'cannot add a submodule of a different algorithm' '
+	git init --object-format=sha256 sha256 &&
+	(
+		cd sha256 &&
+		test_commit abc &&
+		git init --object-format=sha1 submodule &&
+		(
+			cd submodule &&
+			test_commit def
+		) &&
+		test_must_fail git add submodule &&
+		test $(git ls-files --stage | grep ^160000 | wc -l) -eq 0
+	) &&
+	git init --object-format=sha1 sha1 &&
+	(
+		cd sha1 &&
+		test_commit abc &&
+		git init --object-format=sha256 submodule &&
+		(
+			cd submodule &&
+			test_commit def
+		) &&
+		test_must_fail git add submodule &&
+		test $(git ls-files --stage | grep ^160000 | wc -l) -eq 0
+	)
+'
+
 test_expect_success CASE_INSENSITIVE_FS 'path is case-insensitive' '
 	path="$(pwd)/BLUB" &&
 	touch "$path" &&

t/t7400-submodule-basic.sh

@@ -407,6 +407,33 @@ test_expect_success 'submodule add in subdirectory with relative path should fai
 	test_grep toplevel output.err
 '
 
+test_expect_success 'submodule add of a different algorithm fails' '
+	git init --object-format=sha256 sha256 &&
+	(
+		cd sha256 &&
+		test_commit abc &&
+		git init --object-format=sha1 submodule &&
+		(
+			cd submodule &&
+			test_commit def
+		) &&
+		test_must_fail git submodule add "$submodurl" submodule &&
+		test $(git ls-files --stage | grep ^160000 | wc -l) -eq 0
+	) &&
+	git init --object-format=sha1 sha1 &&
+	(
+		cd sha1 &&
+		test_commit abc &&
+		git init --object-format=sha256 submodule &&
+		(
+			cd submodule &&
+			test_commit def
+		) &&
+		test_must_fail git submodule add "$submodurl" submodule &&
+		test $(git ls-files --stage | grep ^160000 | wc -l) -eq 0
+	)
+'
+
 test_expect_success 'setup - add an example entry to .gitmodules' '
 	git config --file=.gitmodules submodule.example.url git://example.com/init.git
 '