Merge branch 'bc/sha1-256-interop-01'

The beginning of SHA1-SHA256 interoperability work.

* bc/sha1-256-interop-01:
  t1010: use BROKEN_OBJECTS prerequisite
  t: allow specifying compatibility hash
  fsck: consider gpgsig headers expected in tags
  rev-parse: allow printing compatibility hash
  docs: add documentation for loose objects
  docs: improve ambiguous areas of pack format documentation
  docs: reflect actual double signature for tags
  docs: update offset order for pack index v3
  docs: update pack index v3 format

5 files changed, 116 insertions, 7 deletions

diff --git a/t/t1010-mktree.sh b/t/t1010-mktree.sh
index e9973f7494..312fe6717a 100755
--- a/t/t1010-mktree.sh
+++ b/t/t1010-mktree.sh
@@ -11,10 +11,13 @@ test_expect_success setup '
 		git add "$d" || return 1
 	done &&
 	echo zero >one &&
-	git update-index --add --info-only one &&
-	git write-tree --missing-ok >tree.missing &&
-	git ls-tree $(cat tree.missing) >top.missing &&
-	git ls-tree -r $(cat tree.missing) >all.missing &&
+	if test_have_prereq BROKEN_OBJECTS
+	then
+		git update-index --add --info-only one &&
+		git write-tree --missing-ok >tree.missing &&
+		git ls-tree $(cat tree.missing) >top.missing &&
+		git ls-tree -r $(cat tree.missing) >all.missing
+	fi &&
 	echo one >one &&
 	git add one &&
 	git write-tree >tree &&
@@ -53,7 +56,7 @@ test_expect_success 'ls-tree output in wrong order given to mktree (2)' '
 	test_cmp tree.withsub actual
 '
 
-test_expect_success 'allow missing object with --missing' '
+test_expect_success BROKEN_OBJECTS 'allow missing object with --missing' '
 	git mktree --missing <top.missing >actual &&
 	test_cmp tree.missing actual
 '
diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index 5ae86c42be..c4b651c2dc 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -454,6 +454,60 @@ test_expect_success 'tag with NUL in header' '
 	test_grep "error in tag $tag.*unterminated header: NUL at offset" out
 '
 
+test_expect_success 'tag accepts gpgsig header even if not validly signed' '
+	test_oid_cache <<-\EOF &&
+	header sha1:gpgsig-sha256
+	header sha256:gpgsig
+	EOF
+	header=$(test_oid header) &&
+	sha=$(git rev-parse HEAD) &&
+	cat >good-tag <<-EOF &&
+	object $sha
+	type commit
+	tag good
+	tagger T A Gger <tagger@example.com> 1234567890 -0000
+	$header -----BEGIN PGP SIGNATURE-----
+	 Not a valid signature
+	 -----END PGP SIGNATURE-----
+
+	This is a good tag.
+	EOF
+
+	tag=$(git hash-object --literally -t tag -w --stdin <good-tag) &&
+	test_when_finished "remove_object $tag" &&
+	git update-ref refs/tags/good $tag &&
+	test_when_finished "git update-ref -d refs/tags/good" &&
+	git -c fsck.extraHeaderEntry=error fsck --tags
+'
+
+test_expect_success 'tag rejects invalid headers' '
+	test_oid_cache <<-\EOF &&
+	header sha1:gpgsig-sha256
+	header sha256:gpgsig
+	EOF
+	header=$(test_oid header) &&
+	sha=$(git rev-parse HEAD) &&
+	cat >bad-tag <<-EOF &&
+	object $sha
+	type commit
+	tag good
+	tagger T A Gger <tagger@example.com> 1234567890 -0000
+	$header -----BEGIN PGP SIGNATURE-----
+	 Not a valid signature
+	 -----END PGP SIGNATURE-----
+	junk
+
+	This is a bad tag with junk at the end of the headers.
+	EOF
+
+	tag=$(git hash-object --literally -t tag -w --stdin <bad-tag) &&
+	test_when_finished "remove_object $tag" &&
+	git update-ref refs/tags/bad $tag &&
+	test_when_finished "git update-ref -d refs/tags/bad" &&
+	test_must_fail git -c fsck.extraHeaderEntry=error fsck --tags 2>out &&
+	test_grep "error in tag $tag.*invalid format - extra header" out
+'
+
 test_expect_success 'cleaned up' '
 	git fsck >actual 2>&1 &&
 	test_must_be_empty actual
diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
index 58a4583088..7739ab611b 100755
--- a/t/t1500-rev-parse.sh
+++ b/t/t1500-rev-parse.sh
@@ -207,6 +207,40 @@ test_expect_success 'rev-parse --show-object-format in repo' '
 	grep "unknown mode for --show-object-format: squeamish-ossifrage" err
 '
 
+
+test_expect_success 'rev-parse --show-object-format in repo with compat mode' '
+	mkdir repo &&
+	(
+		sane_unset GIT_DEFAULT_HASH &&
+		cd repo &&
+		git init --object-format=sha256 &&
+		git config extensions.compatobjectformat sha1 &&
+		echo sha256 >expect &&
+		git rev-parse --show-object-format >actual &&
+		test_cmp expect actual &&
+		git rev-parse --show-object-format=storage >actual &&
+		test_cmp expect actual &&
+		git rev-parse --show-object-format=input >actual &&
+		test_cmp expect actual &&
+		git rev-parse --show-object-format=output >actual &&
+		test_cmp expect actual &&
+		echo sha1 >expect &&
+		git rev-parse --show-object-format=compat >actual &&
+		test_cmp expect actual &&
+		test_must_fail git rev-parse --show-object-format=squeamish-ossifrage 2>err &&
+		grep "unknown mode for --show-object-format: squeamish-ossifrage" err
+	) &&
+	mkdir repo2 &&
+	(
+		sane_unset GIT_DEFAULT_HASH &&
+		cd repo2 &&
+		git init --object-format=sha256 &&
+		echo >expect &&
+		git rev-parse --show-object-format=compat >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'rev-parse --show-ref-format' '
 	test_detect_ref_format >expect &&
 	git rev-parse --show-ref-format >actual &&
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index a28de7b19b..52d7759bf5 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1708,11 +1708,16 @@ test_set_hash () {
 # Detect the hash algorithm in use.
 test_detect_hash () {
 	case "${GIT_TEST_DEFAULT_HASH:-$GIT_TEST_BUILTIN_HASH}" in
-	"sha256")
+	*:*)
+	    test_hash_algo="${GIT_TEST_DEFAULT_HASH%%:*}"
+	    test_compat_hash_algo="${GIT_TEST_DEFAULT_HASH##*:}"
+	    test_repo_compat_hash_algo="$test_compat_hash_algo"
+	    ;;
+	sha256)
 	    test_hash_algo=sha256
 	    test_compat_hash_algo=sha1
 	    ;;
-	*)
+	sha1)
 	    test_hash_algo=sha1
 	    test_compat_hash_algo=sha256
 	    ;;
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 562f950fb0..ef0ab7ec2d 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1924,6 +1924,19 @@ test_lazy_prereq DEFAULT_HASH_ALGORITHM '
 test_lazy_prereq DEFAULT_REPO_FORMAT '
 	test_have_prereq SHA1,REFFILES
 '
+# BROKEN_OBJECTS is a test whether we can write deliberately broken objects and
+# expect them to work.  When running using SHA-256 mode with SHA-1
+# compatibility, we cannot write such objects because there's no SHA-1
+# compatibility value for a nonexistent object.
+test_lazy_prereq BROKEN_OBJECTS '
+	! test_have_prereq COMPAT_HASH
+'
+
+# COMPAT_HASH is a test if we're operating in a repository with SHA-256 with
+# SHA-1 compatibility.
+test_lazy_prereq COMPAT_HASH '
+	test -n "$test_repo_compat_hash_algo"
+'
 
 # Ensure that no test accidentally triggers a Git command
 # that runs the actual maintenance scheduler, affecting a user's