Re: [PATCH v6 19/22] fsck: don't hard die on invalid object types

To do this we need to pass down the "OBJECT_INFO_ALLOW_UNKNOWN_TYPE"
flag from read_loose_object() through to parse_loose_header(). Since
the read_loose_object() function is only used in builtin/fsck.c we can
simply change it. See f6371f92104 (sha1_file: add read_loose_object()
function, 2017-01-13) for the introduction of read_loose_object().

Why are we complaining about a "hash mismatch" for an object of a type
we don't know about? We shouldn't. This is the bare minimal change
needed to not make fsck hard die on a repository that's been corrupted
in this manner. In subsequent commits we'll teach fsck to recognize
this particular type of corruption and emit a better error message.

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---
 builtin/fsck.c  |  3 ++-
 object-file.c   | 11 ++++++++---
 object-store.h  |  3 ++-
 t/t1450-fsck.sh | 14 +++++++-------
 4 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/builtin/fsck.c b/builtin/fsck.c
index b42b6fe21f7..082dadd5629 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c

@@ -601,7 +601,8 @@ static int fsck_loose(const struct object_id *oid, const char *path, void *data)
 	void *contents;
 	int eaten;

-	if (read_loose_object(path, oid, &type, &size, &contents) < 0) {
+	if (read_loose_object(path, oid, &type, &size, &contents,
+			      OBJECT_INFO_ALLOW_UNKNOWN_TYPE) < 0) {
 		errors_found |= ERROR_OBJECT;
 		error(_("%s: object corrupt or missing: %s"),
 		      oid_to_hex(oid), path);

diff --git a/object-file.c b/object-file.c
index 9484c7ce2be..0e6937fad73 100644
--- a/object-file.c
+++ b/object-file.c

@@ -2562,7 +2562,8 @@ int read_loose_object(const char *path,
 		      const struct object_id *expected_oid,
 		      enum object_type *type,
 		      unsigned long *size,
-		      void **contents)
+		      void **contents,
+		      unsigned int oi_flags)
 {
 	int ret = -1;
 	void *map = NULL;

@@ -2570,6 +2571,7 @@ int read_loose_object(const char *path,
 	git_zstream stream;
 	char hdr[MAX_HEADER_LEN];
 	struct object_info oi = OBJECT_INFO_INIT;
+	int allow_unknown = oi_flags & OBJECT_INFO_ALLOW_UNKNOWN_TYPE;
 	oi.typep = type;
 	oi.sizep = size;

@@ -2592,8 +2594,11 @@ int read_loose_object(const char *path,
 		git_inflate_end(&stream);
 		goto out;
 	}
-	if (*type < 0)
-		die(_("invalid object type"));
+	if (!allow_unknown && *type < 0) {
+		error(_("header for %s declares an unknown type"), path);
+		git_inflate_end(&stream);
+		goto out;
+	}