[PATCH v6 00/22] fsck: lib-ify object-file.c & better fsck "invalid object" error reporting

This improves fsck error reporting, see the examples in the commit
messages of 19/22, 21/22 and 22/22. To get there I've lib-ified more
thigs in object-file.c and the general object APIs, i.e. now we'll
return error codes instead of calling die() in these cases.

This series has been in "needs review" state for a while. This re-roll
is mainly to bump it for the list's attention, but while I was at it I
addressed point from Jonathan Tan raised in a previous round: use an
enum instead of int for the unpack_loose_header() return value.

I think the v3 of this got a detailed review, and the v3->v4 delta
wasn't that big (although one commit in particular is a bit tricky):

    https://lore.kernel.org/git/cover-00.21-00000000000-20210624T191754Z-avarab@gmail.com/ (local)

I.e. it's just this part being substantially different from v3:

    https://lore.kernel.org/git/patch-12.21-3f52149bfde-20210624T191755Z-avarab@gmail.com/ (local)
    https://lore.kernel.org/git/patch-13.21-ba632be1520-20210624T191755Z-avarab@gmail.com/ (local)
    https://lore.kernel.org/git/patch-14.21-ea4f446f5b1-20210624T191755Z-avarab@gmail.com/ (local)

The v5 was then a trivial change of moving away from the
test_create_repo() test helper:
https://lore.kernel.org/git/cover-00.21-00000000000-20210710T133203Z-avarab@gmail.com/ (local)

Perhaps this whole thing just needs to be split up, e.g. the first 7
commits could be some "improve fsck tests" series, the middle part
some general small refactoring, and the real meaty work as of 14/22
its own third series...

But I've resisted that because I think while this is rather long the
first parts adding tests for missing behavior should assure reviewers
that the later changes are all properly tested.

I know the end-goal here isn't all that exciting in itself, but I've
really wanted to improve various things around fsck-ing, bad object
reporting etc., and that's been stalled on this first step for a
while.

Ævar Arnfjörð Bjarmason (22):
  fsck tests: refactor one test to use a sub-repo
  fsck tests: add test for fsck-ing an unknown type
  cat-file tests: test for missing object with -t and -s
  cat-file tests: test that --allow-unknown-type isn't on by default
  rev-list tests: test for behavior with invalid object types
  cat-file tests: add corrupt loose object test
  cat-file tests: test for current --allow-unknown-type behavior
  object-file.c: don't set "typep" when returning non-zero
  cache.h: move object functions to object-store.h
  object-file.c: make parse_loose_header_extended() public
  object-file.c: add missing braces to loose_object_info()
  object-file.c: simplify unpack_loose_short_header()
  object-file.c: split up ternary in parse_loose_header()
  object-file.c: stop dying in parse_loose_header()
  object-file.c: guard against future bugs in loose_object_info()
  object-file.c: return -1, not "status" from unpack_loose_header()
  object-file.c: return -2 on "header too long" in unpack_loose_header()
  object-file.c: use "enum" return type for unpack_loose_header()
  fsck: don't hard die on invalid object types
  object-store.h: move read_loose_object() below 'struct object_info'
  fsck: report invalid types recorded in objects
  fsck: report invalid object type-path combinations

 builtin/fast-export.c  |   2 +-
 builtin/fsck.c         |  28 ++++++-
 builtin/index-pack.c   |   2 +-
 builtin/mktag.c        |   3 +-
 cache.h                |  10 ---
 object-file.c          | 178 +++++++++++++++++++++--------------------
 object-store.h         |  75 ++++++++++++++---
 object.c               |   4 +-
 pack-check.c           |   3 +-
 streaming.c            |  29 ++++---
 t/t1006-cat-file.sh    | 169 ++++++++++++++++++++++++++++++++++++++
 t/t1450-fsck.sh        |  64 +++++++++++----
 t/t6115-rev-list-du.sh |  11 +++
 13 files changed, 432 insertions(+), 146 deletions(-)

Range-diff against v5:
 1:  a1259cdedcb =  1:  ebe89f65354 fsck tests: refactor one test to use a sub-repo
 2:  634f991d7c6 =  2:  9072eef3be3 fsck tests: add test for fsck-ing an unknown type
 3:  ce9dcc423e9 =  3:  d442a309178 cat-file tests: test for missing object with -t and -s
 4:  50a20741e86 =  4:  0358273022f cat-file tests: test that --allow-unknown-type isn't on by default
 5:  f8d0b630d0a =  5:  82db40ebf8a rev-list tests: test for behavior with invalid object types
 6:  43335e653b8 =  6:  d1ffd21acc5 cat-file tests: add corrupt loose object test
 7:  a00dfea3fb8 =  7:  22ab12c2282 cat-file tests: test for current --allow-unknown-type behavior
 9:  e9520953956 =  8:  38e4266772d object-file.c: don't set "typep" when returning non-zero
 8:  387d7f08e61 =  9:  5b9278e7bb4 cache.h: move object functions to object-store.h
10:  a8b408eefe6 = 10:  b15ad53414b object-file.c: make parse_loose_header_extended() public
11:  31eee4da0e1 = 11:  326eb74545d object-file.c: add missing braces to loose_object_info()
12:  dae5cfabd57 = 12:  4f829e9b727 object-file.c: simplify unpack_loose_short_header()
13:  0d8385d8d12 = 13:  90489d9e6ec object-file.c: split up ternary in parse_loose_header()
14:  d1522291aee = 14:  7c9819d37c5 object-file.c: stop dying in parse_loose_header()
15:  13d4141a21b = 15:  3fb660ff944 object-file.c: guard against future bugs in loose_object_info()
16:  912c9edf362 = 16:  9e7dbfb4aa3 object-file.c: return -1, not "status" from unpack_loose_header()
17:  7e101f97646 ! 17:  f28c4f0dfb4 object-file.c: return -2 on "header too long" in unpack_loose_header()
    @@ Commit message
         MAX_HEADER_LEN limit, or other negative values for "unable to unpack
         <OID> header".
     
    -    I tried setting up an enum just for these three return values, but I
    -    think the result was less readable. Let's consider doing that if we
    -    gain even more return values. For now let's do the next best thing and
    -    enumerate our known return values, and BUG() if we encounter one we
    -    don't know about.
    -
         Signed-off-by: Ævar Arnfjörð Bjarmason [off-list ref]
     
      ## object-file.c ##
 -:  ----------- > 18:  1b7173a5b5b object-file.c: use "enum" return type for unpack_loose_header()
18:  3c04065b0b0 = 19:  ad1614dbb8d fsck: don't hard die on invalid object types
19:  ad920362594 = 20:  3bf3cf2299d object-store.h: move read_loose_object() below 'struct object_info'
20:  02a148af5cf = 21:  974f650cddf fsck: report invalid types recorded in objects
21:  730e0a6f805 ! 22:  804673a17b0 fsck: report invalid object type-path combinations
    @@ object-store.h: int oid_object_info_extended(struct repository *r,
      		      void **contents,
      		      struct object_info *oi,
      		      unsigned int oi_flags);
    -@@ object-store.h: int unpack_loose_header(git_zstream *stream, unsigned char *map,
    +@@ object-store.h: enum unpack_loose_header_result unpack_loose_header(git_zstream *stream,
      int parse_loose_header(const char *hdr, struct object_info *oi);
      
      int check_object_signature(struct repository *r, const struct object_id *oid,
-- 
2.33.0.815.g21c7aaf6073