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From: Jeff King <peff@peff.net>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
	Johannes Schindelin <Johannes.Schindelin@gmx.de>,
	Taylor Blau <me@ttaylorr.com>, Elijah Newren <newren@gmail.com>
Subject: Re: [PATCH 5/6] object-name.c: make dependency on object_type order more obvious
Date: Fri, 9 Apr 2021 14:36:02 -0400
Message-ID: <YHCekt1iXjy2NLrP@coredump.intra.peff.net> (raw)
In-Reply-To: <patch-5.6-94e13611f0-20210409T082935Z-avarab@gmail.com>

On Fri, Apr 09, 2021 at 10:32:53AM +0200, Ævar Arnfjörð Bjarmason wrote:

> Add an assert to make it more obvious that we were effectively
> hardcoding OBJ_TAG in sort_ambiguous() as "4".
> 
> I wrote this code in 5cc044e0257 (get_short_oid: sort ambiguous
> objects by type, then SHA-1, 2018-05-10), there was already a comment
> about this magic, but let's make sure that someone doing a potential
> reordering of "enum object_type" in the future would notice it
> breaking this function (and probably a bunch of other things...).

Yeah, those object type values are used for the on-disk formats, so
quite a lot would break.

> @@ -408,6 +408,8 @@ static int sort_ambiguous(const void *a, const void *b, void *ctx)
>  	enum object_type b_type = oid_object_info(sort_ambiguous_repo, b, NULL);
>  	enum object_type a_type_sort;
>  	enum object_type b_type_sort;
> +	const enum object_type tag_type_offs = OBJ_TAG - OBJ_NONE;
> +	assert(tag_type_offs == 4);

This protects us against shifting of the values or reordering within the
main 4 types, but it doesn't protect against new types, nor reordering
in which the main 4 types are no longer contiguous. E.g.:

  enum object_type {
          OBJ_NONE = 0,
	  OBJ_REF_DELTA = 1,
	  OBJ_OFS_DELTA = 2,
	  OBJ_COMMIT = 3,
	  OBJ_TAG = 4,
	  OBJ_BLOB = 5,
	  OBJ_TREE = 6,
  };

would be wrong. I dunno. I guess in some sense I am glad to see an
attempt at automated enforcement of assumptions. But I think if we are
worried about the object_type enum changing, we'd do better to write
this function in a less-clever way.

  /* sort tags before anything else */
  if (a_type == OBJ_TAG)
          a_type = 0;
  if (b_type == OBJ_TAG)
          b_type = 0;

Of course that is still assuming that normal values are all positive,
but that seems reasonable. If you really wanted to be agnostic, you
could assign the minimum value.  But you can't easily know that for an
enum. So you'd want to store them as ints (reversing your previous
commit!) and using INT_MIN.

The conditional probably performs less well in a tight loop, but I doubt
that matters for the size of array we expect to sort (if we cared about
performance we would not call oid_object_info() twice inside the
comparator!).

-Peff

  reply index

Thread overview: 142+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-06-22  0:33 [PATCH 0/2] Pull objects of various types Daniel Barkalow
2005-06-22  0:35 ` [PATCH 1/2] Parse tags for absent objects Daniel Barkalow
2021-03-08 20:04   ` [PATCH 0/7] improve reporting of unexpected objects Ævar Arnfjörð Bjarmason
2021-03-28  2:13     ` [PATCH v2 00/10] " Ævar Arnfjörð Bjarmason
2021-03-28  2:13       ` [PATCH v2 01/10] object.c: stop supporting len == -1 in type_from_string_gently() Ævar Arnfjörð Bjarmason
2021-03-28  5:35         ` Junio C Hamano
2021-03-28 15:46           ` Ævar Arnfjörð Bjarmason
2021-03-28 18:25             ` Junio C Hamano
2021-04-22 18:09               ` Felipe Contreras
2021-03-28  2:13       ` [PATCH v2 02/10] object.c: refactor type_from_string_gently() Ævar Arnfjörð Bjarmason
2021-03-28  2:13       ` [PATCH v2 03/10] object.c: make type_from_string() return "enum object_type" Ævar Arnfjörð Bjarmason
2021-03-28  2:13       ` [PATCH v2 04/10] object-file.c: make oid_object_info() " Ævar Arnfjörð Bjarmason
2021-03-28  2:13       ` [PATCH v2 05/10] object-name.c: make dependency on object_type order more obvious Ævar Arnfjörð Bjarmason
2021-03-28  2:13       ` [PATCH v2 06/10] tree.c: fix misindentation in parse_tree_gently() Ævar Arnfjörð Bjarmason
2021-03-28  2:13       ` [PATCH v2 07/10] object.c: add a utility function for "expected type X, got Y" Ævar Arnfjörð Bjarmason
2021-03-28  2:13       ` [PATCH v2 08/10] object.c: add and use oid_is_type_or_die_msg() function Ævar Arnfjörð Bjarmason
2021-03-28  2:13       ` [PATCH v2 09/10] object tests: add test for unexpected objects in tags Ævar Arnfjörð Bjarmason
2021-03-28  2:13       ` [PATCH v2 10/10] tag: don't misreport type of tagged objects in errors Ævar Arnfjörð Bjarmason
2021-03-30  5:50         ` Junio C Hamano
2021-03-31 11:02           ` Jeff King
2021-03-31 18:05             ` Junio C Hamano
2021-03-31 18:31             ` Ævar Arnfjörð Bjarmason
2021-03-31 18:59               ` Jeff King
2021-03-31 20:46                 ` Ævar Arnfjörð Bjarmason
2021-04-01  7:54                   ` Jeff King
2021-04-01  8:32                     ` [PATCH] ref-filter: fix NULL check for parse object failure Jeff King
2021-04-01 13:56                       ` [PATCH v2 0/5] mktag tests & fix for-each-ref segfault Ævar Arnfjörð Bjarmason
2021-04-01 13:56                         ` [PATCH v2 1/5] mktag tests: parse out options in helper Ævar Arnfjörð Bjarmason
2021-04-01 13:56                         ` [PATCH v2 2/5] mktag tests: invert --no-strict test Ævar Arnfjörð Bjarmason
2021-04-01 13:56                         ` [PATCH v2 3/5] mktag tests: do fsck on failure Ævar Arnfjörð Bjarmason
2021-04-01 13:56                         ` [PATCH v2 4/5] mktag tests: test for maybe segfaulting for-each-ref Ævar Arnfjörð Bjarmason
2021-04-01 13:56                         ` [PATCH v2 5/5] ref-filter: fix NULL check for parse object failure Ævar Arnfjörð Bjarmason
2021-04-01 19:19                           ` Ramsay Jones
2021-04-01 19:56                         ` [PATCH v2 0/5] mktag tests & fix for-each-ref segfault Junio C Hamano
2021-04-02 11:37                           ` Ævar Arnfjörð Bjarmason
2021-04-02 20:51                             ` Junio C Hamano
2021-04-01 19:52                       ` [PATCH] ref-filter: fix NULL check for parse object failure Junio C Hamano
2021-03-31 18:41             ` [PATCH v2 10/10] tag: don't misreport type of tagged objects in errors Junio C Hamano
2021-03-31 19:00               ` Jeff King
2021-03-28  9:27       ` [PATCH v2 00/10] improve reporting of unexpected objects Jeff King
2021-03-29 13:34         ` Ævar Arnfjörð Bjarmason
2021-03-31 10:43           ` Jeff King
2021-04-09  8:07       ` [PATCH 0/2] blob/object.c: trivial readability improvements Ævar Arnfjörð Bjarmason
2021-04-09  8:07         ` [PATCH 1/2] blob.c: remove buffer & size arguments to parse_blob_buffer() Ævar Arnfjörð Bjarmason
2021-04-09 17:51           ` Jeff King
2021-04-09 22:31             ` Junio C Hamano
2021-04-10 12:57             ` Ævar Arnfjörð Bjarmason
2021-04-10 13:01               ` Ævar Arnfjörð Bjarmason
2021-04-13  8:25               ` Jeff King
2021-04-09  8:07         ` [PATCH 2/2] object.c: initialize automatic variable in lookup_object() Ævar Arnfjörð Bjarmason
2021-04-09 17:53           ` Jeff King
2021-04-09 22:32             ` Junio C Hamano
2021-04-09  8:32         ` [PATCH 0/6] {tag,object}*.c: refactorings + prep for a larger change Ævar Arnfjörð Bjarmason
2021-04-09  8:32           ` [PATCH 1/6] object.c: stop supporting len == -1 in type_from_string_gently() Ævar Arnfjörð Bjarmason
2021-04-09 18:06             ` Jeff King
2021-04-09 18:10               ` Jeff King
2021-04-09  8:32           ` [PATCH 2/6] object.c: remove "gently" argument to type_from_string_gently() Ævar Arnfjörð Bjarmason
2021-04-09 18:10             ` Jeff King
2021-04-09  8:32           ` [PATCH 3/6] object.c: make type_from_string() return "enum object_type" Ævar Arnfjörð Bjarmason
2021-04-09 18:14             ` Jeff King
2021-04-09 19:42               ` Ævar Arnfjörð Bjarmason
2021-04-09 21:29                 ` Jeff King
2021-04-09  8:32           ` [PATCH 4/6] object-file.c: make oid_object_info() " Ævar Arnfjörð Bjarmason
2021-04-09 18:24             ` Jeff King
2021-04-09  8:32           ` [PATCH 5/6] object-name.c: make dependency on object_type order more obvious Ævar Arnfjörð Bjarmason
2021-04-09 18:36             ` Jeff King [this message]
2021-04-09  8:32           ` [PATCH 6/6] tag.c: use type_from_string_gently() when parsing tags Ævar Arnfjörð Bjarmason
2021-04-09 18:42             ` Jeff King
2021-04-09  8:49           ` [PATCH 0/7] object.c: add and use "is expected" utility function + object_as_type() use Ævar Arnfjörð Bjarmason
2021-04-09  8:49             ` [PATCH 1/7] tree.c: fix misindentation in parse_tree_gently() Ævar Arnfjörð Bjarmason
2021-04-09  8:49             ` [PATCH 2/7] object.c: add a utility function for "expected type X, got Y" Ævar Arnfjörð Bjarmason
2021-04-09  8:49             ` [PATCH 3/7] object.c: add and use oid_is_type_or_die_msg() function Ævar Arnfjörð Bjarmason
2021-04-09  8:49             ` [PATCH 4/7] commit-graph: use obj->type, not object_as_type() Ævar Arnfjörð Bjarmason
2021-04-09  8:50             ` [PATCH 5/7] commit.c: don't use deref_tag() -> object_as_type() Ævar Arnfjörð Bjarmason
2021-04-09  8:50             ` [PATCH 6/7] object.c: normalize brace style in object_as_type() Ævar Arnfjörð Bjarmason
2021-04-09  8:50             ` [PATCH 7/7] object.c: remove "quiet" parameter from object_as_type() Ævar Arnfjörð Bjarmason
2021-04-20 13:36             ` [PATCH v2 0/8] object.c: add and use "is expected" utility function + object_as_type() use Ævar Arnfjörð Bjarmason
2021-04-20 13:36               ` [PATCH v2 1/8] tree.c: fix misindentation in parse_tree_gently() Ævar Arnfjörð Bjarmason
2021-04-20 13:36               ` [PATCH v2 2/8] object.c: add a utility function for "expected type X, got Y" Ævar Arnfjörð Bjarmason
2021-04-21 22:02                 ` Jonathan Tan
2021-04-22  6:10                   ` Ævar Arnfjörð Bjarmason
2021-04-20 13:36               ` [PATCH v2 3/8] object.c: add and use oid_is_type_or_die_msg() function Ævar Arnfjörð Bjarmason
2021-04-21 22:07                 ` Jonathan Tan
2021-04-21 23:28                 ` Josh Steadmon
2021-04-28  4:12                   ` Junio C Hamano
2021-04-20 13:36               ` [PATCH v2 4/8] commit-graph: use obj->type, not object_as_type() Ævar Arnfjörð Bjarmason
2021-04-20 13:36               ` [PATCH v2 5/8] branch tests: assert lookup_commit_reference_gently() error Ævar Arnfjörð Bjarmason
2021-04-20 13:36               ` [PATCH v2 6/8] commit.c: don't use deref_tag() -> object_as_type() Ævar Arnfjörð Bjarmason
2021-04-21 22:26                 ` Jonathan Tan
2021-04-20 13:36               ` [PATCH v2 7/8] object.c: normalize brace style in object_as_type() Ævar Arnfjörð Bjarmason
2021-04-20 13:37               ` [PATCH v2 8/8] object.c: remove "quiet" parameter from object_as_type() Ævar Arnfjörð Bjarmason
2021-04-20 13:00           ` [PATCH v2 00/10] {tag,object}*.c: refactorings + prep for a larger change Ævar Arnfjörð Bjarmason
2021-04-20 13:00             ` [PATCH v2 01/10] object.c: stop supporting len == -1 in type_from_string_gently() Ævar Arnfjörð Bjarmason
2021-04-20 13:00             ` [PATCH v2 02/10] object.c: remove "gently" argument to type_from_string_gently() Ævar Arnfjörð Bjarmason
2021-04-20 13:00             ` [PATCH v2 03/10] object.c: make type_from_string() return "enum object_type" Ævar Arnfjörð Bjarmason
2021-04-20 13:00             ` [PATCH v2 04/10] object-file.c: make oid_object_info() " Ævar Arnfjörð Bjarmason
2021-04-20 13:00             ` [PATCH v2 05/10] object-name.c: make dependency on object_type order more obvious Ævar Arnfjörð Bjarmason
2021-04-20 13:00             ` [PATCH v2 06/10] tag.c: use type_from_string_gently() when parsing tags Ævar Arnfjörð Bjarmason
2021-04-20 13:00             ` [PATCH v2 07/10] hash-object: pass along type length to object.c Ævar Arnfjörð Bjarmason
2021-04-20 13:00             ` [PATCH v2 08/10] hash-object: refactor nested else/if/if into else if/else if Ævar Arnfjörð Bjarmason
2021-04-20 13:00             ` [PATCH v2 09/10] hash-object: show usage on invalid --type Ævar Arnfjörð Bjarmason
2021-04-20 13:00             ` [PATCH v2 10/10] object.c: move type_from_string() code to its last user Ævar Arnfjörð Bjarmason
2021-04-20 12:50         ` [PATCH v2 00/10] object.c et al: tests, small bug fixes etc Ævar Arnfjörð Bjarmason
2021-04-20 12:50           ` [PATCH v2 01/10] cat-file tests: test for bogus type name handling Ævar Arnfjörð Bjarmason
2021-04-29  4:15             ` Junio C Hamano
2021-04-20 12:50           ` [PATCH v2 02/10] hash-object tests: more detailed test for invalid type Ævar Arnfjörð Bjarmason
2021-04-20 12:50           ` [PATCH v2 03/10] mktree tests: add test for invalid object type Ævar Arnfjörð Bjarmason
2021-04-20 12:50           ` [PATCH v2 04/10] object-file.c: take type id, not string, in read_object_with_reference() Ævar Arnfjörð Bjarmason
2021-04-29  4:37             ` Junio C Hamano
2021-04-20 12:50           ` [PATCH v2 05/10] {commit,tree,blob,tag}.c: add a create_{commit,tree,blob,tag}() Ævar Arnfjörð Bjarmason
2021-04-29  4:45             ` Junio C Hamano
2021-04-29 12:01               ` Ævar Arnfjörð Bjarmason
2021-04-20 12:50           ` [PATCH v2 06/10] blob.c: remove parse_blob_buffer() Ævar Arnfjörð Bjarmason
2021-04-29  4:51             ` Junio C Hamano
2021-04-20 12:50           ` [PATCH v2 07/10] object.c: simplify return semantic of parse_object_buffer() Ævar Arnfjörð Bjarmason
2021-04-20 12:50           ` [PATCH v2 08/10] object.c: don't go past "len" under die() in type_from_string_gently() Ævar Arnfjörð Bjarmason
2021-04-29  4:55             ` Junio C Hamano
2021-04-20 12:50           ` [PATCH v2 09/10] mktree: stop setting *ntr++ to NIL Ævar Arnfjörð Bjarmason
2021-04-29  5:01             ` Junio C Hamano
2021-04-20 12:50           ` [PATCH v2 10/10] mktree: emit a more detailed error when the <type> is invalid Ævar Arnfjörð Bjarmason
2021-03-08 20:04   ` [PATCH 1/7] object.c: refactor type_from_string_gently() Ævar Arnfjörð Bjarmason
2021-03-08 20:52     ` Taylor Blau
2021-03-09 10:46     ` Jeff King
2021-03-08 20:04   ` [PATCH 2/7] object.c: make type_from_string() return "enum object_type" Ævar Arnfjörð Bjarmason
2021-03-08 20:56     ` Taylor Blau
2021-03-08 21:48     ` Junio C Hamano
2021-03-08 20:04   ` [PATCH 3/7] oid_object_info(): " Ævar Arnfjörð Bjarmason
2021-03-08 21:54     ` Junio C Hamano
2021-03-08 22:32       ` Junio C Hamano
2021-03-09 10:34     ` Jeff King
2021-03-08 20:04   ` [PATCH 4/7] tree.c: fix misindentation in parse_tree_gently() Ævar Arnfjörð Bjarmason
2021-03-08 20:04   ` [PATCH 5/7] object.c: add a utility function for "expected type X, got Y" Ævar Arnfjörð Bjarmason
2021-03-08 20:59     ` Taylor Blau
2021-03-08 22:15     ` Junio C Hamano
2021-03-08 20:04   ` [PATCH 6/7] object tests: add test for unexpected objects in tags Ævar Arnfjörð Bjarmason
2021-03-09 10:44     ` Jeff King
2021-03-28  1:35       ` Ævar Arnfjörð Bjarmason
2021-03-28  9:06         ` Jeff King
2021-03-28 15:39           ` Ævar Arnfjörð Bjarmason
2021-03-29  9:16             ` Jeff King
2021-03-08 20:04   ` [PATCH 7/7] tag: don't misreport type of tagged objects in errors Ævar Arnfjörð Bjarmason
2005-06-22  0:35 ` [PATCH 2/2] Pull misc objects Daniel Barkalow

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