From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Jeff King <peff@peff.net>
Cc: Junio C Hamano <gitster@pobox.com>,
git@vger.kernel.org,
"brian m . carlson" <sandals@crustytoothpaste.net>,
Derrick Stolee <stolee@gmail.com>,
Stefan Beller <sbeller@google.com>,
Eric Sunshine <sunshine@sunshineco.com>
Subject: Re: [PATCH v3 09/12] get_short_oid / peel_onion: ^{tree} should be tree, not treeish
Date: Tue, 08 May 2018 20:53:10 +0200 [thread overview]
Message-ID: <87a7tax9m1.fsf@evledraar.gmail.com> (raw)
In-Reply-To: <20180508143408.GA30183@sigill.intra.peff.net>
On Tue, May 08 2018, Jeff King wrote:
> On Mon, May 07, 2018 at 01:08:46PM +0900, Junio C Hamano wrote:
>
>> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>>
>> > Right, and I'm with you so far, this makes sense to me for all existing
>> > uses of the peel syntax, otherwise v2.17.0^{tree} wouldn't be the same
>> > as rev-parse v2.17.0^{tree}^{tree}...
>>
>> More importantly, you could spell v2.17.0 part of the above with a
>> short hexadecimal string. And that string should be naming some
>> tree-ish, the most important thing being that it is *NOT* required
>> to be a tree (and practically, it is likely that the user has a
>> tree-ish that is *NOT* a tree).
>>
>> I guess I have a reaction to the title
>>
>> "get_short_oid/peel_onion: ^{tree} should be tree"
>>
>> "X^{tree}" should *RESULT* in a tree, but it should *REQUIRE* X to
>> be a tree-ish. It is unclear "should be tree" is about the former
>> and I read (perhaps mis-read) it as saying "it should require X to
>> be a tree"---that statement is utterly incorrect as we agreed above.
>
> FWIW, I had the same feeling as you when reading this, that this commit
> (and the one after) are doing the wrong thing. And these paragraphs sum
> it up. The "^{tree}" is about asking us to peel to a tree, not about
> resolving X in the first place. We can use it as a _hint_ when resolving
> X, but the correct hint is "something that can be peeled to a tree", not
> "is definitely a tree".
Maybe I'm just being dense, but I still don't get from this & Junio's
E-Mails what the general rule should be.
I think a response to the part after "leaving that aside" of my upthread
E-Mail
(https://public-inbox.org/git/87lgczyfq6.fsf@evledraar.gmail.com/) would
help me out.
Not to belabor the point, but here's a patch I came up with to
revisions.txt that's a WIP version of something that would describe the
worldview after this v3:
diff --git a/Documentation/revisions.txt b/Documentation/revisions.txt
index dfcc49c72c..0bf68f4ad2 100644
--- a/Documentation/revisions.txt
+++ b/Documentation/revisions.txt
@@ -143,29 +143,52 @@ thing no matter the case.
'<rev>{caret}1{caret}1{caret}1'. See below for an illustration of
the usage of this form.
'<rev>{caret}{<type>}', e.g. 'v0.99.8{caret}\{commit\}'::
A suffix '{caret}' followed by an object type name enclosed in
brace pair means dereference the object at '<rev>' recursively until
an object of type '<type>' is found or the object cannot be
- dereferenced anymore (in which case, barf).
+ dereferenced anymore (in which case either return that object type, or barf).
For example, if '<rev>' is a commit-ish, '<rev>{caret}\{commit\}'
describes the corresponding commit object.
Similarly, if '<rev>' is a tree-ish, '<rev>{caret}\{tree\}'
describes the corresponding tree object.
'<rev>{caret}0'
is a short-hand for '<rev>{caret}\{commit\}'.
+
'rev{caret}\{object\}' can be used to make sure 'rev' names an
object that exists, without requiring 'rev' to be a tag, and
without dereferencing 'rev'; because a tag is already an object,
it does not have to be dereferenced even once to get to an object.
+
'rev{caret}\{tag\}' can be used to ensure that 'rev' identifies an
existing tag object.
++
+Object types that don't have a 1=1 mapping to other object types
+cannot be dereferenced with the peel syntax, and will return an
+error. E.g. '<treeid>{caret}{commit}' or '<treeid>{caret}{tree}' is
+allowed because a tag can only point to one commit, and a commit can
+only point to one tree. But '<treeid>{caret}{blob}' will always
+produce an error since trees in general don't 1=1 map to blobs, even
+though the specific '<treeid>' in question might only contain one
+blob. Note that '<tagid>{caret}{blob}' is not an error if '<tagid>' is
+a tag that points directly to a blob, since that again becomes
+unambiguous.
++
+'<rev>{caret}{<type>}' takes on a different meaning when '<rev>' is a
+SHA-1 that's ambiguous within the object store. In that case we don't
+have a 1=1 mapping anymore. E.g. e8f2 in git.git can refer to multiple
+objects of all the different object types. In that case
+{caret}{<type>} should always be an error to be consistent with the
+logic above, but that wouldn't be useful to anybody. Instead it'll
+fall back to being selector syntax for the given object types,
+e.g. e8f2{caret}{tag} will (as of writing this) return the v2.17.0
+tag, and {caret}{commit}, {caret}{tree} and {caret}{blob} will return
+commit, tree and blob objects, respectively.
+
[...]
My understanding of what you two are saying is that somehow the peel
semantics should be preserved when we take this beyond the 1=1 mapping
case, but I don't see how if we run with that how we wouldn't need to
introduce the concept of blobish for consistency as I noted upthread.
So it would be very useful to me if you or someone who understands the
behavior you & Junio seem to want could write a version of the patch I
have above where the last paragraph is different, and describes the
desired semantics, because I still don't get it. Why would we 1=many
peel commits to trees as a special case, but not 1=many do the same for
trees & blobs?
next prev parent reply other threads:[~2018-05-08 18:53 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-30 22:07 [PATCH 0/9] get_short_oid UI improvements Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 1/9] sha1-name.c: remove stray newline Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 2/9] sha1-array.h: align function arguments Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 3/9] sha1-name.c: move around the collect_ambiguous() function Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 4/9] get_short_oid: sort ambiguous objects by type, then SHA-1 Ævar Arnfjörð Bjarmason
2018-05-01 11:11 ` Derrick Stolee
2018-05-01 11:27 ` Ævar Arnfjörð Bjarmason
2018-05-01 12:26 ` Derrick Stolee
2018-05-01 12:36 ` Ævar Arnfjörð Bjarmason
2018-05-01 13:05 ` Derrick Stolee
2018-04-30 22:07 ` [PATCH 5/9] get_short_oid: learn to disambiguate by ^{tag} Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 6/9] get_short_oid: learn to disambiguate by ^{blob} Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 7/9] get_short_oid / peel_onion: ^{tree} should mean tree, not treeish Ævar Arnfjörð Bjarmason
2018-05-01 1:13 ` brian m. carlson
2018-04-30 22:07 ` [PATCH 8/9] get_short_oid / peel_onion: ^{tree} should mean commit, not commitish Ævar Arnfjörð Bjarmason
2018-04-30 23:22 ` Eric Sunshine
2018-04-30 22:07 ` [PATCH 9/9] config doc: document core.disambiguate Ævar Arnfjörð Bjarmason
2018-04-30 22:34 ` [PATCH 0/9] get_short_oid UI improvements Stefan Beller
2018-05-01 1:27 ` brian m. carlson
2018-05-01 11:16 ` Derrick Stolee
2018-05-01 12:06 ` [PATCH v2 00/12] " Ævar Arnfjörð Bjarmason
2018-05-01 13:03 ` [PATCH v2 06/11] get_short_oid: sort ambiguous objects by type, then SHA-1 Derrick Stolee
2018-05-01 13:39 ` Ævar Arnfjörð Bjarmason
2018-05-01 13:44 ` Derrick Stolee
2018-05-01 14:10 ` Ævar Arnfjörð Bjarmason
2018-05-01 14:15 ` Derrick Stolee
2018-05-01 18:40 ` [PATCH v3 00/12] get_short_oid UI improvements Ævar Arnfjörð Bjarmason
2018-05-02 12:42 ` Derrick Stolee
2018-05-02 13:45 ` Derrick Stolee
2018-05-03 6:43 ` Jacob Keller
2018-05-01 18:40 ` [PATCH v3 01/12] sha1-name.c: remove stray newline Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 02/12] sha1-array.h: align function arguments Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 03/12] git-p4: change "commitish" typo to "committish" Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 04/12] cache.h: add comment explaining the order in object_type Ævar Arnfjörð Bjarmason
2018-05-03 5:05 ` Junio C Hamano
2018-05-08 15:35 ` Duy Nguyen
2018-05-08 15:56 ` [PATCH] pack-format.txt: more details on pack file format Nguyễn Thái Ngọc Duy
2018-05-08 17:23 ` Stefan Beller
2018-05-08 18:22 ` Duy Nguyen
2018-05-08 18:58 ` Stefan Beller
2018-05-08 18:21 ` Ævar Arnfjörð Bjarmason
2018-05-08 18:24 ` Duy Nguyen
2018-05-10 15:09 ` [PATCH v2] " Nguyễn Thái Ngọc Duy
2018-05-10 17:06 ` Stefan Beller
2018-05-11 6:41 ` Duy Nguyen
2018-05-11 3:54 ` Junio C Hamano
2018-05-11 6:55 ` [PATCH v3] " Nguyễn Thái Ngọc Duy
2018-05-01 18:40 ` [PATCH v3 05/12] sha1-name.c: move around the collect_ambiguous() function Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 06/12] get_short_oid: sort ambiguous objects by type, then SHA-1 Ævar Arnfjörð Bjarmason
2018-05-03 5:13 ` Junio C Hamano
2018-05-08 14:44 ` Jeff King
2018-05-01 18:40 ` [PATCH v3 07/12] get_short_oid: learn to disambiguate by ^{tag} Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 08/12] get_short_oid: learn to disambiguate by ^{blob} Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 09/12] get_short_oid / peel_onion: ^{tree} should be tree, not treeish Ævar Arnfjörð Bjarmason
2018-05-03 5:28 ` Junio C Hamano
2018-05-03 7:28 ` Ævar Arnfjörð Bjarmason
2018-05-04 2:19 ` Junio C Hamano
2018-05-04 8:42 ` Ævar Arnfjörð Bjarmason
2018-05-07 4:08 ` Junio C Hamano
2018-05-08 14:34 ` Jeff King
2018-05-08 18:53 ` Ævar Arnfjörð Bjarmason [this message]
2018-05-09 7:56 ` Jeff King
2018-05-09 10:48 ` Ævar Arnfjörð Bjarmason
2018-05-10 4:21 ` Junio C Hamano
2018-05-10 6:50 ` Jeff King
2018-05-10 12:42 ` [PATCH v4 0/6] get_short_oid UI improvements Ævar Arnfjörð Bjarmason
2018-05-10 16:04 ` Jeff King
2018-05-10 12:42 ` [PATCH v4 1/6] sha1-name.c: remove stray newline Ævar Arnfjörð Bjarmason
2018-05-10 12:42 ` [PATCH v4 2/6] sha1-array.h: align function arguments Ævar Arnfjörð Bjarmason
2018-05-10 15:06 ` Jeff King
2018-05-11 3:07 ` Junio C Hamano
2018-05-11 3:09 ` Junio C Hamano
2018-05-10 12:43 ` [PATCH v4 3/6] git-p4: change "commitish" typo to "committish" Ævar Arnfjörð Bjarmason
2018-05-10 15:00 ` Luke Diamand
2018-05-10 12:43 ` [PATCH v4 4/6] sha1-name.c: move around the collect_ambiguous() function Ævar Arnfjörð Bjarmason
2018-05-10 12:43 ` [PATCH v4 5/6] get_short_oid: sort ambiguous objects by type, then SHA-1 Ævar Arnfjörð Bjarmason
2018-05-10 15:22 ` Jeff King
2018-05-11 5:36 ` Junio C Hamano
2018-05-10 12:43 ` [PATCH v4 6/6] get_short_oid: document & warn if we ignore the type selector Ævar Arnfjörð Bjarmason
2018-05-10 13:15 ` Martin Ågren
2018-05-10 16:03 ` Jeff King
2018-05-10 16:10 ` Jeff King
2018-05-10 16:15 ` Jeff King
2018-05-01 18:40 ` [PATCH v3 10/12] get_short_oid / peel_onion: ^{commit} should be commit, not committish Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 11/12] config doc: document core.disambiguate Ævar Arnfjörð Bjarmason
2018-05-08 14:41 ` Jeff King
2018-05-01 18:40 ` [PATCH v3 12/12] get_short_oid: document & warn if we ignore the type selector Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 01/12] sha1-name.c: remove stray newline Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 02/12] sha1-array.h: align function arguments Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 03/12] git-p4: change "commitish" typo to "committish" Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 04/12] cache.h: add comment explaining the order in object_type Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 05/12] sha1-name.c: move around the collect_ambiguous() function Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 06/12] get_short_oid: sort ambiguous objects by type, then SHA-1 Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 07/12] get_short_oid: learn to disambiguate by ^{tag} Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 08/12] get_short_oid: learn to disambiguate by ^{blob} Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 09/12] get_short_oid / peel_onion: ^{tree} should be tree, not treeish Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 10/12] get_short_oid / peel_onion: ^{commit} should be commit, not committish Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 11/12] config doc: document core.disambiguate Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 12/12] get_short_oid: document & warn if we ignore the type selector Ævar Arnfjörð Bjarmason
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