From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Derrick Stolee <derrickstolee@github.com>
Cc: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>,
git@vger.kernel.org
Subject: Re: [PATCH 4/5] config: return an empty list, not NULL
Date: Tue, 27 Sep 2022 21:18:48 +0200 [thread overview]
Message-ID: <220927.86k05oy5oi.gmgdl@evledraar.gmail.com> (raw)
In-Reply-To: <b85d8a43-6640-aa9c-3103-0c3d43c2a479@github.com>
On Tue, Sep 27 2022, Derrick Stolee wrote:
> On 9/27/2022 12:21 PM, Ævar Arnfjörð Bjarmason wrote:
>>
>> On Tue, Sep 27 2022, Derrick Stolee via GitGitGadget wrote:
>
>>> /**
>>> * Finds and returns the value list, sorted in order of increasing priority
>>> * for the configuration variable `key`. When the configuration variable
>>> - * `key` is not found, returns NULL. The caller should not free or modify
>>> - * the returned pointer, as it is owned by the cache.
>>> + * `key` is not found, returns an empty list. The caller should not free or
>>> + * modify the returned pointer, as it is owned by the cache.
>>> */
>>> const struct string_list *git_config_get_value_multi(const char *key);
>>
>> Aside from the "DWIM API" aspect of this (which I don't mind) I think
>> this is really taking the low-level function in the wrong direction, and
>> that we should just add a new simple wrapper instead.
>>
>> I.e. both the pre-image API docs & this series gloss over the fact that
>> we'd not just return NULL here if the config wasn't there, but also if
>> git_config_parse_key() failed.
>>
>> So it seems to me that a better direction would be starting with
>> something like the WIP below (which doesn't compile the whole code, I
>> stopped at config.[ch] and pack-bitmap.c). I.e. the same "int" return
>> and "dest" pattern that most other things in the config API have.
>
> Do you have an example where a caller would benefit from this
> distinction? Without such an example, I don't think it is worth
> creating such a huge change for purity's sake alone.
Not initially, I started poking at this because the CL/series/commits
says that we don't care about the case of non-existing keys, without
being clear as to why we want to conflate that with other errors we
might get from this API.
But after some digging I found:
$ for k in a a.b. "'x.y"; do ./git for-each-repo --config=$k; echo $?; done
error: key does not contain a section: a
0
error: key does not contain variable name: a.b.
0
error: invalid key: 'x.y
0
I.e. the repo_config_get_value_multi() you added in for-each-repo
doesn't distinguish between bad keys and non-existing keys, and returns
0 even though it printed an "error".
> I'm pretty happy that the diff for this series is an overall
> reduction in code, while also not being too large in the interim:
>
> 12 files changed, 39 insertions(+), 57 deletions(-)
>
> If all callers that use the *_multi() methods would only use the
> wrapper, then what is the point of doing the low-level manipulations?
I hacked up something that's at least RFC-quality based on this
approach, but CI is running etc., so not submitting it
now:
https://github.com/git/git/compare/master...avar:git:avar/have-git_configset_get_value-use-dest-and-int-pattern
I think the resulting diff is more idiomatic API use, i.e. you ended up
with:
/* submodule.active is set */
sl = repo_config_get_value_multi(repo, "submodule.active");
- if (sl) {
+ if (sl && sl->nr) {
But I ended up doing:
/* submodule.active is set */
- sl = repo_config_get_value_multi(repo, "submodule.active");
- if (sl) {
+ if (!repo_config_get_const_value_multi(repo, "submodule.active", &sl)) {
Note the "const" in the function name, i.e. there's wrappers that handle
the case where we have a hardcoded key name, in which case we can BUG()
out if we'd return < 0, so all we have left is just "does key exist".
In any case, I'm all for having some simple wrapper for the common cases.
But I didn't find a single case where we actually needed this "never
give me a non-NULL list" behavior, it could just be generalized to
"let's have the API tell us if the key exist".
If you use the non-"const" API you can distinguish the err < 0 case, so
for-each-repo can now error out appropriately:
$ ./git for-each-repo --config=a; echo $?
error: key does not contain a section: a
fatal: got bad config --config=a
usage: git for-each-repo --config=<config> <command-args>
--config <config> config key storing a list of repository paths
129
next prev parent reply other threads:[~2022-09-27 19:32 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-27 14:08 [PATCH 0/5] [RFC] config API: return empty list, not NULL Derrick Stolee via GitGitGadget
2022-09-27 14:08 ` [PATCH 1/5] config: relax requirements on multi-value return Derrick Stolee via GitGitGadget
2022-09-27 17:26 ` Junio C Hamano
2022-09-27 14:08 ` [PATCH 2/5] *: relax git_configset_get_value_multi result Derrick Stolee via GitGitGadget
2022-09-28 15:58 ` Taylor Blau
2022-09-27 14:08 ` [PATCH 3/5] config: add BUG() statement instead of possible segfault Derrick Stolee via GitGitGadget
2022-09-27 16:17 ` Ævar Arnfjörð Bjarmason
2022-09-27 16:46 ` Derrick Stolee
2022-09-27 17:22 ` Ævar Arnfjörð Bjarmason
2022-09-27 14:08 ` [PATCH 4/5] config: return an empty list, not NULL Derrick Stolee via GitGitGadget
2022-09-27 16:21 ` Ævar Arnfjörð Bjarmason
2022-09-27 16:50 ` Derrick Stolee
2022-09-27 19:18 ` Ævar Arnfjörð Bjarmason [this message]
2022-09-28 13:46 ` Derrick Stolee
2022-09-28 14:37 ` Ævar Arnfjörð Bjarmason
2022-09-28 18:10 ` Derrick Stolee
2022-09-28 19:33 ` Ævar Arnfjörð Bjarmason
2022-09-27 14:08 ` [PATCH 5/5] *: expect a non-NULL list of config values Derrick Stolee via GitGitGadget
2022-09-28 2:40 ` [PATCH 0/5] [RFC] config API: return empty list, not NULL Junio C Hamano
2022-09-28 18:38 ` Derrick Stolee
2022-09-28 19:27 ` Ævar Arnfjörð Bjarmason
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