From: Glen Choo <chooglen@google.com>
To: Victoria Dye <vdye@github.com>, git@vger.kernel.org
Cc: Victoria Dye via GitGitGadget <gitgitgadget@gmail.com>,
Jonathan Tan <jonathantanmy@google.com>,
derrickstolee@github.com, gitster@pobox.com
Subject: Re: [PATCH] setup: copy repository_format using helper
Date: Tue, 13 Jun 2023 11:25:51 -0700 [thread overview]
Message-ID: <kl6llegnfccw.fsf@chooglen-macbookpro.roam.corp.google.com> (raw)
In-Reply-To: <9fb6d7b1-00b6-93ee-efec-9dd0ab91a66d@github.com>
Victoria Dye <vdye@github.com> writes:
>> - All of them 'copy' .partial_clone. Most perform a shallow copy of the
>> pointer, then set the .partial_clone = NULL so that it doesn't get
>> cleared by clear_repository_format(). However,
>> check_repository_format() copies the string deeply because the
>> repository_format is sometimes read back (it is an "out" parameter).
>> To accomodate both shallow copying and deep copying, toggle this
>> behavior using the "modify_fmt_ok" parameter.
>
> Do you have a specific example of this happening? I see two uses of
> 'check_repository_format()' in the codebase:
>
> 1. in 'enter_repo()' ('path.c')
> 2. in 'init_db()' ('init-db.c')
>
> The first one calls 'check_repository_format()' with 'NULL', which causes
> the function to create a temporary 'struct repository_format' that is then
> discarded at the end of the function - no need to worry about the value
> being cleared there.
>
> The second one does call 'check_repository_format()' with a 'struct
> repository_format' instance, but the 'partial_clone' field field is not
> accessed again after that. The only subsequent usages of the 'repo_fmt'
> variable in 'init_db()' are:
>
> - in 'validate_hash_algorithm()', where only the 'version' and 'hash_algo'
> fields are accessed.
> - in 'create_default_files()', where only 'hash_algo' is accessed.
>
> So, shouldn't it be safe to shallow-copy-and-NULL? But as I noted earlier
> [1], if you do that it'll make the name 'check_repository_format()' a bit
> misleading (since it's actually modifying its arg in place). So, if you
> update to always shallow copy, 'check_repository_format()' should be renamed
> to reflect its side effects.
My understanding of check_repository_format() is that it serves double
duty of doing a) setup of the_repository and b) populating an "out"
parameter with the appropriate values. IMO a) is the side effect that
could warrant the rename, and b) is the expected, "read-only" use case.
From that perspective, doing a shallow copy here isn't really
introducing a weird side-effect (because the arg to an "out" parameter
should be zero-ed out to begin with), but it's returning a 'wrong'
value. You're right that it's safe because the NULL-ed value isn't read
back right now, but it's not any good if this function gains more
callers.
Your point about not having side effects in check_*() is a good one
though, and I'm starting to feel doubtful that we should be doing setup
there either....
>> If you're comfortable with it, I would prefer for you to squash this
>> into your patches so that we don't just end up changing the same few
>> lines. If not, I'll Reviewed-by your patches (if I don't find any other
>> concerns on a re-read) and send this as a 1-patch on top.
>
> Reading through the commit message & patch, I'm still not convinced this
> refactor is a good idea - to me, it doesn't leave the code in a clearly
> better state. If you feel strongly that it does, though, I'm happy to leave
> it to others to review/decide but I would prefer that you keep it a separate
> patch submission on top.
Okay. Given how weird check_repository_format() and
discover_git_directory() are, I think we haven't done enough
investigation to properly consolidate this logic, and doing that
introduces quite a lot of scope creep. It feels very unsatisfactory that
we are propagating a pattern that is suspicious in some places and
outright wrong in others instead of cleaning up as we go and leaving it
in a better state for future authors, but this series does leave some
_other_ parts in a better state (removing the global), and I think it's
still a net positive.
The helper function might not be a good idea yet, but I'm convinced that
removing the setup from discover_git_directory() is a good idea. I think
this series would be in a better state if we get rid of the wrong
pattern instead of extending it. Unfortunately, I forgot to include that
change in the patch I sent (ugh) but here's a patch that _just_ includes
the discover_git_directory() change that I hope you can squash into your
series (and you can use whatever bits of my commit message you see fit).
----- >8 --------- >8 --------- >8 --------- >8 --------- >8 ----
diff --git a/setup.c b/setup.c
index 33ce58676f..b172ffd48a 100644
--- a/setup.c
+++ b/setup.c
@@ -1422,14 +1422,6 @@ int discover_git_directory(struct strbuf *commondir,
return -1;
}
- the_repository->repository_format_worktree_config =
- candidate.worktree_config;
-
- /* take ownership of candidate.partial_clone */
- the_repository->repository_format_partial_clone =
- candidate.partial_clone;
- candidate.partial_clone = NULL;
-
clear_repository_format(&candidate);
return 0;
}
----- >8 --------- >8 --------- >8 --------- >8 --------- >8 ----
You can see that this patch based on top of yours passes CI
https://github.com/git/git/commit/9469fe3a6b0efbe89d26ef096a2eebabea59c55f
https://github.com/chooglen/git/actions/runs/5258672473
> I think you may be missing changes to 'discover_git_directory()'? Like I
> mentioned above, though, if you don't think 'discover_git_directory()' needs
> to set up 'the_repository', then those assignments should just be removed
> (not replaced with 'setup_repository_from_format()').
Ah sorry, yes they were meant to be removed. I somehow missed those as I
was preparing the patch.
next prev parent reply other threads:[~2023-06-13 18:25 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-23 23:17 [PATCH 0/2] Fix behavior of worktree config in submodules Victoria Dye via GitGitGadget
2023-05-23 23:17 ` [PATCH 1/2] config: use gitdir to get worktree config Victoria Dye via GitGitGadget
2023-05-25 1:05 ` Glen Choo
2023-05-25 20:05 ` Derrick Stolee
2023-05-23 23:17 ` [PATCH 2/2] repository: move 'repository_format_worktree_config' to repo scope Victoria Dye via GitGitGadget
2023-05-25 1:29 ` Glen Choo
2023-05-25 16:09 ` Glen Choo
2023-05-25 20:02 ` Victoria Dye
2023-05-25 20:13 ` Derrick Stolee
2023-05-24 10:25 ` [PATCH 0/2] Fix behavior of worktree config in submodules Junio C Hamano
2023-05-25 19:56 ` Glen Choo
2023-05-26 1:32 ` [PATCH v2 0/3] " Victoria Dye via GitGitGadget
2023-05-26 1:32 ` [PATCH v2 1/3] config: use gitdir to get worktree config Victoria Dye via GitGitGadget
2023-05-26 1:32 ` [PATCH v2 2/3] config: pass 'repo' directly to 'config_with_options()' Victoria Dye via GitGitGadget
2023-05-26 1:33 ` [PATCH v2 3/3] repository: move 'repository_format_worktree_config' to repo scope Victoria Dye via GitGitGadget
2023-05-31 22:17 ` Glen Choo
2023-06-01 4:43 ` Junio C Hamano
2023-06-12 21:37 ` Glen Choo
2023-06-07 22:29 ` Victoria Dye
2023-06-12 18:10 ` Glen Choo
2023-06-12 19:45 ` Victoria Dye
2023-06-12 20:23 ` Glen Choo
2023-06-12 23:04 ` [PATCH] setup: copy repository_format using helper Glen Choo
2023-06-13 0:03 ` Victoria Dye
2023-06-13 18:25 ` Glen Choo [this message]
2023-06-13 19:45 ` Junio C Hamano
2023-05-26 15:48 ` [PATCH v2 0/3] Fix behavior of worktree config in submodules Derrick Stolee
2023-06-13 22:09 ` Glen Choo
2023-06-13 22:17 ` Victoria Dye
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